128 lines
5.0 KiB
Java
128 lines
5.0 KiB
Java
/*
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* Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package evalexpr;
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import java.lang.reflect.Method;
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import java.util.*;
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import javax.swing.JOptionPane;
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import javax.tools.*;
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import static javax.tools.StandardLocation.CLASS_OUTPUT;
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/**
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* JSR 199 Demo application: compile from a String.
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*
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* <p><b>This is NOT part of any supported API.
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* If you write code that depends on this, you do so at your own
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* risk. This code and its internal interfaces are subject to change
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* or deletion without notice.</b></p>
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*
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* @author Peter von der Ahé
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*/
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public class CompileFromString {
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/**
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* The name of the class used to evaluate expressions.
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*/
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private final static String CLASS_NAME = "EvalExpression";
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/**
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* Object used to signal errors from evalExpression.
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*/
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public final static Object ERROR = new Object() {
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public String toString() { return "error"; }
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};
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/**
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* Compile and evaluate the specified expression using the
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* given compiler.
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* @param compiler a JSR 199 compiler tool used to compile the given expression
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* @param expression a Java Programming Language expression
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* @return the value of the expression; ERROR if any errors occured during compilation
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* @throws java.lang.Exception exceptions are ignored for brevity
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*/
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public static Object evalExpression(JavaCompiler compiler,
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DiagnosticListener<JavaFileObject> listener,
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List<String> flags,
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String expression)
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throws Exception
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{
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// Use a customized file manager
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MemoryFileManager mfm =
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new MemoryFileManager(compiler.getStandardFileManager(listener, null, null));
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// Create a file object from a string
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JavaFileObject fileObject = mfm.makeSource(CLASS_NAME,
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"public class " + CLASS_NAME + " {\n" +
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" public static Object eval() throws Throwable {\n" +
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" return " + expression + ";\n" +
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" }\n}\n");
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JavaCompiler.CompilationTask task =
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compiler.getTask(null, mfm, listener, flags, null, Arrays.asList(fileObject));
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if (task.call()) {
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// Obtain a class loader for the compiled classes
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ClassLoader cl = mfm.getClassLoader(CLASS_OUTPUT);
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// Load the compiled class
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Class compiledClass = cl.loadClass(CLASS_NAME);
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// Find the eval method
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Method eval = compiledClass.getMethod("eval");
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// Invoke it
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return eval.invoke(null);
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} else {
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// Report that an error occured
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return ERROR;
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}
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}
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/**
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* Main entry point for program; ask user for expressions,
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* compile, evaluate, and print them.
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*
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* @param args ignored
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* @throws java.lang.Exception exceptions are ignored for brevity
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*/
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public static void main(String... args) throws Exception {
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// Get a compiler tool
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final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
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final List<String> compilerFlags = new ArrayList();
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compilerFlags.add("-Xlint:all"); // report all warnings
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compilerFlags.add("-g:none"); // don't generate debug info
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String expression = "System.getProperty(\"java.vendor\")";
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while (true) {
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expression = JOptionPane.showInputDialog("Please enter a Java expression",
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expression);
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if (expression == null)
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return; // end program on "cancel"
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long time = System.currentTimeMillis();
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Object result = evalExpression(compiler, null, compilerFlags, expression);
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time = System.currentTimeMillis() - time;
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System.out.format("Elapsed time %dms %n", time);
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if (result == ERROR)
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System.out.format("Error compiling \"%s\"%n", expression);
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else
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System.out.format("%s => %s%n", expression, result);
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}
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}
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}
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