/* * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.lang.invoke; import java.lang.reflect.*; import sun.invoke.util.ValueConversions; import sun.invoke.util.VerifyAccess; import sun.invoke.util.Wrapper; import java.util.List; import java.util.ArrayList; import java.util.Arrays; import sun.reflect.CallerSensitive; import sun.reflect.Reflection; import sun.reflect.misc.ReflectUtil; import static java.lang.invoke.MethodHandleStatics.*; import static java.lang.invoke.MethodHandleNatives.Constants.*; import sun.security.util.SecurityConstants; /** * This class consists exclusively of static methods that operate on or return * method handles. They fall into several categories: * *

* @author John Rose, JSR 292 EG */ public class MethodHandles { private MethodHandles() { } // do not instantiate private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory(); static { MethodHandleImpl.initStatics(); } // See IMPL_LOOKUP below. //// Method handle creation from ordinary methods. /** * Returns a {@link Lookup lookup object} on the caller, * which has the capability to access any method handle that the caller has access to, * including direct method handles to private fields and methods. * This lookup object is a capability which may be delegated to trusted agents. * Do not store it in place where untrusted code can access it. */ @CallerSensitive public static Lookup lookup() { return new Lookup(Reflection.getCallerClass()); } /** * Returns a {@link Lookup lookup object} which is trusted minimally. * It can only be used to create method handles to * publicly accessible fields and methods. *

* As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class} * of this lookup object will be {@link java.lang.Object}. *

* The lookup class can be changed to any other class {@code C} using an expression of the form * {@linkplain Lookup#in publicLookup().in(C.class)}. * Since all classes have equal access to public names, * such a change would confer no new access rights. */ public static Lookup publicLookup() { return Lookup.PUBLIC_LOOKUP; } /** * A lookup object is a factory for creating method handles, * when the creation requires access checking. * Method handles do not perform * access checks when they are called, but rather when they are created. * Therefore, method handle access * restrictions must be enforced when a method handle is created. * The caller class against which those restrictions are enforced * is known as the {@linkplain #lookupClass lookup class}. *

* A lookup class which needs to create method handles will call * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself. * When the {@code Lookup} factory object is created, the identity of the lookup class is * determined, and securely stored in the {@code Lookup} object. * The lookup class (or its delegates) may then use factory methods * on the {@code Lookup} object to create method handles for access-checked members. * This includes all methods, constructors, and fields which are allowed to the lookup class, * even private ones. *

* The factory methods on a {@code Lookup} object correspond to all major * use cases for methods, constructors, and fields. * Here is a summary of the correspondence between these factory methods and * the behavior the resulting method handles: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
lookup expressionmemberbehavior
{@linkplain java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}FT f;(T) this.f;
{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}static
FT f;
(T) C.f;
{@linkplain java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}FT f;this.f = x;
{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}static
FT f;
C.f = arg;
{@linkplain java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}T m(A*);(T) this.m(arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}static
T m(A*);
(T) C.m(arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}T m(A*);(T) super.m(arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}C(A*);(T) new C(arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}(static)?
FT f;
(FT) aField.get(thisOrNull);
{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}(static)?
FT f;
aField.set(thisOrNull, arg);
{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}(static)?
T m(A*);
(T) aMethod.invoke(thisOrNull, arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}C(A*);(C) aConstructor.newInstance(arg*);
{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}(static)?
T m(A*);
(T) aMethod.invoke(thisOrNull, arg*);
*
* Here, the type {@code C} is the class or interface being searched for a member, * documented as a parameter named {@code refc} in the lookup methods. * The method or constructor type {@code MT} is composed from the return type {@code T} * and the sequence of argument types {@code A*}. * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}. * The formal parameter {@code this} stands for the self-reference of type {@code C}; * if it is present, it is always the leading argument to the method handle invocation. * (In the case of some {@code protected} members, {@code this} may be * restricted in type to the lookup class; see below.) * The name {@code arg} stands for all the other method handle arguments. * In the code examples for the Core Reflection API, the name {@code thisOrNull} * stands for a null reference if the accessed method or field is static, * and {@code this} otherwise. * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand * for reflective objects corresponding to the given members. *

* In cases where the given member is of variable arity (i.e., a method or constructor) * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}. * In all other cases, the returned method handle will be of fixed arity. *

* The equivalence between looked-up method handles and underlying * class members can break down in a few ways: *

* *

Access checking

* Access checks are applied in the factory methods of {@code Lookup}, * when a method handle is created. * This is a key difference from the Core Reflection API, since * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} * performs access checking against every caller, on every call. *

* All access checks start from a {@code Lookup} object, which * compares its recorded lookup class against all requests to * create method handles. * A single {@code Lookup} object can be used to create any number * of access-checked method handles, all checked against a single * lookup class. *

* A {@code Lookup} object can be shared with other trusted code, * such as a metaobject protocol. * A shared {@code Lookup} object delegates the capability * to create method handles on private members of the lookup class. * Even if privileged code uses the {@code Lookup} object, * the access checking is confined to the privileges of the * original lookup class. *

* A lookup can fail, because * the containing class is not accessible to the lookup class, or * because the desired class member is missing, or because the * desired class member is not accessible to the lookup class. * In any of these cases, a {@code ReflectiveOperationException} will be * thrown from the attempted lookup. The exact class will be one of * the following: *

*

* In general, the conditions under which a method handle may be * looked up for a method {@code M} are exactly equivalent to the conditions * under which the lookup class could have compiled and resolved a call to {@code M}. * And the effect of invoking the method handle resulting from the lookup * is exactly equivalent to executing the compiled and resolved call to {@code M}. * The same point is true of fields and constructors. *

* If the desired member is {@code protected}, the usual JVM rules apply, * including the requirement that the lookup class must be either be in the * same package as the desired member, or must inherit that member. * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.) * In addition, if the desired member is a non-static field or method * in a different package, the resulting method handle may only be applied * to objects of the lookup class or one of its subclasses. * This requirement is enforced by narrowing the type of the leading * {@code this} parameter from {@code C} * (which will necessarily be a superclass of the lookup class) * to the lookup class itself. *

* In some cases, access between nested classes is obtained by the Java compiler by creating * an wrapper method to access a private method of another class * in the same top-level declaration. * For example, a nested class {@code C.D} * can access private members within other related classes such as * {@code C}, {@code C.D.E}, or {@code C.B}, * but the Java compiler may need to generate wrapper methods in * those related classes. In such cases, a {@code Lookup} object on * {@code C.E} would be unable to those private members. * A workaround for this limitation is the {@link Lookup#in Lookup.in} method, * which can transform a lookup on {@code C.E} into one on any of those other * classes, without special elevation of privilege. *

* Although bytecode instructions can only refer to classes in * a related class loader, this API can search for methods in any * class, as long as a reference to its {@code Class} object is * available. Such cross-loader references are also possible with the * Core Reflection API, and are impossible to bytecode instructions * such as {@code invokestatic} or {@code getfield}. * There is a {@linkplain java.lang.SecurityManager security manager API} * to allow applications to check such cross-loader references. * These checks apply to both the {@code MethodHandles.Lookup} API * and the Core Reflection API * (as found on {@link java.lang.Class Class}). *

* Access checks only apply to named and reflected methods, * constructors, and fields. * Other method handle creation methods, such as * {@link MethodHandle#asType MethodHandle.asType}, * do not require any access checks, and are done * with static methods of {@link MethodHandles}, * independently of any {@code Lookup} object. * *

Security manager interactions

* * If a security manager is present, member lookups are subject to * additional checks. * From one to four calls are made to the security manager. * Any of these calls can refuse access by throwing a * {@link java.lang.SecurityException SecurityException}. * Define {@code smgr} as the security manager, * {@code refc} as the containing class in which the member * is being sought, and {@code defc} as the class in which the * member is actually defined. * The calls are made according to the following rules: * */ public static final class Lookup { /** The class on behalf of whom the lookup is being performed. */ private final Class lookupClass; /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */ private final int allowedModes; /** A single-bit mask representing {@code public} access, * which may contribute to the result of {@link #lookupModes lookupModes}. * The value, {@code 0x01}, happens to be the same as the value of the * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}. */ public static final int PUBLIC = Modifier.PUBLIC; /** A single-bit mask representing {@code private} access, * which may contribute to the result of {@link #lookupModes lookupModes}. * The value, {@code 0x02}, happens to be the same as the value of the * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}. */ public static final int PRIVATE = Modifier.PRIVATE; /** A single-bit mask representing {@code protected} access, * which may contribute to the result of {@link #lookupModes lookupModes}. * The value, {@code 0x04}, happens to be the same as the value of the * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}. */ public static final int PROTECTED = Modifier.PROTECTED; /** A single-bit mask representing {@code package} access (default access), * which may contribute to the result of {@link #lookupModes lookupModes}. * The value is {@code 0x08}, which does not correspond meaningfully to * any particular {@linkplain java.lang.reflect.Modifier modifier bit}. */ public static final int PACKAGE = Modifier.STATIC; private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE); private static final int TRUSTED = -1; private static int fixmods(int mods) { mods &= (ALL_MODES - PACKAGE); return (mods != 0) ? mods : PACKAGE; } /** Tells which class is performing the lookup. It is this class against * which checks are performed for visibility and access permissions. *

