programdriver.java

hadoop:Nutch集群平台

/**
 * 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.util;

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;

/** A driver that is used to run programs added to it
 */

public class ProgramDriver {
    
    /**
     * A description of a program based on its class and a 
     * human-readable description.
     * @author Owen O'Malley
     * @date april 2006
     */
     Map programs;
     
     public ProgramDriver(){
        programs = new TreeMap();
     }
     
    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 the method that adds the classed to the repository
     * @param name The name of the string you want the class instance to be called with
     * @param mainClass The class that you want to add to the repository
     * @param description The description of the class
     * @throws NoSuchMethodException 
     * @throws SecurityException 
     */
    public void addClass (String name, Class mainClass, String description) throws Throwable {
	programs.put(name , new ProgramDescription(mainClass, description));
    }
    
    /**
     * 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 void driver(String[] args) 
	throws Throwable 
    {
	// 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);
    }
    
}