Java interpreter replacement : ClassLoader « Reflection « Java

Java interpreter replacement

 * Copyright  2000-2004 The Apache Software Foundation
 *  Licensed under the Apache License, Version 2.0 (the "License"); 
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License. 

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;

 * Java interpreter replacement, i.e., wrapper that uses its own ClassLoader to
 * modify/generate classes as they're requested. You can take this as a template
 * for your own applications.<br>
 * Call this wrapper with
 * @version $Id: 386056 2006-03-15 11:31:56Z tcurdt $
 * @author <A HREF="">M. Dahm</A>
 * @see ClassLoader
public class JavaWrapper {

  private java.lang.ClassLoader loader;

  private static java.lang.ClassLoader getClassLoader() {
    String s = System.getProperty("bcel.classloader");
    if ((s == null) || "".equals(s)) {
      s = "org.apache.bcel.util.ClassLoader";
    try {
      return (java.lang.ClassLoader) Class.forName(s).newInstance();
    } catch (Exception e) {
      throw new RuntimeException(e.toString());

  public JavaWrapper(java.lang.ClassLoader loader) {
    this.loader = loader;

  public JavaWrapper() {

   * Runs the main method of the given class with the arguments passed in argv
   * @param class_name
   *          the fully qualified class name
   * @param argv
   *          the arguments just as you would pass them directly
  public void runMain(String class_name, String[] argv) throws ClassNotFoundException {
    Class cl = loader.loadClass(class_name);
    Method method = null;
    try {
      method = cl.getMethod("main", new Class[] { argv.getClass() });
       * Method main is sane ?
      int m = method.getModifiers();
      Class r = method.getReturnType();
      if (!(Modifier.isPublic(m) && Modifier.isStatic(m)) || Modifier.isAbstract(m)
          || (r != Void.TYPE)) {
        throw new NoSuchMethodException();
    } catch (NoSuchMethodException no) {
      System.out.println("In class " + class_name
          + ": public static void main(String[] argv) is not defined");
    try {
      method.invoke(null, new Object[] { argv });
    } catch (Exception ex) {

   * Default main method used as wrapper, expects the fully qualified class name
   * of the real class as the first argument.
  public static void main(String[] argv) throws Exception {
     * Expects class name as first argument, other arguments are by-passed.
    if (argv.length == 0) {
      System.out.println("Missing class name.");
    String class_name = argv[0];
    String[] new_argv = new String[argv.length - 1];
    System.arraycopy(argv, 1, new_argv, 0, new_argv.length);
    JavaWrapper wrapper = new JavaWrapper();
    wrapper.runMain(class_name, new_argv);


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3.Dynamically Reloading a Modified Class
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15.Class For Name
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