* The class implies a maximum level of access permission, * but the permissions may be additionally limited by the bitmask * {@link #lookupModes lookupModes}, which controls whether non-public members * can be accessed. */ public Class lookupClass() { return lookupClass; } // This is just for calling out to MethodHandleImpl. private Class lookupClassOrNull() { return (allowedModes == TRUSTED) ? null : lookupClass; } /** Tells which access-protection classes of members this lookup object can produce. * The result is a bit-mask of the bits * {@linkplain #PUBLIC PUBLIC (0x01)}, * {@linkplain #PRIVATE PRIVATE (0x02)}, * {@linkplain #PROTECTED PROTECTED (0x04)}, * and {@linkplain #PACKAGE PACKAGE (0x08)}. *

* A freshly-created lookup object * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class} * has all possible bits set, since the caller class can access all its own members. * A lookup object on a new lookup class * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object} * may have some mode bits set to zero. * The purpose of this is to restrict access via the new lookup object, * so that it can access only names which can be reached by the original * lookup object, and also by the new lookup class. */ public int lookupModes() { return allowedModes & ALL_MODES; } /** Embody the current class (the lookupClass) as a lookup class * for method handle creation. * Must be called by from a method in this package, * which in turn is called by a method not in this package. *

* Also, don't make it private, lest javac interpose * an access$N method. */ Lookup(Class lookupClass) { this(lookupClass, ALL_MODES); checkUnprivilegedlookupClass(lookupClass); } private Lookup(Class lookupClass, int allowedModes) { this.lookupClass = lookupClass; this.allowedModes = allowedModes; } /** * Creates a lookup on the specified new lookup class. * The resulting object will report the specified * class as its own {@link #lookupClass lookupClass}. *

* However, the resulting {@code Lookup} object is guaranteed * to have no more access capabilities than the original. * In particular, access capabilities can be lost as follows:

* * @param requestedLookupClass the desired lookup class for the new lookup object * @return a lookup object which reports the desired lookup class * @throws NullPointerException if the argument is null */ public Lookup in(Class requestedLookupClass) { requestedLookupClass.getClass(); // null check if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all return new Lookup(requestedLookupClass, ALL_MODES); if (requestedLookupClass == this.lookupClass) return this; // keep same capabilities int newModes = (allowedModes & (ALL_MODES & ~PROTECTED)); if ((newModes & PACKAGE) != 0 && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) { newModes &= ~(PACKAGE|PRIVATE); } // Allow nestmate lookups to be created without special privilege: if ((newModes & PRIVATE) != 0 && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) { newModes &= ~PRIVATE; } if ((newModes & PUBLIC) != 0 && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) { // The requested class it not accessible from the lookup class. // No permissions. newModes = 0; } checkUnprivilegedlookupClass(requestedLookupClass); return new Lookup(requestedLookupClass, newModes); } // Make sure outer class is initialized first. static { IMPL_NAMES.getClass(); } /** Version of lookup which is trusted minimally. * It can only be used to create method handles to * publicly accessible members. */ static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC); /** Package-private version of lookup which is trusted. */ static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED); private static void checkUnprivilegedlookupClass(Class lookupClass) { String name = lookupClass.getName(); if (name.startsWith("java.lang.invoke.")) throw newIllegalArgumentException("illegal lookupClass: "+lookupClass); } /** * Displays the name of the class from which lookups are to be made. * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.) * If there are restrictions on the access permitted to this lookup, * this is indicated by adding a suffix to the class name, consisting * of a slash and a keyword. The keyword represents the strongest * allowed access, and is chosen as follows: * * If none of the above cases apply, it is the case that full * access (public, package, private, and protected) is allowed. * In this case, no suffix is added. * This is true only of an object obtained originally from * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}. * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in} * always have restricted access, and will display a suffix. *

* (It may seem strange that protected access should be * stronger than private access. Viewed independently from * package access, protected access is the first to be lost, * because it requires a direct subclass relationship between * caller and callee.) * @see #in */ @Override public String toString() { String cname = lookupClass.getName(); switch (allowedModes) { case 0: // no privileges return cname + "/noaccess"; case PUBLIC: return cname + "/public"; case PUBLIC|PACKAGE: return cname + "/package"; case ALL_MODES & ~PROTECTED: return cname + "/private"; case ALL_MODES: return cname; case TRUSTED: return "/trusted"; // internal only; not exported default: // Should not happen, but it's a bitfield... cname = cname + "/" + Integer.toHexString(allowedModes); assert(false) : cname; return cname; } } /** * Produces a method handle for a static method. * The type of the method handle will be that of the method. * (Since static methods do not take receivers, there is no * additional receiver argument inserted into the method handle type, * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.) * The method and all its argument types must be accessible to the lookup class. * If the method's class has not yet been initialized, that is done * immediately, before the method handle is returned. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. * @param refc the class from which the method is accessed * @param name the name of the method * @param type the type of the method * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails, * or if the method is not {@code static}, * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findStatic(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { MemberName method = resolveOrFail(REF_invokeStatic, refc, name, type); checkSecurityManager(refc, method); return getDirectMethod(REF_invokeStatic, refc, method, findBoundCallerClass(method)); } /** * Produces a method handle for a virtual method. * The type of the method handle will be that of the method, * with the receiver type (usually {@code refc}) prepended. * The method and all its argument types must be accessible to the lookup class. *

* When called, the handle will treat the first argument as a receiver * and dispatch on the receiver's type to determine which method * implementation to enter. * (The dispatching action is identical with that performed by an * {@code invokevirtual} or {@code invokeinterface} instruction.) *

* The first argument will be of type {@code refc} if the lookup * class has full privileges to access the member. Otherwise * the member must be {@code protected} and the first argument * will be restricted in type to the lookup class. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. *

* Because of the general equivalence between {@code invokevirtual} * instructions and method handles produced by {@code findVirtual}, * if the class is {@code MethodHandle} and the name string is * {@code invokeExact} or {@code invoke}, the resulting * method handle is equivalent to one produced by * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker} * with the same {@code type} argument. * * @param refc the class or interface from which the method is accessed * @param name the name of the method * @param type the type of the method, with the receiver argument omitted * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails, * or if the method is {@code static} * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findVirtual(Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { if (refc == MethodHandle.class) { MethodHandle mh = findVirtualForMH(name, type); if (mh != null) return mh; } byte refKind = (refc.isInterface() ? REF_invokeInterface : REF_invokeVirtual); MemberName method = resolveOrFail(refKind, refc, name, type); checkSecurityManager(refc, method); return getDirectMethod(refKind, refc, method, findBoundCallerClass(method)); } private MethodHandle findVirtualForMH(String name, MethodType type) { // these names require special lookups because of the implicit MethodType argument if ("invoke".equals(name)) return invoker(type); if ("invokeExact".equals(name)) return exactInvoker(type); return null; } /** * Produces a method handle which creates an object and initializes it, using * the constructor of the specified type. * The parameter types of the method handle will be those of the constructor, * while the return type will be a reference to the constructor's class. * The constructor and all its argument types must be accessible to the lookup class. * If the constructor's class has not yet been initialized, that is done * immediately, before the method handle is returned. *

* Note: The requested type must have a return type of {@code void}. * This is consistent with the JVM's treatment of constructor type descriptors. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the constructor's variable arity modifier bit ({@code 0x0080}) is set. * @param refc the class or interface from which the method is accessed * @param type the type of the method, with the receiver argument omitted, and a void return type * @return the desired method handle * @throws NoSuchMethodException if the constructor does not exist * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findConstructor(Class refc, MethodType type) throws NoSuchMethodException, IllegalAccessException { String name = ""; MemberName ctor = resolveOrFail(REF_newInvokeSpecial, refc, name, type); checkSecurityManager(refc, ctor); return getDirectConstructor(refc, ctor); } /** * Produces an early-bound method handle for a virtual method, * as if called from an {@code invokespecial} * instruction from {@code caller}. * The type of the method handle will be that of the method, * with a suitably restricted receiver type (such as {@code caller}) prepended. * The method and all its argument types must be accessible * to the caller. *

