    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 */
    017package org.apache.bcel.util;
    018
    019import java.lang.reflect.Method;
    020import java.lang.reflect.Modifier;
    021
    022import org.apache.commons.lang3.StringUtils;
    023
    024/**
    025 * Java interpreter replacement, i.e., wrapper that uses its own ClassLoader to modify/generate classes as they're
    026 * requested. You can take this as a template for your own applications.
    027 * <p>
    028 * Call this wrapper with:
    029 * </p>
    030 *
    031 * <pre>
    032 * java org.apache.bcel.util.JavaWrapper &lt;real.class.name&gt; [arguments]
    033 * </pre>
    034 * <p>
    035 * To use your own class loader you can set the "bcel.classloader" system property.
    036 * </p>
    037 *
    038 * <pre>
    039 * java org.apache.bcel.util.JavaWrapper -Dbcel.classloader=foo.MyLoader &lt;real.class.name&gt; [arguments]
    040 * </pre>
    041 *
    042 * @see ClassLoader
    043 */
    044public class JavaWrapper {
    045
    046    private static java.lang.ClassLoader getClassLoader() {
    047        final String s = System.getProperty("bcel.classloader");
    048        if (StringUtils.isEmpty(s)) {
    049            throw new IllegalStateException("The property 'bcel.classloader' must be defined");
    050        }
    051        try {
    052            return (java.lang.ClassLoader) Class.forName(s).getConstructor().newInstance();
    053        } catch (final Exception e) {
    054            throw new IllegalStateException(e.toString(), e);
    055        }
    056    }
    057
    058    /**
    059     * Default main method used as wrapper, expects the fully qualified class name of the real class as the first argument.
    060     */
    061    public static void main(final String[] argv) throws Exception {
    062        /*
    063         * Expects class name as first argument, other arguments are by-passed.
    064         */
    065        if (argv.length == 0) {
    066            System.out.println("Missing class name.");
    067            return;
    068        }
    069        final String className = argv[0];
    070        final String[] newArgv = new String[argv.length - 1];
    071        System.arraycopy(argv, 1, newArgv, 0, newArgv.length);
    072        new JavaWrapper().runMain(className, newArgv);
    073    }
    074
    075    private final java.lang.ClassLoader loader;
    076
    077    public JavaWrapper() {
    078        this(getClassLoader());
    079    }
    080
    081    public JavaWrapper(final java.lang.ClassLoader loader) {
    082        this.loader = loader;
    083    }
    084
    085    /**
    086     * Runs the main method of the given class with the arguments passed in argv
    087     *
    088     * @param className the fully qualified class name
    089     * @param argv the arguments just as you would pass them directly
    090     * @throws ClassNotFoundException if {@code className} can't be found.
    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}