1/* 2 * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24package evalexpr; 25 26import java.lang.reflect.Method; 27import java.util.*; 28import javax.swing.JOptionPane; 29import javax.tools.*; 30import static javax.tools.StandardLocation.CLASS_OUTPUT; 31 32/** 33 * JSR 199 Demo application: compile from a String. 34 * 35 * <p><b>This is NOT part of any supported API. 36 * If you write code that depends on this, you do so at your own 37 * risk. This code and its internal interfaces are subject to change 38 * or deletion without notice.</b></p> 39 * 40 * @author Peter von der Ahé 41 */ 42public class CompileFromString { 43 44 /** 45 * The name of the class used to evaluate expressions. 46 */ 47 private final static String CLASS_NAME = "EvalExpression"; 48 49 /** 50 * Object used to signal errors from evalExpression. 51 */ 52 public final static Object ERROR = new Object() { 53 public String toString() { return "error"; } 54 }; 55 56 /** 57 * Compile and evaluate the specified expression using the 58 * given compiler. 59 * @param compiler a JSR 199 compiler tool used to compile the given expression 60 * @param expression a Java Programming Language expression 61 * @return the value of the expression; ERROR if any errors occured during compilation 62 * @throws java.lang.Exception exceptions are ignored for brevity 63 */ 64 public static Object evalExpression(JavaCompiler compiler, 65 DiagnosticListener<JavaFileObject> listener, 66 List<String> flags, 67 String expression) 68 throws Exception 69 { 70 // Use a customized file manager 71 MemoryFileManager mfm = 72 new MemoryFileManager(compiler.getStandardFileManager(listener, null, null)); 73 74 // Create a file object from a string 75 JavaFileObject fileObject = mfm.makeSource(CLASS_NAME, 76 "public class " + CLASS_NAME + " {\n" + 77 " public static Object eval() throws Throwable {\n" + 78 " return " + expression + ";\n" + 79 " }\n}\n"); 80 81 JavaCompiler.CompilationTask task = 82 compiler.getTask(null, mfm, listener, flags, null, Arrays.asList(fileObject)); 83 if (task.call()) { 84 // Obtain a class loader for the compiled classes 85 ClassLoader cl = mfm.getClassLoader(CLASS_OUTPUT); 86 // Load the compiled class 87 Class compiledClass = cl.loadClass(CLASS_NAME); 88 // Find the eval method 89 Method eval = compiledClass.getMethod("eval"); 90 // Invoke it 91 return eval.invoke(null); 92 } else { 93 // Report that an error occured 94 return ERROR; 95 } 96 } 97 98 /** 99 * Main entry point for program; ask user for expressions, 100 * compile, evaluate, and print them. 101 * 102 * @param args ignored 103 * @throws java.lang.Exception exceptions are ignored for brevity 104 */ 105 public static void main(String... args) throws Exception { 106 // Get a compiler tool 107 final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); 108 final List<String> compilerFlags = new ArrayList(); 109 compilerFlags.add("-Xlint:all"); // report all warnings 110 compilerFlags.add("-g:none"); // don't generate debug info 111 String expression = "System.getProperty(\"java.vendor\")"; 112 while (true) { 113 expression = JOptionPane.showInputDialog("Please enter a Java expression", 114 expression); 115 if (expression == null) 116 return; // end program on "cancel" 117 long time = System.currentTimeMillis(); 118 Object result = evalExpression(compiler, null, compilerFlags, expression); 119 time = System.currentTimeMillis() - time; 120 System.out.format("Elapsed time %dms %n", time); 121 if (result == ERROR) 122 System.out.format("Error compiling \"%s\"%n", expression); 123 else 124 System.out.format("%s => %s%n", expression, result); 125 } 126 } 127} 128