* When called, the handle will treat the first argument as a receiver, * but will not dispatch on the receiver's type. * (This direct invocation action is identical with that performed by an * {@code invokespecial} instruction.) *

* If the explicitly specified caller class is not identical with the * lookup class, or if this lookup object does not have private access * privileges, the access fails. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. * @param refc the class or interface from which the method is accessed * @param name the name of the method (which must not be "<init>") * @param type the type of the method, with the receiver argument omitted * @param specialCaller the proposed calling class to perform the {@code invokespecial} * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findSpecial(Class refc, String name, MethodType type, Class specialCaller) throws NoSuchMethodException, IllegalAccessException { checkSpecialCaller(specialCaller); Lookup specialLookup = this.in(specialCaller); MemberName method = specialLookup.resolveOrFail(REF_invokeSpecial, refc, name, type); checkSecurityManager(refc, method); return specialLookup.getDirectMethod(REF_invokeSpecial, refc, method, findBoundCallerClass(method)); } /** * Produces a method handle giving read access to a non-static field. * The type of the method handle will have a return type of the field's * value type. * The method handle's single argument will be the instance containing * the field. * Access checking is performed immediately on behalf of the lookup class. * @param refc the class or interface from which the method is accessed * @param name the field's name * @param type the field's type * @return a method handle which can load values from the field * @throws NoSuchFieldException if the field does not exist * @throws IllegalAccessException if access checking fails, or if the field is {@code static} * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException { MemberName field = resolveOrFail(REF_getField, refc, name, type); checkSecurityManager(refc, field); return getDirectField(REF_getField, refc, field); } /** * Produces a method handle giving write access to a non-static field. * The type of the method handle will have a void return type. * The method handle will take two arguments, the instance containing * the field, and the value to be stored. * The second argument will be of the field's value type. * Access checking is performed immediately on behalf of the lookup class. * @param refc the class or interface from which the method is accessed * @param name the field's name * @param type the field's type * @return a method handle which can store values into the field * @throws NoSuchFieldException if the field does not exist * @throws IllegalAccessException if access checking fails, or if the field is {@code static} * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException { MemberName field = resolveOrFail(REF_putField, refc, name, type); checkSecurityManager(refc, field); return getDirectField(REF_putField, refc, field); } /** * Produces a method handle giving read access to a static field. * The type of the method handle will have a return type of the field's * value type. * The method handle will take no arguments. * Access checking is performed immediately on behalf of the lookup class. * @param refc the class or interface from which the method is accessed * @param name the field's name * @param type the field's type * @return a method handle which can load values from the field * @throws NoSuchFieldException if the field does not exist * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findStaticGetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException { MemberName field = resolveOrFail(REF_getStatic, refc, name, type); checkSecurityManager(refc, field); return getDirectField(REF_getStatic, refc, field); } /** * Produces a method handle giving write access to a static field. * The type of the method handle will have a void return type. * The method handle will take a single * argument, of the field's value type, the value to be stored. * Access checking is performed immediately on behalf of the lookup class. * @param refc the class or interface from which the method is accessed * @param name the field's name * @param type the field's type * @return a method handle which can store values into the field * @throws NoSuchFieldException if the field does not exist * @throws IllegalAccessException if access checking fails, or if the field is not {@code static} * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle findStaticSetter(Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException { MemberName field = resolveOrFail(REF_putStatic, refc, name, type); checkSecurityManager(refc, field); return getDirectField(REF_putStatic, refc, field); } /** * Produces an early-bound method handle for a non-static method. * The receiver must have a supertype {@code defc} in which a method * of the given name and type is accessible to the lookup class. * The method and all its argument types must be accessible to the lookup class. * The type of the method handle will be that of the method, * without any insertion of an additional receiver parameter. * The given receiver will be bound into the method handle, * so that every call to the method handle will invoke the * requested method on the given receiver. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set * and the trailing array argument is not the only argument. * (If the trailing array argument is the only argument, * the given receiver value will be bound to it.) *

* This is equivalent to the following code: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle mh0 = lookup().{@link #findVirtual findVirtual}(defc, name, type);
MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
MethodType mt1 = mh1.type();
if (mh0.isVarargsCollector())
  mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
return mh1;
         * 
* where {@code defc} is either {@code receiver.getClass()} or a super * type of that class, in which the requested method is accessible * to the lookup class. * (Note that {@code bindTo} does not preserve variable arity.) * @param receiver the object from which the method is accessed * @param name the name of the method * @param type the type of the method, with the receiver argument omitted * @return the desired method handle * @throws NoSuchMethodException if the method does not exist * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @exception SecurityException if a security manager is present and it * refuses access * @throws NullPointerException if any argument is null */ public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { Class refc = receiver.getClass(); // may get NPE MemberName method = resolveOrFail(REF_invokeSpecial, refc, name, type); checkSecurityManager(refc, method); MethodHandle mh = getDirectMethodNoRestrict(REF_invokeSpecial, refc, method, findBoundCallerClass(method)); return mh.bindReceiver(receiver).setVarargs(method); } /** * Makes a direct method handle to m, if the lookup class has permission. * If m is non-static, the receiver argument is treated as an initial argument. * If m is virtual, overriding is respected on every call. * Unlike the Core Reflection API, exceptions are not wrapped. * The type of the method handle will be that of the method, * with the receiver type prepended (but only if it is non-static). * If the method's {@code accessible} flag is not set, * access checking is performed immediately on behalf of the lookup class. * If m is not public, do not share the resulting handle with untrusted parties. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. * @param m the reflected method * @return a method handle which can invoke the reflected method * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @throws NullPointerException if the argument is null */ public MethodHandle unreflect(Method m) throws IllegalAccessException { MemberName method = new MemberName(m); byte refKind = method.getReferenceKind(); if (refKind == REF_invokeSpecial) refKind = REF_invokeVirtual; assert(method.isMethod()); Lookup lookup = m.isAccessible() ? IMPL_LOOKUP : this; return lookup.getDirectMethod(refKind, method.getDeclaringClass(), method, findBoundCallerClass(method)); } /** * Produces a method handle for a reflected method. * It will bypass checks for overriding methods on the receiver, * as if by a {@code invokespecial} instruction from within the {@code specialCaller}. * The type of the method handle will be that of the method, * with the special caller type prepended (and not the receiver of the method). * If the method's {@code accessible} flag is not set, * access checking is performed immediately on behalf of the lookup class, * as if {@code invokespecial} instruction were being linked. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the method's variable arity modifier bit ({@code 0x0080}) is set. * @param m the reflected method * @param specialCaller the class nominally calling the method * @return a method handle which can invoke the reflected method * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @throws NullPointerException if any argument is null */ public MethodHandle unreflectSpecial(Method m, Class specialCaller) throws IllegalAccessException { checkSpecialCaller(specialCaller); Lookup specialLookup = this.in(specialCaller); MemberName method = new MemberName(m, true); assert(method.isMethod()); // ignore m.isAccessible: this is a new kind of access return specialLookup.getDirectMethod(REF_invokeSpecial, method.getDeclaringClass(), method, findBoundCallerClass(method)); } /** * Produces a method handle for a reflected constructor. * The type of the method handle will be that of the constructor, * with the return type changed to the declaring class. * The method handle will perform a {@code newInstance} operation, * creating a new instance of the constructor's class on the * arguments passed to the method handle. *

* If the constructor's {@code accessible} flag is not set, * access checking is performed immediately on behalf of the lookup class. *

