| /* |
| * 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 Ahé |
| */ |
| 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); |
| } |
| } |
| } |