Mercurial > jdk8-mips64-public > langtools / file revision

 /*

  * 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);

         }

     }

 }