* The returned method handle will have * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if * the constructor's variable arity modifier bit ({@code 0x0080}) is set. * @param c the reflected constructor * @return a method handle which can invoke the reflected constructor * @throws IllegalAccessException if access checking fails * or if the method's variable arity modifier bit * is set and {@code asVarargsCollector} fails * @throws NullPointerException if the argument is null */ @SuppressWarnings("rawtypes") // Will be Constructor after JSR 292 MR public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException { MemberName ctor = new MemberName(c); assert(ctor.isConstructor()); Lookup lookup = c.isAccessible() ? IMPL_LOOKUP : this; return lookup.getDirectConstructor(ctor.getDeclaringClass(), ctor); } /** * Produces a method handle giving read access to a reflected field. * The type of the method handle will have a return type of the field's * value type. * If the field is static, the method handle will take no arguments. * Otherwise, its single argument will be the instance containing * the field. * If the field's {@code accessible} flag is not set, * access checking is performed immediately on behalf of the lookup class. * @param f the reflected field * @return a method handle which can load values from the reflected field * @throws IllegalAccessException if access checking fails * @throws NullPointerException if the argument is null */ public MethodHandle unreflectGetter(Field f) throws IllegalAccessException { return unreflectField(f, false); } private MethodHandle unreflectField(Field f, boolean isSetter) throws IllegalAccessException { MemberName field = new MemberName(f, isSetter); assert(isSetter ? MethodHandleNatives.refKindIsSetter(field.getReferenceKind()) : MethodHandleNatives.refKindIsGetter(field.getReferenceKind())); Lookup lookup = f.isAccessible() ? IMPL_LOOKUP : this; return lookup.getDirectField(field.getReferenceKind(), f.getDeclaringClass(), field); } /** * Produces a method handle giving write access to a reflected field. * The type of the method handle will have a void return type. * If the field is static, the method handle will take a single * argument, of the field's value type, the value to be stored. * Otherwise, the two arguments will be the instance containing * the field, and the value to be stored. * If the field's {@code accessible} flag is not set, * access checking is performed immediately on behalf of the lookup class. * @param f the reflected field * @return a method handle which can store values into the reflected field * @throws IllegalAccessException if access checking fails * @throws NullPointerException if the argument is null */ public MethodHandle unreflectSetter(Field f) throws IllegalAccessException { return unreflectField(f, true); } /// Helper methods, all package-private. MemberName resolveOrFail(byte refKind, Class refc, String name, Class type) throws NoSuchFieldException, IllegalAccessException { checkSymbolicClass(refc); // do this before attempting to resolve name.getClass(); type.getClass(); // NPE return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), NoSuchFieldException.class); } MemberName resolveOrFail(byte refKind, Class refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException { checkSymbolicClass(refc); // do this before attempting to resolve name.getClass(); type.getClass(); // NPE return IMPL_NAMES.resolveOrFail(refKind, new MemberName(refc, name, type, refKind), lookupClassOrNull(), NoSuchMethodException.class); } void checkSymbolicClass(Class refc) throws IllegalAccessException { Class caller = lookupClassOrNull(); if (caller != null && !VerifyAccess.isClassAccessible(refc, caller, allowedModes)) throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this); } /** * Find my trustable caller class if m is a caller sensitive method. * If this lookup object has private access, then the caller class is the lookupClass. * Otherwise, if m is caller-sensitive, throw IllegalAccessException. */ Class findBoundCallerClass(MemberName m) throws IllegalAccessException { Class callerClass = null; if (MethodHandleNatives.isCallerSensitive(m)) { // Only full-power lookup is allowed to resolve caller-sensitive methods if (isFullPowerLookup()) { callerClass = lookupClass; } else { throw new IllegalAccessException("Attempt to lookup caller-sensitive method using restricted lookup object"); } } return callerClass; } private boolean isFullPowerLookup() { return (allowedModes & PRIVATE) != 0; } /** * Determine whether a security manager has an overridden * SecurityManager.checkMemberAccess method. */ private boolean isCheckMemberAccessOverridden(SecurityManager sm) { final Class cls = sm.getClass(); if (cls == SecurityManager.class) return false; try { return cls.getMethod("checkMemberAccess", Class.class, int.class). getDeclaringClass() != SecurityManager.class; } catch (NoSuchMethodException e) { throw new InternalError("should not reach here"); } } /** * Perform necessary access checks. * This function performs stack walk magic: do not refactor it. */ void checkSecurityManager(Class refc, MemberName m) { SecurityManager smgr = System.getSecurityManager(); if (smgr == null) return; if (allowedModes == TRUSTED) return; final boolean overridden = isCheckMemberAccessOverridden(smgr); // Step 1: { // Default policy is to allow Member.PUBLIC; no need to check // permission if SecurityManager is the default implementation final int which = Member.PUBLIC; final Class clazz = refc; if (overridden) { // Don't refactor; otherwise break the stack depth for // checkMemberAccess of subclasses of SecurityManager as specified. smgr.checkMemberAccess(clazz, which); } } // Step 2: if (!isFullPowerLookup() || !VerifyAccess.classLoaderIsAncestor(lookupClass, refc)) { ReflectUtil.checkPackageAccess(refc); } // Step 3: if (m.isPublic()) return; Class defc = m.getDeclaringClass(); { // Inline SecurityManager.checkMemberAccess final int which = Member.DECLARED; final Class clazz = defc; if (!overridden) { if (!isFullPowerLookup()) { smgr.checkPermission(SecurityConstants.CHECK_MEMBER_ACCESS_PERMISSION); } } else { // Don't refactor; otherwise break the stack depth for // checkMemberAccess of subclasses of SecurityManager as specified. smgr.checkMemberAccess(clazz, which); } } // Step 4: if (defc != refc) { ReflectUtil.checkPackageAccess(defc); } } void checkMethod(byte refKind, Class refc, MemberName m) throws IllegalAccessException { boolean wantStatic = (refKind == REF_invokeStatic); String message; if (m.isConstructor()) message = "expected a method, not a constructor"; else if (!m.isMethod()) message = "expected a method"; else if (wantStatic != m.isStatic()) message = wantStatic ? "expected a static method" : "expected a non-static method"; else { checkAccess(refKind, refc, m); return; } throw m.makeAccessException(message, this); } void checkField(byte refKind, Class refc, MemberName m) throws IllegalAccessException { boolean wantStatic = !MethodHandleNatives.refKindHasReceiver(refKind); String message; if (wantStatic != m.isStatic()) message = wantStatic ? "expected a static field" : "expected a non-static field"; else { checkAccess(refKind, refc, m); return; } throw m.makeAccessException(message, this); } void checkAccess(byte refKind, Class refc, MemberName m) throws IllegalAccessException { assert(m.referenceKindIsConsistentWith(refKind) && MethodHandleNatives.refKindIsValid(refKind) && (MethodHandleNatives.refKindIsField(refKind) == m.isField())); int allowedModes = this.allowedModes; if (allowedModes == TRUSTED) return; int mods = m.getModifiers(); if (Modifier.isFinal(mods) && MethodHandleNatives.refKindIsSetter(refKind)) throw m.makeAccessException("unexpected set of a final field", this); if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0) return; // common case int requestedModes = fixmods(mods); // adjust 0 => PACKAGE if ((requestedModes & allowedModes) != 0) { if (VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(), mods, lookupClass(), allowedModes)) return; } else { // Protected members can also be checked as if they were package-private. if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0 && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass())) return; } throw m.makeAccessException(accessFailedMessage(refc, m), this); } String accessFailedMessage(Class refc, MemberName m) { Class defc = m.getDeclaringClass(); int mods = m.getModifiers(); // check the class first: boolean classOK = (Modifier.isPublic(defc.getModifiers()) && (defc == refc || Modifier.isPublic(refc.getModifiers()))); if (!classOK && (allowedModes & PACKAGE) != 0) { classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) && (defc == refc || VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES))); } if (!classOK) return "class is not public"; if (Modifier.isPublic(mods)) return "access to public member failed"; // (how?) if (Modifier.isPrivate(mods)) return "member is private"; if (Modifier.isProtected(mods)) return "member is protected"; return "member is private to package"; } private static final boolean ALLOW_NESTMATE_ACCESS = false; private void checkSpecialCaller(Class specialCaller) throws IllegalAccessException { int allowedModes = this.allowedModes; if (allowedModes == TRUSTED) return; if ((allowedModes & PRIVATE) == 0 || (specialCaller != lookupClass() && !(ALLOW_NESTMATE_ACCESS && VerifyAccess.isSamePackageMember(specialCaller, lookupClass())))) throw new MemberName(specialCaller). makeAccessException("no private access for invokespecial", this); } private boolean restrictProtectedReceiver(MemberName method) { // The accessing class only has the right to use a protected member // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc. if (!method.isProtected() || method.isStatic() || allowedModes == TRUSTED || method.getDeclaringClass() == lookupClass() || VerifyAccess.isSamePackage(method.getDeclaringClass(), lookupClass()) || (ALLOW_NESTMATE_ACCESS && VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass()))) return false; return true; } private MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class caller) throws IllegalAccessException { assert(!method.isStatic()); // receiver type of mh is too wide; narrow to caller if (!method.getDeclaringClass().isAssignableFrom(caller)) { throw method.makeAccessException("caller class must be a subclass below the method", caller); } MethodType rawType = mh.type(); if (rawType.parameterType(0) == caller) return mh; MethodType narrowType = rawType.changeParameterType(0, caller); return mh.viewAsType(narrowType); } private MethodHandle getDirectMethod(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException { return getDirectMethodCommon(refKind, refc, method, (refKind == REF_invokeSpecial || (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(method))), callerClass); } private MethodHandle getDirectMethodNoRestrict(byte refKind, Class refc, MemberName method, Class callerClass) throws IllegalAccessException { return getDirectMethodCommon(refKind, refc, method, false, callerClass); } private MethodHandle getDirectMethodCommon(byte refKind, Class refc, MemberName method, boolean doRestrict, Class callerClass) throws IllegalAccessException { checkMethod(refKind, refc, method); if (method.isMethodHandleInvoke()) return fakeMethodHandleInvoke(method); Class refcAsSuper; if (refKind == REF_invokeSpecial && refc != lookupClass() && refc != (refcAsSuper = lookupClass().getSuperclass()) && refc.isAssignableFrom(lookupClass())) { assert(!method.getName().equals("")); // not this code path // Per JVMS 6.5, desc. of invokespecial instruction: // If the method is in a superclass of the LC, // and if our original search was above LC.super, // repeat the search (symbolic lookup) from LC.super. // FIXME: MemberName.resolve should handle this instead. MemberName m2 = new MemberName(refcAsSuper, method.getName(), method.getMethodType(), REF_invokeSpecial); m2 = IMPL_NAMES.resolveOrNull(refKind, m2, lookupClassOrNull()); if (m2 == null) throw new InternalError(method.toString()); method = m2; refc = refcAsSuper; // redo basic checks checkMethod(refKind, refc, method); } MethodHandle mh = DirectMethodHandle.make(refc, method); mh = maybeBindCaller(method, mh, callerClass); mh = mh.setVarargs(method); if (doRestrict) mh = restrictReceiver(method, mh, lookupClass()); return mh; } private MethodHandle fakeMethodHandleInvoke(MemberName method) { return throwException(method.getReturnType(), UnsupportedOperationException.class); } private MethodHandle maybeBindCaller(MemberName method, MethodHandle mh, Class callerClass) throws IllegalAccessException { if (allowedModes == TRUSTED || !MethodHandleNatives.isCallerSensitive(method)) return mh; Class hostClass = lookupClass; if ((allowedModes & PRIVATE) == 0) // caller must use full-power lookup hostClass = callerClass; // callerClass came from a security manager style stack walk MethodHandle cbmh = MethodHandleImpl.bindCaller(mh, hostClass); // Note: caller will apply varargs after this step happens. return cbmh; } private MethodHandle getDirectField(byte refKind, Class refc, MemberName field) throws IllegalAccessException { checkField(refKind, refc, field); MethodHandle mh = DirectMethodHandle.make(refc, field); boolean doRestrict = (MethodHandleNatives.refKindHasReceiver(refKind) && restrictProtectedReceiver(field)); if (doRestrict) mh = restrictReceiver(field, mh, lookupClass()); return mh; } private MethodHandle getDirectConstructor(Class refc, MemberName ctor) throws IllegalAccessException { assert(ctor.isConstructor()); checkAccess(REF_newInvokeSpecial, refc, ctor); assert(!MethodHandleNatives.isCallerSensitive(ctor)); // maybeBindCaller not relevant here return DirectMethodHandle.make(ctor).setVarargs(ctor); } /** Hook called from the JVM (via MethodHandleNatives) to link MH constants: */ /*non-public*/ MethodHandle linkMethodHandleConstant(byte refKind, Class defc, String name, Object type) throws ReflectiveOperationException { MemberName resolved = null; if (type instanceof MemberName) { resolved = (MemberName) type; if (!resolved.isResolved()) throw new InternalError("unresolved MemberName"); assert(name == null || name.equals(resolved.getName())); } if (MethodHandleNatives.refKindIsField(refKind)) { MemberName field = (resolved != null) ? resolved : resolveOrFail(refKind, defc, name, (Class) type); return getDirectField(refKind, defc, field); } else if (MethodHandleNatives.refKindIsMethod(refKind)) { MemberName method = (resolved != null) ? resolved : resolveOrFail(refKind, defc, name, (MethodType) type); return getDirectMethod(refKind, defc, method, lookupClass); } else if (refKind == REF_newInvokeSpecial) { assert(name == null || name.equals("")); MemberName ctor = (resolved != null) ? resolved : resolveOrFail(REF_newInvokeSpecial, defc, name, (MethodType) type); return getDirectConstructor(defc, ctor); } // oops throw new ReflectiveOperationException("bad MethodHandle constant #"+refKind+" "+name+" : "+type); } } /** * Produces a method handle giving read access to elements of an array. * The type of the method handle will have a return type of the array's * element type. Its first argument will be the array type, * and the second will be {@code int}. * @param arrayClass an array type * @return a method handle which can load values from the given array type * @throws NullPointerException if the argument is null * @throws IllegalArgumentException if arrayClass is not an array type */ public static MethodHandle arrayElementGetter(Class arrayClass) throws IllegalArgumentException { return MethodHandleImpl.makeArrayElementAccessor(arrayClass, false); } /** * Produces a method handle giving write access to elements of an array. * The type of the method handle will have a void return type. * Its last argument will be the array's element type. * The first and second arguments will be the array type and int. * @return a method handle which can store values into the array type * @throws NullPointerException if the argument is null * @throws IllegalArgumentException if arrayClass is not an array type */ public static MethodHandle arrayElementSetter(Class arrayClass) throws IllegalArgumentException { return MethodHandleImpl.makeArrayElementAccessor(arrayClass, true); } /// method handle invocation (reflective style) /** * Produces a method handle which will invoke any method handle of the * given {@code type}, with a given number of trailing arguments replaced by * a single trailing {@code Object[]} array. * The resulting invoker will be a method handle with the following * arguments: *

