duke@1: /*
ohair@554:  * Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved.
duke@1:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@1:  *
duke@1:  * This code is free software; you can redistribute it and/or modify it
duke@1:  * under the terms of the GNU General Public License version 2 only, as
duke@1:  * published by the Free Software Foundation.
duke@1:  *
duke@1:  * This code is distributed in the hope that it will be useful, but WITHOUT
duke@1:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@1:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
duke@1:  * version 2 for more details (a copy is included in the LICENSE file that
duke@1:  * accompanied this code).
duke@1:  *
duke@1:  * You should have received a copy of the GNU General Public License version
duke@1:  * 2 along with this work; if not, write to the Free Software Foundation,
duke@1:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@1:  *
ohair@554:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
ohair@554:  * or visit www.oracle.com if you need additional information or have any
ohair@554:  * questions.
duke@1:  */
duke@1: 
duke@1: package evalexpr;
duke@1: 
duke@1: import java.lang.reflect.Method;
duke@1: import java.util.*;
duke@1: import javax.swing.JOptionPane;
duke@1: import javax.tools.*;
duke@1: import static javax.tools.StandardLocation.CLASS_OUTPUT;
duke@1: 
duke@1: /**
duke@1:  * JSR 199 Demo application: compile from a String.
duke@1:  *
jjg@581:  * <p><b>This is NOT part of any supported API.
duke@1:  * If you write code that depends on this, you do so at your own
duke@1:  * risk.  This code and its internal interfaces are subject to change
duke@1:  * or deletion without notice.</b></p>
duke@1:  *
duke@1:  * @author Peter von der Ah&eacute;
duke@1:  */
duke@1: public class CompileFromString {
duke@1: 
duke@1:     /**
duke@1:      * The name of the class used to evaluate expressions.
duke@1:      */
duke@1:     private final static String CLASS_NAME = "EvalExpression";
duke@1: 
duke@1:     /**
duke@1:      * Object used to signal errors from evalExpression.
duke@1:      */
duke@1:     public final static Object ERROR = new Object() {
duke@1:         public String toString() { return "error"; }
duke@1:     };
duke@1: 
duke@1:     /**
duke@1:      * Compile and evaluate the specified expression using the
duke@1:      * given compiler.
duke@1:      * @param compiler a JSR 199 compiler tool used to compile the given expression
duke@1:      * @param expression a Java Programming Language expression
duke@1:      * @return the value of the expression; ERROR if any errors occured during compilation
duke@1:      * @throws java.lang.Exception exceptions are ignored for brevity
duke@1:      */
duke@1:     public static Object evalExpression(JavaCompiler compiler,
duke@1:                                         DiagnosticListener<JavaFileObject> listener,
duke@1:                                         List<String> flags,
duke@1:                                         String expression)
duke@1:         throws Exception
duke@1:     {
duke@1:         // Use a customized file manager
duke@1:         MemoryFileManager mfm =
duke@1:             new MemoryFileManager(compiler.getStandardFileManager(listener, null, null));
duke@1: 
duke@1:         // Create a file object from a string
duke@1:         JavaFileObject fileObject = mfm.makeSource(CLASS_NAME,
duke@1:             "public class " + CLASS_NAME + " {\n" +
duke@1:             "    public static Object eval() throws Throwable {\n" +
duke@1:             "        return " + expression + ";\n" +
duke@1:             "    }\n}\n");
duke@1: 
duke@1:         JavaCompiler.CompilationTask task =
duke@1:             compiler.getTask(null, mfm, listener, flags, null, Arrays.asList(fileObject));
duke@1:         if (task.call()) {
duke@1:             // Obtain a class loader for the compiled classes
duke@1:             ClassLoader cl = mfm.getClassLoader(CLASS_OUTPUT);
duke@1:             // Load the compiled class
duke@1:             Class compiledClass = cl.loadClass(CLASS_NAME);
duke@1:             // Find the eval method
duke@1:             Method eval = compiledClass.getMethod("eval");
duke@1:             // Invoke it
duke@1:             return eval.invoke(null);
duke@1:         } else {
duke@1:             // Report that an error occured
duke@1:             return ERROR;
duke@1:         }
duke@1:     }
duke@1: 
duke@1:     /**
duke@1:      * Main entry point for program; ask user for expressions,
duke@1:      * compile, evaluate, and print them.
duke@1:      *
duke@1:      * @param args ignored
duke@1:      * @throws java.lang.Exception exceptions are ignored for brevity
duke@1:      */
duke@1:     public static void main(String... args) throws Exception {
duke@1:         // Get a compiler tool
duke@1:         final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
duke@1:         final List<String> compilerFlags = new ArrayList();
duke@1:         compilerFlags.add("-Xlint:all"); // report all warnings
duke@1:         compilerFlags.add("-g:none"); // don't generate debug info
duke@1:         String expression = "System.getProperty(\"java.vendor\")";
duke@1:         while (true) {
duke@1:             expression = JOptionPane.showInputDialog("Please enter a Java expression",
duke@1:                                                      expression);
duke@1:             if (expression == null)
duke@1:                 return; // end program on "cancel"
duke@1:             long time = System.currentTimeMillis();
duke@1:             Object result = evalExpression(compiler, null, compilerFlags, expression);
duke@1:             time = System.currentTimeMillis() - time;
duke@1:             System.out.format("Elapsed time %dms %n", time);
duke@1:             if (result == ERROR)
duke@1:                 System.out.format("Error compiling \"%s\"%n", expression);
duke@1:             else
duke@1:                 System.out.format("%s => %s%n", expression, result);
duke@1:         }
duke@1:     }
duke@1: }