/*
* Copyright (c) 2005, 2006, 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.
*
* 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 evalexpr;
import java.lang.reflect.Method;
import java.util.*;
import javax.swing.JOptionPane;
import javax.tools.*;
import static javax.tools.StandardLocation.CLASS_OUTPUT;
/**
* JSR 199 Demo application: compile from a String.
*
* <p><b>This is NOT part of any supported API.
* If you write code that depends on this, you do so at your own
* risk. This code and its internal interfaces are subject to change
* or deletion without notice.</b></p>
*
* @author Peter von der Ah&eacute;
*/
public class CompileFromString {
/**
* The name of the class used to evaluate expressions.
*/
private final static String CLASS_NAME = "EvalExpression";
/**
* Object used to signal errors from evalExpression.
*/
public final static Object ERROR = new Object() {
public String toString() { return "error"; }
};
/**
* Compile and evaluate the specified expression using the
* given compiler.
* @param compiler a JSR 199 compiler tool used to compile the given expression
* @param expression a Java Programming Language expression
* @return the value of the expression; ERROR if any errors occured during compilation
* @throws java.lang.Exception exceptions are ignored for brevity
*/
public static Object evalExpression(JavaCompiler compiler,
DiagnosticListener<JavaFileObject> listener,
List<String> flags,
String expression)
throws Exception
{
// Use a customized file manager
MemoryFileManager mfm =
new MemoryFileManager(compiler.getStandardFileManager(listener, null, null));
// Create a file object from a string
JavaFileObject fileObject = mfm.makeSource(CLASS_NAME,
"public class " + CLASS_NAME + " {\n" +
" public static Object eval() throws Throwable {\n" +
" return " + expression + ";\n" +
" }\n}\n");
JavaCompiler.CompilationTask task =
compiler.getTask(null, mfm, listener, flags, null, Arrays.asList(fileObject));
if (task.call()) {
// Obtain a class loader for the compiled classes
ClassLoader cl = mfm.getClassLoader(CLASS_OUTPUT);
// Load the compiled class
Class compiledClass = cl.loadClass(CLASS_NAME);
// Find the eval method
Method eval = compiledClass.getMethod("eval");
// Invoke it
return eval.invoke(null);
} else {
// Report that an error occured
return ERROR;
}
}
/**
* Main entry point for program; ask user for expressions,
* compile, evaluate, and print them.
*
* @param args ignored
* @throws java.lang.Exception exceptions are ignored for brevity
*/
public static void main(String... args) throws Exception {
// Get a compiler tool
final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
final List<String> compilerFlags = new ArrayList();
compilerFlags.add("-Xlint:all"); // report all warnings
compilerFlags.add("-g:none"); // don't generate debug info
String expression = "System.getProperty(\"java.vendor\")";
while (true) {
expression = JOptionPane.showInputDialog("Please enter a Java expression",
expression);
if (expression == null)
return; // end program on "cancel"
long time = System.currentTimeMillis();
Object result = evalExpression(compiler, null, compilerFlags, expression);
time = System.currentTimeMillis() - time;
System.out.format("Elapsed time %dms %n", time);
if (result == ERROR)
System.out.format("Error compiling \"%s\"%n", expression);
else
System.out.format("%s => %s%n", expression, result);
}
}
}