*

* The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with * the indicated {@code type}. * That is, if the target is exactly of the given {@code type}, it will behave * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType} * is used to convert the target to the required {@code type}. *

* The type of the returned invoker will not be the given {@code type}, but rather * will have all parameters except the first {@code leadingArgCount} * replaced by a single array of type {@code Object[]}, which will be * the final parameter. *

* Before invoking its target, the invoker will spread the final array, apply * reference casts as necessary, and unbox and widen primitive arguments. *

* This method is equivalent to the following code (though it may be more efficient): *

MethodHandle invoker = MethodHandles.invoker(type);
int spreadArgCount = type.parameterCount() - leadingArgCount;
invoker = invoker.asSpreader(Object[].class, spreadArgCount);
return invoker;
     * 
*

* This method throws no reflective or security exceptions. * @param type the desired target type * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target * @return a method handle suitable for invoking any method handle of the given type * @throws NullPointerException if {@code type} is null * @throws IllegalArgumentException if {@code leadingArgCount} is not in * the range from 0 to {@code type.parameterCount()} inclusive */ static public MethodHandle spreadInvoker(MethodType type, int leadingArgCount) { if (leadingArgCount < 0 || leadingArgCount > type.parameterCount()) throw new IllegalArgumentException("bad argument count "+leadingArgCount); return type.invokers().spreadInvoker(leadingArgCount); } /** * Produces a special invoker method handle which can be used to * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}. * The resulting invoker will have a type which is * exactly equal to the desired type, except that it will accept * an additional leading argument of type {@code MethodHandle}. *

* This method is equivalent to the following code (though it may be more efficient): *

publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
     * 
* *

* Discussion: * Invoker method handles can be useful when working with variable method handles * of unknown types. * For example, to emulate an {@code invokeExact} call to a variable method * handle {@code M}, extract its type {@code T}, * look up the invoker method {@code X} for {@code T}, * and call the invoker method, as {@code X.invoke(T, A...)}. * (It would not work to call {@code X.invokeExact}, since the type {@code T} * is unknown.) * If spreading, collecting, or other argument transformations are required, * they can be applied once to the invoker {@code X} and reused on many {@code M} * method handle values, as long as they are compatible with the type of {@code X}. *

