/** * Copyright 2006 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 * *     http://www.apache.org/licenses/LICENSE-2.0 * * 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. */package org.apache.hadoop.examples;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.TreeMap;import java.util.Iterator;import java.util.Map;import java.util.Map.Entry;public class ExampleDriver {    /**   * A description of an example program based on its class and a    * human-readable description.   * @author Owen O'Malley   * @date feb 2006   */  static private class ProgramDescription {        static final Class[] paramTypes = new Class[] {String[].class};        /**     * Create a description of an example program.     * @param mainClass the class with the main for the example program     * @param description a string to display to the user in help messages     * @throws SecurityException if we can't use reflection     * @throws NoSuchMethodException if the class doesn't have a main method     */    public ProgramDescription(Class mainClass,                               String description)    throws SecurityException, NoSuchMethodException {      this.main = mainClass.getMethod("main", paramTypes);      this.description = description;    }        /**     * Invoke the example application with the given arguments     * @param args the arguments for the application     * @throws Throwable The exception thrown by the invoked method     */    public void invoke(String[] args)    throws Throwable {      try {        main.invoke(null, new Object[]{args});      } catch (InvocationTargetException except) {        throw except.getCause();      }    }        public String getDescription() {      return description;    }        private Method main;    private String description;  }    private static void printUsage(Map programs) {    System.out.println("Valid program names are:");    for(Iterator itr=programs.entrySet().iterator(); itr.hasNext();) {      Map.Entry item = (Entry) itr.next();      System.out.println("  " + (String) item.getKey() + ": " +          ((ProgramDescription) item.getValue()).getDescription());    }     }    /**   * This is a driver for the example programs.   * It looks at the first command line argument and tries to find an   * example program with that name.   * If it is found, it calls the main method in that class with the rest    * of the command line arguments.   * @param args The argument from the user. args[0] is the command to run.   * @throws NoSuchMethodException    * @throws SecurityException    * @throws IllegalAccessException    * @throws IllegalArgumentException    * @throws Throwable Anything thrown by the example program's main   */  public static void main(String[] args)   throws Throwable   {    Map programs = new TreeMap();        // Add new programs to this list    programs.put("wordcount", new ProgramDescription(WordCount.class,    "A map/reduce program that counts the words in the input files."));    programs.put("grep", new ProgramDescription(Grep.class,    "A map/reduce program that counts the matches of a regex in the input."));        // Make sure they gave us a program name.    if (args.length == 0) {      System.out.println("An example program must be given as the" +           " first argument.");      printUsage(programs);      return;    }        // And that it is good.    ProgramDescription pgm = (ProgramDescription) programs.get(args[0]);    if (pgm == null) {      System.out.println("Unknown program '" + args[0] + "' chosen.");      printUsage(programs);      return;    }        // Remove the leading argument and call main    String[] new_args = new String[args.length - 1];    for(int i=1; i < args.length; ++i) {      new_args[i-1] = args[i];    }    pgm.invoke(new_args);  }  }