naming.java

《移动Agent技术》一书的所有章节源代码。

/*
 * @(#)Naming.java	1.4 96/11/18
 * 
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.1_beta
 */
package java.rmi;

import java.rmi.registry.*;
import java.net.URL;
import java.net.MalformedURLException;

/**
 * This is the bootstrap mechanism for obtaining references to remote
 * objects based on Uniform Resource Locator (URL) syntax.  The URL
 * for a remote object is specified using the usual host, port and
 * name:
 *<br>	rmi://host:port/name
 *<br>	host = host name of registry  (defaults to current host)
 *<br>	port = port number of registry (defaults to the registry port number)
 *<br>  name = name for remote object
 */
public final class Naming {
    /*
     * Disallow anyone from creating one of these
     */
    private Naming() {}

    /**
     * Returns the remote object for the URL.
     * @exception RemoteException If registry could not be contacted.
     * @exception NotBoundException If name is not currently bound.
     */
    public static Remote lookup(String name)
	throws NotBoundException,
	    java.net.MalformedURLException,
	    UnknownHostException,
	    RemoteException
    {
	URL url = cleanURL(name);
	Registry registry = getRegistry(url);

	String file = getName(url);
	if (file == null)
	    return registry;
	return registry.lookup(file);
    }
    
    /**
     * Binds the name to the specified remote object.
     * @exception RemoteException If registry could not be contacted.
     * @exception AlreadyBoundException If name is already bound.
     */
    public static void bind(String name, Remote obj)
	throws AlreadyBoundException,
	    java.net.MalformedURLException,
	    UnknownHostException,
	    RemoteException
    {
	URL url = cleanURL(name);
	Registry registry = getRegistry(url);

	if (obj == null)
	    throw new NullPointerException("cannot bind to null");

	registry.bind(getName(url), obj);
    }
    
    /**
     * Unbind the name.
     * @exception RemoteException If registry could not be contacted.
     * @exception NotBoundException If name is not currently bound.
     */
    public static void unbind(String name)
	throws RemoteException,
	    NotBoundException,
	    java.net.MalformedURLException,
	    UnknownHostException
    {
	URL url = cleanURL(name);
	Registry registry = getRegistry(url);

	registry.unbind(getName(url));
    }

    /** 
     * Rebind the name to a new object; replaces any existing binding.
     * @exception RemoteException If registry could not be contacted.
     */
    public static void rebind(String name, Remote obj)
	throws RemoteException,
	    java.net.MalformedURLException,
	    UnknownHostException
    {
	URL url = cleanURL(name);
	Registry registry = getRegistry(url);

	if (obj == null)
	    throw new NullPointerException("cannot bind to null");

	registry.rebind(getName(url), obj);
    }
    
    /**
     * Returns an array of strings of the URLs in the registry.
     * The array contains a snapshot of the names present in the registry.
     * @exception RemoteException If registry could not be contacted.
     */
    public static String[] list(String name)
	throws RemoteException,
	    java.net.MalformedURLException,
	    UnknownHostException
    {
	URL url = cleanURL(name);
	Registry registry = getRegistry(url);

	String host = url.getHost();
	int port = url.getPort();

	String prefix = "rmi:";
 	if (port > 0 || !host.equals(""))
	    prefix += "//" + host;
	if (port > 0)
	    prefix += ":" + port;
	prefix += "/";

	String[] names = registry.list();
	for (int i = 0; i < names.length; i++) {
	    names[i] = prefix + names[i];
	}
	return names;
    }

    /** Function to find registry from URL
     */
    private static Registry getRegistry(URL url)
	throws RemoteException, UnknownHostException
    {
	String host = url.getHost();
	int port = url.getPort();

	return LocateRegistry.getRegistry(host, port);
    }

    /** Function to extract only the name from the URL.
     */
    private static String getName(URL url)
    {
	String name = url.getFile();
	if (name == null || name.equals("/"))
	    return null;
	return name.substring(1);
    }

    /**
     * Function to cleanup and create the URL.
     * It checks for and removes the protocol
     */
    private static URL cleanURL(String name) 
	throws java.net.MalformedURLException
    {
	URL url = new URL("file:");

	// remove the approved protocol
	if (name.startsWith("rmi:"))
	    name = name.substring(4);

	// No protocol must remain
	int colon = name.indexOf(':');
	if (colon >= 0 && colon < name.indexOf('/') )
	    throw new java.net.MalformedURLException("Protocol should be rmi:");

	url = new URL(url, name);
	return url;
    }
}