* (Note: The invoker method is not available via the Core Reflection API. * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke} * on the declared {@code invokeExact} or {@code invoke} method will raise an * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.) *

* This method throws no reflective or security exceptions. * @param type the desired target type * @return a method handle suitable for invoking any method handle of the given type */ static public MethodHandle exactInvoker(MethodType type) { return type.invokers().exactInvoker(); } /** * Produces a special invoker method handle which can be used to * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}. * The resulting invoker will have a type which is * exactly equal to the desired type, except that it will accept * an additional leading argument of type {@code MethodHandle}. *

* Before invoking its target, if the target differs from the expected type, * the invoker will apply reference casts as * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}. * Similarly, the return value will be converted as necessary. * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle}, * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}. *

* A {@linkplain MethodType#genericMethodType general method type}, * mentions only {@code Object} arguments and return values. * An invoker for such a type is capable of calling any method handle * of the same arity as the general type. *

* This method is equivalent to the following code (though it may be more efficient): *

publicLookup().findVirtual(MethodHandle.class, "invoke", type)
     * 
*

* This method throws no reflective or security exceptions. * @param type the desired target type * @return a method handle suitable for invoking any method handle convertible to the given type */ static public MethodHandle invoker(MethodType type) { return type.invokers().generalInvoker(); } static /*non-public*/ MethodHandle basicInvoker(MethodType type) { return type.form().basicInvoker(); } /// method handle modification (creation from other method handles) /** * Produces a method handle which adapts the type of the * given method handle to a new type by pairwise argument and return type conversion. * The original type and new type must have the same number of arguments. * The resulting method handle is guaranteed to report a type * which is equal to the desired new type. *

* If the original type and new type are equal, returns target. *

* The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType}, * and some additional conversions are also applied if those conversions fail. * Given types T0, T1, one of the following conversions is applied * if possible, before or instead of any conversions done by {@code asType}: *

* @param target the method handle to invoke after arguments are retyped * @param newType the expected type of the new method handle * @return a method handle which delegates to the target after performing * any necessary argument conversions, and arranges for any * necessary return value conversions * @throws NullPointerException if either argument is null * @throws WrongMethodTypeException if the conversion cannot be made * @see MethodHandle#asType */ public static MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) { if (!target.type().isCastableTo(newType)) { throw new WrongMethodTypeException("cannot explicitly cast "+target+" to "+newType); } return MethodHandleImpl.makePairwiseConvert(target, newType, 2); } /** * Produces a method handle which adapts the calling sequence of the * given method handle to a new type, by reordering the arguments. * The resulting method handle is guaranteed to report a type * which is equal to the desired new type. *

* The given array controls the reordering. * Call {@code #I} the number of incoming parameters (the value * {@code newType.parameterCount()}, and call {@code #O} the number * of outgoing parameters (the value {@code target.type().parameterCount()}). * Then the length of the reordering array must be {@code #O}, * and each element must be a non-negative number less than {@code #I}. * For every {@code N} less than {@code #O}, the {@code N}-th * outgoing argument will be taken from the {@code I}-th incoming * argument, where {@code I} is {@code reorder[N]}. *

* No argument or return value conversions are applied. * The type of each incoming argument, as determined by {@code newType}, * must be identical to the type of the corresponding outgoing parameter * or parameters in the target method handle. * The return type of {@code newType} must be identical to the return * type of the original target. *

* The reordering array need not specify an actual permutation. * An incoming argument will be duplicated if its index appears * more than once in the array, and an incoming argument will be dropped * if its index does not appear in the array. * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments}, * incoming arguments which are not mentioned in the reordering array * are may be any type, as determined only by {@code newType}. *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodType intfn1 = methodType(int.class, int.class);
MethodType intfn2 = methodType(int.class, int.class, int.class);
MethodHandle sub = ... {int x, int y => x-y} ...;
assert(sub.type().equals(intfn2));
MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
assert((int)rsub.invokeExact(1, 100) == 99);
MethodHandle add = ... {int x, int y => x+y} ...;
assert(add.type().equals(intfn2));
MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
assert(twice.type().equals(intfn1));
assert((int)twice.invokeExact(21) == 42);
     * 
* @param target the method handle to invoke after arguments are reordered * @param newType the expected type of the new method handle * @param reorder an index array which controls the reordering * @return a method handle which delegates to the target after it * drops unused arguments and moves and/or duplicates the other arguments * @throws NullPointerException if any argument is null * @throws IllegalArgumentException if the index array length is not equal to * the arity of the target, or if any index array element * not a valid index for a parameter of {@code newType}, * or if two corresponding parameter types in * {@code target.type()} and {@code newType} are not identical, */ public static MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) { checkReorder(reorder, newType, target.type()); return target.permuteArguments(newType, reorder); } private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) { if (newType.returnType() != oldType.returnType()) throw newIllegalArgumentException("return types do not match", oldType, newType); if (reorder.length == oldType.parameterCount()) { int limit = newType.parameterCount(); boolean bad = false; for (int j = 0; j < reorder.length; j++) { int i = reorder[j]; if (i < 0 || i >= limit) { bad = true; break; } Class src = newType.parameterType(i); Class dst = oldType.parameterType(j); if (src != dst) throw newIllegalArgumentException("parameter types do not match after reorder", oldType, newType); } if (!bad) return; } throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder)); } /** * Produces a method handle of the requested return type which returns the given * constant value every time it is invoked. *

* Before the method handle is returned, the passed-in value is converted to the requested type. * If the requested type is primitive, widening primitive conversions are attempted, * else reference conversions are attempted. *

The returned method handle is equivalent to {@code identity(type).bindTo(value)}. * @param type the return type of the desired method handle * @param value the value to return * @return a method handle of the given return type and no arguments, which always returns the given value * @throws NullPointerException if the {@code type} argument is null * @throws ClassCastException if the value cannot be converted to the required return type * @throws IllegalArgumentException if the given type is {@code void.class} */ public static MethodHandle constant(Class type, Object value) { if (type.isPrimitive()) { if (type == void.class) throw newIllegalArgumentException("void type"); Wrapper w = Wrapper.forPrimitiveType(type); return insertArguments(identity(type), 0, w.convert(value, type)); } else { return identity(type).bindTo(type.cast(value)); } } /** * Produces a method handle which returns its sole argument when invoked. * @param type the type of the sole parameter and return value of the desired method handle * @return a unary method handle which accepts and returns the given type * @throws NullPointerException if the argument is null * @throws IllegalArgumentException if the given type is {@code void.class} */ public static MethodHandle identity(Class type) { if (type == void.class) throw newIllegalArgumentException("void type"); else if (type == Object.class) return ValueConversions.identity(); else if (type.isPrimitive()) return ValueConversions.identity(Wrapper.forPrimitiveType(type)); else return MethodHandleImpl.makeReferenceIdentity(type); } /** * Provides a target method handle with one or more bound arguments * in advance of the method handle's invocation. * The formal parameters to the target corresponding to the bound * arguments are called bound parameters. * Returns a new method handle which saves away the bound arguments. * When it is invoked, it receives arguments for any non-bound parameters, * binds the saved arguments to their corresponding parameters, * and calls the original target. *

* The type of the new method handle will drop the types for the bound * parameters from the original target type, since the new method handle * will no longer require those arguments to be supplied by its callers. *

* Each given argument object must match the corresponding bound parameter type. * If a bound parameter type is a primitive, the argument object * must be a wrapper, and will be unboxed to produce the primitive value. *

* The {@code pos} argument selects which parameters are to be bound. * It may range between zero and N-L (inclusively), * where N is the arity of the target method handle * and L is the length of the values array. * @param target the method handle to invoke after the argument is inserted * @param pos where to insert the argument (zero for the first) * @param values the series of arguments to insert * @return a method handle which inserts an additional argument, * before calling the original method handle * @throws NullPointerException if the target or the {@code values} array is null * @see MethodHandle#bindTo */ public static MethodHandle insertArguments(MethodHandle target, int pos, Object... values) { int insCount = values.length; MethodType oldType = target.type(); int outargs = oldType.parameterCount(); int inargs = outargs - insCount; if (inargs < 0) throw newIllegalArgumentException("too many values to insert"); if (pos < 0 || pos > inargs) throw newIllegalArgumentException("no argument type to append"); MethodHandle result = target; for (int i = 0; i < insCount; i++) { Object value = values[i]; Class ptype = oldType.parameterType(pos+i); if (ptype.isPrimitive()) { char btype = 'I'; Wrapper w = Wrapper.forPrimitiveType(ptype); switch (w) { case LONG: btype = 'J'; break; case FLOAT: btype = 'F'; break; case DOUBLE: btype = 'D'; break; } // perform unboxing and/or primitive conversion value = w.convert(value, ptype); result = result.bindArgument(pos, btype, value); continue; } value = ptype.cast(value); // throw CCE if needed if (pos == 0) { result = result.bindReceiver(value); } else { result = result.bindArgument(pos, 'L', value); } } return result; } /** * Produces a method handle which will discard some dummy arguments * before calling some other specified target method handle. * The type of the new method handle will be the same as the target's type, * except it will also include the dummy argument types, * at some given position. *

