/*

 * 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);

        }

    }

}