001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 *  Unless required by applicable law or agreed to in writing, software
012 *  distributed under the License is distributed on an "AS IS" BASIS,
013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 *  See the License for the specific language governing permissions and
015 *  limitations under the License.
016 *
017 */
018package org.apache.bcel.util;
019
020import java.lang.reflect.Method;
021import java.lang.reflect.Modifier;
022
023/**
024 * Java interpreter replacement, i.e., wrapper that uses its own ClassLoader
025 * to modify/generate classes as they're requested. You can take this as a template
026 * for your own applications.
027 * <p>
028 * Call this wrapper with:
029 * </p>
030 * <pre>java org.apache.bcel.util.JavaWrapper &lt;real.class.name&gt; [arguments]</pre>
031 * <p>
032 * To use your own class loader you can set the "bcel.classloader" system property.
033 * </p>
034 * <pre>java org.apache.bcel.util.JavaWrapper -Dbcel.classloader=foo.MyLoader &lt;real.class.name&gt; [arguments]</pre>
035 *
036 * @see ClassLoader
037 */
038public class JavaWrapper {
039
040    private final java.lang.ClassLoader loader;
041
042
043    private static java.lang.ClassLoader getClassLoader() {
044        final String s = System.getProperty("bcel.classloader");
045        if ((s == null) || "".equals(s)) {
046            throw new IllegalArgumentException("The property 'bcel.classloader' must be defined");
047        }
048        try {
049            return (java.lang.ClassLoader) Class.forName(s).newInstance();
050        } catch (final Exception e) {
051            throw new RuntimeException(e.toString(), e);
052        }
053    }
054
055
056    public JavaWrapper(final java.lang.ClassLoader loader) {
057        this.loader = loader;
058    }
059
060
061    public JavaWrapper() {
062        this(getClassLoader());
063    }
064
065
066    /** Runs the main method of the given class with the arguments passed in argv
067     *
068     * @param class_name the fully qualified class name
069     * @param argv the arguments just as you would pass them directly
070     */
071    public void runMain( final String class_name, final String[] argv ) throws ClassNotFoundException {
072        final Class<?> cl = loader.loadClass(class_name);
073        Method method = null;
074        try {
075            method = cl.getMethod("main", new Class[] {
076                argv.getClass()
077            });
078            /* Method main is sane ?
079             */
080            final int m = method.getModifiers();
081            final Class<?> r = method.getReturnType();
082            if (!(Modifier.isPublic(m) && Modifier.isStatic(m)) || Modifier.isAbstract(m)
083                    || (r != Void.TYPE)) {
084                throw new NoSuchMethodException();
085            }
086        } catch (final NoSuchMethodException no) {
087            System.out.println("In class " + class_name
088                    + ": public static void main(String[] argv) is not defined");
089            return;
090        }
091        try {
092            method.invoke(null, new Object[] {
093                argv
094            });
095        } catch (final Exception ex) {
096            ex.printStackTrace();
097        }
098    }
099
100
101    /** Default main method used as wrapper, expects the fully qualified class name
102     * of the real class as the first argument.
103     */
104    public static void main( final String[] argv ) throws Exception {
105        /* Expects class name as first argument, other arguments are by-passed.
106         */
107        if (argv.length == 0) {
108            System.out.println("Missing class name.");
109            return;
110        }
111        final String class_name = argv[0];
112        final String[] new_argv = new String[argv.length - 1];
113        System.arraycopy(argv, 1, new_argv, 0, new_argv.length);
114        final JavaWrapper wrapper = new JavaWrapper();
115        wrapper.runMain(class_name, new_argv);
116    }
117}