* The {@code pos} argument may range between zero and N, * where N is the arity of the target. * If {@code pos} is zero, the dummy arguments will precede * the target's real arguments; if {@code pos} is N * they will come after. *

* Example: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
assertEquals(bigType, d0.type());
assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
     * 
*

* This method is also equivalent to the following code: *

     * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
     * 
* @param target the method handle to invoke after the arguments are dropped * @param valueTypes the type(s) of the argument(s) to drop * @param pos position of first argument to drop (zero for the leftmost) * @return a method handle which drops arguments of the given types, * before calling the original method handle * @throws NullPointerException if the target is null, * or if the {@code valueTypes} list or any of its elements is null * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, * or if {@code pos} is negative or greater than the arity of the target, * or if the new method handle's type would have too many parameters */ public static MethodHandle dropArguments(MethodHandle target, int pos, List> valueTypes) { MethodType oldType = target.type(); // get NPE int dropped = valueTypes.size(); MethodType.checkSlotCount(dropped); if (dropped == 0) return target; int outargs = oldType.parameterCount(); int inargs = outargs + dropped; if (pos < 0 || pos >= inargs) throw newIllegalArgumentException("no argument type to remove"); ArrayList> ptypes = new ArrayList<>(oldType.parameterList()); ptypes.addAll(pos, valueTypes); MethodType newType = MethodType.methodType(oldType.returnType(), ptypes); return target.dropArguments(newType, pos, dropped); } /** * Produces a method handle which will discard some dummy arguments * before calling some other specified target method handle. * The type of the new method handle will be the same as the target's type, * except it will also include the dummy argument types, * at some given position. *

* The {@code pos} argument may range between zero and N, * where N is the arity of the target. * If {@code pos} is zero, the dummy arguments will precede * the target's real arguments; if {@code pos} is N * they will come after. *

* Example: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle d0 = dropArguments(cat, 0, String.class);
assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
MethodHandle d1 = dropArguments(cat, 1, String.class);
assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
MethodHandle d2 = dropArguments(cat, 2, String.class);
assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
     * 
*

* This method is also equivalent to the following code: *

     * {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
     * 
* @param target the method handle to invoke after the arguments are dropped * @param valueTypes the type(s) of the argument(s) to drop * @param pos position of first argument to drop (zero for the leftmost) * @return a method handle which drops arguments of the given types, * before calling the original method handle * @throws NullPointerException if the target is null, * or if the {@code valueTypes} array or any of its elements is null * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class}, * or if {@code pos} is negative or greater than the arity of the target, * or if the new method handle's type would have too many parameters */ public static MethodHandle dropArguments(MethodHandle target, int pos, Class... valueTypes) { return dropArguments(target, pos, Arrays.asList(valueTypes)); } /** * Adapts a target method handle by pre-processing * one or more of its arguments, each with its own unary filter function, * and then calling the target with each pre-processed argument * replaced by the result of its corresponding filter function. *

* The pre-processing is performed by one or more method handles, * specified in the elements of the {@code filters} array. * The first element of the filter array corresponds to the {@code pos} * argument of the target, and so on in sequence. *

* Null arguments in the array are treated as identity functions, * and the corresponding arguments left unchanged. * (If there are no non-null elements in the array, the original target is returned.) * Each filter is applied to the corresponding argument of the adapter. *

* If a filter {@code F} applies to the {@code N}th argument of * the target, then {@code F} must be a method handle which * takes exactly one argument. The type of {@code F}'s sole argument * replaces the corresponding argument type of the target * in the resulting adapted method handle. * The return type of {@code F} must be identical to the corresponding * parameter type of the target. *

* It is an error if there are elements of {@code filters} * (null or not) * which do not correspond to argument positions in the target. * Example: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
MethodHandle upcase = lookup().findVirtual(String.class,
  "toUpperCase", methodType(String.class));
assertEquals("xy", (String) cat.invokeExact("x", "y"));
MethodHandle f0 = filterArguments(cat, 0, upcase);
assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
MethodHandle f1 = filterArguments(cat, 1, upcase);
assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
     * 
*

Here is pseudocode for the resulting adapter: *

     * V target(P... p, A[i]... a[i], B... b);
     * A[i] filter[i](V[i]);
     * T adapter(P... p, V[i]... v[i], B... b) {
     *   return target(p..., f[i](v[i])..., b...);
     * }
     * 
* * @param target the method handle to invoke after arguments are filtered * @param pos the position of the first argument to filter * @param filters method handles to call initially on filtered arguments * @return method handle which incorporates the specified argument filtering logic * @throws NullPointerException if the target is null * or if the {@code filters} array is null * @throws IllegalArgumentException if a non-null element of {@code filters} * does not match a corresponding argument type of target as described above, * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()} */ public static MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) { MethodType targetType = target.type(); MethodHandle adapter = target; MethodType adapterType = null; assert((adapterType = targetType) != null); int maxPos = targetType.parameterCount(); if (pos + filters.length > maxPos) throw newIllegalArgumentException("too many filters"); int curPos = pos-1; // pre-incremented for (MethodHandle filter : filters) { curPos += 1; if (filter == null) continue; // ignore null elements of filters adapter = filterArgument(adapter, curPos, filter); assert((adapterType = adapterType.changeParameterType(curPos, filter.type().parameterType(0))) != null); } assert(adapterType.equals(adapter.type())); return adapter; } /*non-public*/ static MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) { MethodType targetType = target.type(); MethodType filterType = filter.type(); if (filterType.parameterCount() != 1 || filterType.returnType() != targetType.parameterType(pos)) throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); return MethodHandleImpl.makeCollectArguments(target, filter, pos, false); } // FIXME: Make this public in M1. /*non-public*/ static MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle collector) { MethodType targetType = target.type(); MethodType filterType = collector.type(); if (filterType.returnType() != void.class && filterType.returnType() != targetType.parameterType(pos)) throw newIllegalArgumentException("target and filter types do not match", targetType, filterType); return MethodHandleImpl.makeCollectArguments(target, collector, pos, false); } /** * Adapts a target method handle by post-processing * its return value (if any) with a filter (another method handle). * The result of the filter is returned from the adapter. *

* If the target returns a value, the filter must accept that value as * its only argument. * If the target returns void, the filter must accept no arguments. *

* The return type of the filter * replaces the return type of the target * in the resulting adapted method handle. * The argument type of the filter (if any) must be identical to the * return type of the target. * Example: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
MethodHandle length = lookup().findVirtual(String.class,
  "length", methodType(int.class));
System.out.println((String) cat.invokeExact("x", "y")); // xy
MethodHandle f0 = filterReturnValue(cat, length);
System.out.println((int) f0.invokeExact("x", "y")); // 2
     * 
*

Here is pseudocode for the resulting adapter: *

     * V target(A...);
     * T filter(V);
     * T adapter(A... a) {
     *   V v = target(a...);
     *   return filter(v);
     * }
     * // and if the target has a void return:
     * void target2(A...);
     * T filter2();
     * T adapter2(A... a) {
     *   target2(a...);
     *   return filter2();
     * }
     * // and if the filter has a void return:
     * V target3(A...);
     * void filter3(V);
     * void adapter3(A... a) {
     *   V v = target3(a...);
     *   filter3(v);
     * }
     * 
* @param target the method handle to invoke before filtering the return value * @param filter method handle to call on the return value * @return method handle which incorporates the specified return value filtering logic * @throws NullPointerException if either argument is null * @throws IllegalArgumentException if the argument list of {@code filter} * does not match the return type of target as described above */ public static MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) { MethodType targetType = target.type(); MethodType filterType = filter.type(); Class rtype = targetType.returnType(); int filterValues = filterType.parameterCount(); if (filterValues == 0 ? (rtype != void.class) : (rtype != filterType.parameterType(0))) throw newIllegalArgumentException("target and filter types do not match", target, filter); // result = fold( lambda(retval, arg...) { filter(retval) }, // lambda( arg...) { target(arg...) } ) return MethodHandleImpl.makeCollectArguments(filter, target, 0, false); } /** * Adapts a target method handle by pre-processing * some of its arguments, and then calling the target with * the result of the pre-processing, inserted into the original * sequence of arguments. *

