    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.<br>
    027 * Call this wrapper with:
    028 *
    029 * <pre>java org.apache.bcel.util.JavaWrapper &lt;real.class.name&gt; [arguments]</pre>
    030 *
    031 * <p>To use your own class loader you can set the "bcel.classloader" system property<p>
    032 * <pre>java org.apache.bcel.util.JavaWrapper -Dbcel.classloader=foo.MyLoader &lt;real.class.name&gt; [arguments]</pre>
    033 *
    034 * @version $Id$
    035 * @see ClassLoader
    036 */
    037public class JavaWrapper {
    038
    039    private final java.lang.ClassLoader loader;
    040
    041
    042    private static java.lang.ClassLoader getClassLoader() {
    043        final String s = System.getProperty("bcel.classloader");
    044        if ((s == null) || "".equals(s)) {
    045            throw new IllegalArgumentException("The property 'bcel.classloader' must be defined");
    046        }
    047        try {
    048            return (java.lang.ClassLoader) Class.forName(s).newInstance();
    049        } catch (final Exception e) {
    050            throw new RuntimeException(e.toString(), e);
    051        }
    052    }
    053
    054
    055    public JavaWrapper(final java.lang.ClassLoader loader) {
    056        this.loader = loader;
    057    }
    058
    059
    060    public JavaWrapper() {
    061        this(getClassLoader());
    062    }
    063
    064
    065    /** Runs the main method of the given class with the arguments passed in argv
    066     *
    067     * @param class_name the fully qualified class name
    068     * @param argv the arguments just as you would pass them directly
    069     */
    070    public void runMain( final String class_name, final String[] argv ) throws ClassNotFoundException {
    071        final Class<?> cl = loader.loadClass(class_name);
    072        Method method = null;
    073        try {
    074            method = cl.getMethod("main", new Class[] {
    075                argv.getClass()
    076            });
    077            /* Method main is sane ?
    078             */
    079            final int m = method.getModifiers();
    080            final Class<?> r = method.getReturnType();
    081            if (!(Modifier.isPublic(m) && Modifier.isStatic(m)) || Modifier.isAbstract(m)
    082                    || (r != Void.TYPE)) {
    083                throw new NoSuchMethodException();
    084            }
    085        } catch (final NoSuchMethodException no) {
    086            System.out.println("In class " + class_name
    087                    + ": public static void main(String[] argv) is not defined");
    088            return;
    089        }
    090        try {
    091            method.invoke(null, new Object[] {
    092                argv
    093            });
    094        } catch (final Exception ex) {
    095            ex.printStackTrace();
    096        }
    097    }
    098
    099
    100    /** Default main method used as wrapper, expects the fully qualified class name
    101     * of the real class as the first argument.
    102     */
    103    public static void main( final String[] argv ) throws Exception {
    104        /* Expects class name as first argument, other arguments are by-passed.
    105         */
    106        if (argv.length == 0) {
    107            System.out.println("Missing class name.");
    108            return;
    109        }
    110        final String class_name = argv[0];
    111        final String[] new_argv = new String[argv.length - 1];
    112        System.arraycopy(argv, 1, new_argv, 0, new_argv.length);
    113        final JavaWrapper wrapper = new JavaWrapper();
    114        wrapper.runMain(class_name, new_argv);
    115    }
    116}