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
023import org.apache.commons.lang3.StringUtils;
024
025/**
026 * Java interpreter replacement, i.e., wrapper that uses its own ClassLoader to modify/generate classes as they're
027 * requested. You can take this as a template for your own applications.
028 * <p>
029 * Call this wrapper with:
030 * </p>
031 *
032 * <pre>
033 * java org.apache.bcel.util.JavaWrapper &lt;real.class.name&gt; [arguments]
034 * </pre>
035 * <p>
036 * To use your own class loader you can set the "bcel.classloader" system property.
037 * </p>
038 *
039 * <pre>
040 * java org.apache.bcel.util.JavaWrapper -Dbcel.classloader=foo.MyLoader &lt;real.class.name&gt; [arguments]
041 * </pre>
042 *
043 * @see ClassLoader
044 */
045public class JavaWrapper {
046
047    private static java.lang.ClassLoader getClassLoader() {
048        final String s = System.getProperty("bcel.classloader");
049        if (StringUtils.isEmpty(s)) {
050            throw new IllegalStateException("The property 'bcel.classloader' must be defined");
051        }
052        try {
053            return (java.lang.ClassLoader) Class.forName(s).newInstance();
054        } catch (final Exception e) {
055            throw new IllegalStateException(e.toString(), e);
056        }
057    }
058
059    /**
060     * Default main method used as wrapper, expects the fully qualified class name of the real class as the first argument.
061     */
062    public static void main(final String[] argv) throws Exception {
063        /*
064         * Expects class name as first argument, other arguments are by-passed.
065         */
066        if (argv.length == 0) {
067            System.out.println("Missing class name.");
068            return;
069        }
070        final String className = argv[0];
071        final String[] newArgv = new String[argv.length - 1];
072        System.arraycopy(argv, 1, newArgv, 0, newArgv.length);
073        new JavaWrapper().runMain(className, newArgv);
074    }
075
076    private final java.lang.ClassLoader loader;
077
078    public JavaWrapper() {
079        this(getClassLoader());
080    }
081
082    public JavaWrapper(final java.lang.ClassLoader loader) {
083        this.loader = loader;
084    }
085
086    /**
087     * Runs the main method of the given class with the arguments passed in argv
088     *
089     * @param className the fully qualified class name
090     * @param argv the arguments just as you would pass them directly
091     */
092    public void runMain(final String className, final String[] argv) throws ClassNotFoundException {
093        final Class<?> cl = loader.loadClass(className);
094        Method method = null;
095        try {
096            method = cl.getMethod("main", argv.getClass());
097            /*
098             * Method main is sane ?
099             */
100            final int m = method.getModifiers();
101            final Class<?> r = method.getReturnType();
102            if (!(Modifier.isPublic(m) && Modifier.isStatic(m)) || Modifier.isAbstract(m) || r != Void.TYPE) {
103                throw new NoSuchMethodException();
104            }
105        } catch (final NoSuchMethodException no) {
106            System.out.println("In class " + className + ": public static void main(String[] argv) is not defined");
107            return;
108        }
109        try {
110            method.invoke(null, (Object[]) argv);
111        } catch (final Exception ex) {
112            ex.printStackTrace();
113        }
114    }
115}