* The pre-processing is performed by {@code combiner}, a second method handle. * Of the arguments passed to the adapter, the first {@code N} arguments * are copied to the combiner, which is then called. * (Here, {@code N} is defined as the parameter count of the combiner.) * After this, control passes to the target, with any result * from the combiner inserted before the original {@code N} incoming * arguments. *

* If the combiner returns a value, the first parameter type of the target * must be identical with the return type of the combiner, and the next * {@code N} parameter types of the target must exactly match the parameters * of the combiner. *

* If the combiner has a void return, no result will be inserted, * and the first {@code N} parameter types of the target * must exactly match the parameters of the combiner. *

* The resulting adapter is the same type as the target, except that the * first parameter type is dropped, * if it corresponds to the result of the combiner. *

* (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments * that either the combiner or the target does not wish to receive. * If some of the incoming arguments are destined only for the combiner, * consider using {@link MethodHandle#asCollector asCollector} instead, since those * arguments will not need to be live on the stack on entry to the * target.) * Example: *

import static java.lang.invoke.MethodHandles.*;
import static java.lang.invoke.MethodType.*;
...
MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
  "println", methodType(void.class, String.class))
    .bindTo(System.out);
MethodHandle cat = lookup().findVirtual(String.class,
  "concat", methodType(String.class, String.class));
assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
MethodHandle catTrace = foldArguments(cat, trace);
// also prints "boo":
assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
     * 
*

Here is pseudocode for the resulting adapter: *

     * // there are N arguments in A...
     * T target(V, A[N]..., B...);
     * V combiner(A...);
     * T adapter(A... a, B... b) {
     *   V v = combiner(a...);
     *   return target(v, a..., b...);
     * }
     * // and if the combiner has a void return:
     * T target2(A[N]..., B...);
     * void combiner2(A...);
     * T adapter2(A... a, B... b) {
     *   combiner2(a...);
     *   return target2(a..., b...);
     * }
     * 
* @param target the method handle to invoke after arguments are combined * @param combiner method handle to call initially on the incoming arguments * @return method handle which incorporates the specified argument folding logic * @throws NullPointerException if either argument is null * @throws IllegalArgumentException if {@code combiner}'s return type * is non-void and not the same as the first argument type of * the target, or if the initial {@code N} argument types * of the target * (skipping one matching the {@code combiner}'s return type) * are not identical with the argument types of {@code combiner} */ public static MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) { int pos = 0; MethodType targetType = target.type(); MethodType combinerType = combiner.type(); int foldPos = pos; int foldArgs = combinerType.parameterCount(); int foldVals = combinerType.returnType() == void.class ? 0 : 1; int afterInsertPos = foldPos + foldVals; boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs); if (ok && !(combinerType.parameterList() .equals(targetType.parameterList().subList(afterInsertPos, afterInsertPos + foldArgs)))) ok = false; if (ok && foldVals != 0 && !combinerType.returnType().equals(targetType.parameterType(0))) ok = false; if (!ok) throw misMatchedTypes("target and combiner types", targetType, combinerType); MethodType newType = targetType.dropParameterTypes(foldPos, afterInsertPos); return MethodHandleImpl.makeCollectArguments(target, combiner, foldPos, true); } /** * Makes a method handle which adapts a target method handle, * by guarding it with a test, a boolean-valued method handle. * If the guard fails, a fallback handle is called instead. * All three method handles must have the same corresponding * argument and return types, except that the return type * of the test must be boolean, and the test is allowed * to have fewer arguments than the other two method handles. *

Here is pseudocode for the resulting adapter: *

     * boolean test(A...);
     * T target(A...,B...);
     * T fallback(A...,B...);
     * T adapter(A... a,B... b) {
     *   if (test(a...))
     *     return target(a..., b...);
     *   else
     *     return fallback(a..., b...);
     * }
     * 
* Note that the test arguments ({@code a...} in the pseudocode) cannot * be modified by execution of the test, and so are passed unchanged * from the caller to the target or fallback as appropriate. * @param test method handle used for test, must return boolean * @param target method handle to call if test passes * @param fallback method handle to call if test fails * @return method handle which incorporates the specified if/then/else logic * @throws NullPointerException if any argument is null * @throws IllegalArgumentException if {@code test} does not return boolean, * or if all three method types do not match (with the return * type of {@code test} changed to match that of the target). */ public static MethodHandle guardWithTest(MethodHandle test, MethodHandle target, MethodHandle fallback) { MethodType gtype = test.type(); MethodType ttype = target.type(); MethodType ftype = fallback.type(); if (!ttype.equals(ftype)) throw misMatchedTypes("target and fallback types", ttype, ftype); if (gtype.returnType() != boolean.class) throw newIllegalArgumentException("guard type is not a predicate "+gtype); List> targs = ttype.parameterList(); List> gargs = gtype.parameterList(); if (!targs.equals(gargs)) { int gpc = gargs.size(), tpc = targs.size(); if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs)) throw misMatchedTypes("target and test types", ttype, gtype); test = dropArguments(test, gpc, targs.subList(gpc, tpc)); gtype = test.type(); } return MethodHandleImpl.makeGuardWithTest(test, target, fallback); } static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) { return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2); } /** * Makes a method handle which adapts a target method handle, * by running it inside an exception handler. * If the target returns normally, the adapter returns that value. * If an exception matching the specified type is thrown, the fallback * handle is called instead on the exception, plus the original arguments. *

* The target and handler must have the same corresponding * argument and return types, except that handler may omit trailing arguments * (similarly to the predicate in {@link #guardWithTest guardWithTest}). * Also, the handler must have an extra leading parameter of {@code exType} or a supertype. *

Here is pseudocode for the resulting adapter: *

     * T target(A..., B...);
     * T handler(ExType, A...);
     * T adapter(A... a, B... b) {
     *   try {
     *     return target(a..., b...);
     *   } catch (ExType ex) {
     *     return handler(ex, a...);
     *   }
     * }
     * 
* Note that the saved arguments ({@code a...} in the pseudocode) cannot * be modified by execution of the target, and so are passed unchanged * from the caller to the handler, if the handler is invoked. *

* The target and handler must return the same type, even if the handler * always throws. (This might happen, for instance, because the handler * is simulating a {@code finally} clause). * To create such a throwing handler, compose the handler creation logic * with {@link #throwException throwException}, * in order to create a method handle of the correct return type. * @param target method handle to call * @param exType the type of exception which the handler will catch * @param handler method handle to call if a matching exception is thrown * @return method handle which incorporates the specified try/catch logic * @throws NullPointerException if any argument is null * @throws IllegalArgumentException if {@code handler} does not accept * the given exception type, or if the method handle types do * not match in their return types and their * corresponding parameters */ public static MethodHandle catchException(MethodHandle target, Class exType, MethodHandle handler) { MethodType ttype = target.type(); MethodType htype = handler.type(); if (htype.parameterCount() < 1 || !htype.parameterType(0).isAssignableFrom(exType)) throw newIllegalArgumentException("handler does not accept exception type "+exType); if (htype.returnType() != ttype.returnType()) throw misMatchedTypes("target and handler return types", ttype, htype); List> targs = ttype.parameterList(); List> hargs = htype.parameterList(); hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler if (!targs.equals(hargs)) { int hpc = hargs.size(), tpc = targs.size(); if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs)) throw misMatchedTypes("target and handler types", ttype, htype); handler = dropArguments(handler, 1+hpc, targs.subList(hpc, tpc)); htype = handler.type(); } return MethodHandleImpl.makeGuardWithCatch(target, exType, handler); } /** * Produces a method handle which will throw exceptions of the given {@code exType}. * The method handle will accept a single argument of {@code exType}, * and immediately throw it as an exception. * The method type will nominally specify a return of {@code returnType}. * The return type may be anything convenient: It doesn't matter to the * method handle's behavior, since it will never return normally. * @return method handle which can throw the given exceptions * @throws NullPointerException if either argument is null */ public static MethodHandle throwException(Class returnType, Class exType) { if (!Throwable.class.isAssignableFrom(exType)) throw new ClassCastException(exType.getName()); return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType)); } }