/* * Copyright (c) 2000, 2010, 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.beans; import com.sun.beans.finder.PersistenceDelegateFinder; import java.util.HashMap; import java.util.IdentityHashMap; import java.util.Map; /** * An Encoder is a class which can be used to create * files or streams that encode the state of a collection of * JavaBeans in terms of their public APIs. The Encoder, * in conjunction with its persistence delegates, is responsible for * breaking the object graph down into a series of Statementss * and Expressions which can be used to create it. * A subclass typically provides a syntax for these expressions * using some human readable form - like Java source code or XML. * * @since 1.4 * * @author Philip Milne */ public class Encoder { private final PersistenceDelegateFinder finder = new PersistenceDelegateFinder(); private Map bindings = new IdentityHashMap(); private ExceptionListener exceptionListener; boolean executeStatements = true; private Map attributes; /** * Write the specified object to the output stream. * The serialized form will denote a series of * expressions, the combined effect of which will create * an equivalent object when the input stream is read. * By default, the object is assumed to be a JavaBean * with a nullary constructor, whose state is defined by * the matching pairs of "setter" and "getter" methods * returned by the Introspector. * * @param o The object to be written to the stream. * * @see XMLDecoder#readObject */ protected void writeObject(Object o) { if (o == this) { return; } PersistenceDelegate info = getPersistenceDelegate(o == null ? null : o.getClass()); info.writeObject(o, this); } /** * Sets the exception handler for this stream to exceptionListener. * The exception handler is notified when this stream catches recoverable * exceptions. * * @param exceptionListener The exception handler for this stream; * if null the default exception listener will be used. * * @see #getExceptionListener */ public void setExceptionListener(ExceptionListener exceptionListener) { this.exceptionListener = exceptionListener; } /** * Gets the exception handler for this stream. * * @return The exception handler for this stream; * Will return the default exception listener if this has not explicitly been set. * * @see #setExceptionListener */ public ExceptionListener getExceptionListener() { return (exceptionListener != null) ? exceptionListener : Statement.defaultExceptionListener; } Object getValue(Expression exp) { try { return (exp == null) ? null : exp.getValue(); } catch (Exception e) { getExceptionListener().exceptionThrown(e); throw new RuntimeException("failed to evaluate: " + exp.toString()); } } /** * Returns the persistence delegate for the given type. * The persistence delegate is calculated by applying * the following rules in order: *
    *
  1. * If a persistence delegate is associated with the given type * by using the {@link #setPersistenceDelegate} method * it is returned. *
  2. * A persistence delegate is then looked up by the name * composed of the the fully qualified name of the given type * and the "PersistenceDelegate" postfix. * For example, a persistence delegate for the {@code Bean} class * should be named {@code BeanPersistenceDelegate} * and located in the same package. *
         * public class Bean { ... }
         * public class BeanPersistenceDelegate { ... }
    * The instance of the {@code BeanPersistenceDelegate} class * is returned for the {@code Bean} class. *
  3. * If the type is {@code null}, * a shared internal persistence delegate is returned * that encodes {@code null} value. *
  4. * If the type is a {@code enum} declaration, * a shared internal persistence delegate is returned * that encodes constants of this enumeration * by their names. *
  5. * If the type is a primitive type or the corresponding wrapper, * a shared internal persistence delegate is returned * that encodes values of the given type. *
  6. * If the type is an array, * a shared internal persistence delegate is returned * that encodes an array of the appropriate type and length, * and each of its elements as if they are properties. *
  7. * If the type is a proxy, * a shared internal persistence delegate is returned * that encodes a proxy instance by using * the {@link java.lang.reflect.Proxy#newProxyInstance} method. *
  8. * If the {@link BeanInfo} for this type has a {@link BeanDescriptor} * which defined a "persistenceDelegate" attribute, * the value of this named attribute is returned. *
  9. * In all other cases the default persistence delegate is returned. * The default persistence delegate assumes the type is a JavaBean, * implying that it has a default constructor and that its state * may be characterized by the matching pairs of "setter" and "getter" * methods returned by the {@link Introspector} class. * The default constructor is the constructor with the greatest number * of parameters that has the {@link ConstructorProperties} annotation. * If none of the constructors has the {@code ConstructorProperties} annotation, * then the nullary constructor (constructor with no parameters) will be used. * For example, in the following code fragment, the nullary constructor * for the {@code Foo} class will be used, * while the two-parameter constructor * for the {@code Bar} class will be used. *
