Wed, 24 Sep 2014 11:38:26 -0700
Added tag jdk8u40-b07 for changeset 2fa3858a281f
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 */
24 package evalexpr;
26 import java.lang.reflect.Method;
27 import java.util.*;
28 import javax.swing.JOptionPane;
29 import javax.tools.*;
30 import static javax.tools.StandardLocation.CLASS_OUTPUT;
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 */
42 public class CompileFromString {
44 /**
45 * The name of the class used to evaluate expressions.
46 */
47 private final static String CLASS_NAME = "EvalExpression";
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 };
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));
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");
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 }
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 }