         * public class Foo {
         *     public Foo() { ... }
         *     public Foo(int x) { ... }
         * }
         * public class Bar {
         *     public Bar() { ... }
         *     @ConstructorProperties({"x"})
         *     public Bar(int x) { ... }
         *     @ConstructorProperties({"x", "y"})
         *     public Bar(int x, int y) { ... }
         * }
    *
* * @param type the class of the objects * @return the persistence delegate for the given type * * @see #setPersistenceDelegate * @see java.beans.Introspector#getBeanInfo * @see java.beans.BeanInfo#getBeanDescriptor */ public PersistenceDelegate getPersistenceDelegate(Class type) { PersistenceDelegate pd = this.finder.find(type); if (pd == null) { pd = MetaData.getPersistenceDelegate(type); if (pd != null) { this.finder.register(type, pd); } } return pd; } /** * Associates the specified persistence delegate with the given type. * * @param type the class of objects that the specified persistence delegate applies to * @param delegate the persistence delegate for instances of the given type * * @see #getPersistenceDelegate * @see java.beans.Introspector#getBeanInfo * @see java.beans.BeanInfo#getBeanDescriptor */ public void setPersistenceDelegate(Class type, PersistenceDelegate delegate) { this.finder.register(type, delegate); } /** * Removes the entry for this instance, returning the old entry. * * @param oldInstance The entry that should be removed. * @return The entry that was removed. * * @see #get */ public Object remove(Object oldInstance) { Expression exp = (Expression)bindings.remove(oldInstance); return getValue(exp); } /** * Returns a tentative value for oldInstance in * the environment created by this stream. A persistence * delegate can use its mutatesTo method to * determine whether this value may be initialized to * form the equivalent object at the output or whether * a new object must be instantiated afresh. If the * stream has not yet seen this value, null is returned. * * @param oldInstance The instance to be looked up. * @return The object, null if the object has not been seen before. */ public Object get(Object oldInstance) { if (oldInstance == null || oldInstance == this || oldInstance.getClass() == String.class) { return oldInstance; } Expression exp = (Expression)bindings.get(oldInstance); return getValue(exp); } private Object writeObject1(Object oldInstance) { Object o = get(oldInstance); if (o == null) { writeObject(oldInstance); o = get(oldInstance); } return o; } private Statement cloneStatement(Statement oldExp) { Object oldTarget = oldExp.getTarget(); Object newTarget = writeObject1(oldTarget); Object[] oldArgs = oldExp.getArguments(); Object[] newArgs = new Object[oldArgs.length]; for (int i = 0; i < oldArgs.length; i++) { newArgs[i] = writeObject1(oldArgs[i]); } Statement newExp = Statement.class.equals(oldExp.getClass()) ? new Statement(newTarget, oldExp.getMethodName(), newArgs) : new Expression(newTarget, oldExp.getMethodName(), newArgs); newExp.loader = oldExp.loader; return newExp; } /** * Writes statement oldStm to the stream. * The oldStm should be written entirely * in terms of the callers environment, i.e. the * target and all arguments should be part of the * object graph being written. These expressions * represent a series of "what happened" expressions * which tell the output stream how to produce an * object graph like the original. *

* The implementation of this method will produce * a second expression to represent the same expression in * an environment that will exist when the stream is read. * This is achieved simply by calling writeObject * on the target and all the arguments and building a new * expression with the results. * * @param oldStm The expression to be written to the stream. */ public void writeStatement(Statement oldStm) { // System.out.println("writeStatement: " + oldExp); Statement newStm = cloneStatement(oldStm); if (oldStm.getTarget() != this && executeStatements) { try { newStm.execute(); } catch (Exception e) { getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement " + newStm, e)); } } } /** * The implementation first checks to see if an * expression with this value has already been written. * If not, the expression is cloned, using * the same procedure as writeStatement, * and the value of this expression is reconciled * with the value of the cloned expression * by calling writeObject. * * @param oldExp The expression to be written to the stream. */ public void writeExpression(Expression oldExp) { // System.out.println("Encoder::writeExpression: " + oldExp); Object oldValue = getValue(oldExp); if (get(oldValue) != null) { return; } bindings.put(oldValue, (Expression)cloneStatement(oldExp)); writeObject(oldValue); } void clear() { bindings.clear(); } // Package private method for setting an attributes table for the encoder void setAttribute(Object key, Object value) { if (attributes == null) { attributes = new HashMap(); } attributes.put(key, value); } Object getAttribute(Object key) { if (attributes == null) { return null; } return attributes.get(key); } }