NIO

今天研究了NIO（New IO）API上的几个例子代码，并且做了测试。
TimeQuery.java是一个利用NIO进行查询当前主机时间的客户端代码

/*
 * @(#);TimeQuery.java	1.2 01/12/13
 * Ask a list of hosts what time it is.  Demonstrates NIO socket channels
 * (connection and reading);, buffer handling, charsets, and regular
 * expressions.
 *
 * Copyright 2001-2002 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following 
 * conditions are met:
 * 
 * -Redistributions of source code must retain the above copyright  
 * notice, this  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduct the above copyright 
 * notice, this list of conditions and the following disclaimer in 
 * the documentation and/or other materials provided with the 
 * distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of 
 * contributors may be used to endorse or promote products derived 
 * from this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any 
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND 
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY 
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY 
 * DAMAGES OR LIABILITIES  SUFFERED BY LICENSEE AS A RESULT OF  OR 
 * RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR 
 * ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE 
 * FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, 
 * SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER 
 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF 
 * THE USE OF OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that Software is not designed, licensed or 
 * intended for use in the design, construction, operation or 
 * maintenance of any nuclear facility. 
 */

import java.io.*;
import java.net.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.charset.*;
import java.util.regex.*;


public class TimeQuery {

    // The standard daytime port
    private static int DAYTIME_PORT = 13;

    // The port we'll actually use
    private static int port = DAYTIME_PORT;

    // Charset and decoder for US-ASCII
    private static Charset charset = Charset.forName("US-ASCII");;
    private static CharsetDecoder decoder = charset.newDecoder();;

    // Direct byte buffer for reading
    private static ByteBuffer dbuf = ByteBuffer.allocateDirect(1024);;

    // Ask the given host what time it is
    //
    private static void query(String host); throws IOException {
	InetSocketAddress isa
	    = new InetSocketAddress(InetAddress.getByName(host);, port);;
	SocketChannel sc = null;

	try {

	    // Connect
	    sc = SocketChannel.open();;
	    sc.connect(isa);;

	    // Read the time from the remote host.  For simplicity we assume
	    // that the time comes back to us in a single packet, so that we
	    // only need to read once.
/*
clear
public final Buffer clear();
Clears this buffer. The position is set to zero, the limit is set to the capacity, and the mark is discarded. 
Invoke this method before using a sequence of channel-read or put operations to fill this buffer. For example: 

 buf.clear();;     // Prepare buffer for reading
 in.read(buf);;    // Read data
This method does not actually erase the data in the buffer, but it is named as if it did because it will most often be used in situations in which that might as well be the case. 


Returns:
This buffer
*/
	    dbuf.clear();;    
	    sc.read(dbuf);;

	    // Print the remote address and the received time
/*
public final Buffer flip();
Flips this buffer. The limit is set to the current position and then the position is set to zero. If the mark is defined then it is discarded. 
After a sequence of channel-read or put operations, invoke this method to prepare for a sequence of channel-write or relative get operations. For example: 

 buf.put(magic);;    // Prepend header
 in.read(buf);;      // Read data into rest of buffer
 buf.flip();;        // Flip buffer
 out.write(buf);;    // Write header + data to channel
This method is often used in conjunction with the compact method when transferring data from one place to another. 


Returns:
This buffer
*/
	    dbuf.flip();;
	    CharBuffer cb = decoder.decode(dbuf);;
	    System.out.print(isa + " : " + cb);;

	} finally {
	    // Make sure we close the channel (and hence the socket);
	    if (sc != null);
		sc.close();;
	}
    }

    public static void main(String[] args); {
	if (args.length < 1); {
	    System.err.println("Usage: java TimeQuery [port] host...");;
	    return;
	}
	int firstArg = 0;

	// If the first argument is a string of digits then we take that
	// to be the port number
	if (Pattern.matches("[0-9]+", args[0]);); {
	    port = Integer.parseInt(args[0]);;
	    firstArg = 1;
	}

	for (int i = firstArg; i < args.length; i++); {
	    String host = args[i];
	    try {
		query(host);;
	    } catch (IOException x); {
		System.err.println(host + ": " + x);;
	    }
	}
    }

}

NBTimeServer.java 实现了一个非阻塞的网络时间查询服务器

/*
 * @(#);NBTimeServer.java	1.4 01/12/13
 * A non blocking Internet time server implemented using
 * the New I/O (NIO); facilities added to J2SE v 1.4.
 *
 * Copyright 2001-2002 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or 
 * without modification, are permitted provided that the following 
 * conditions are met:
 * 
 * -Redistributions of source code must retain the above copyright  
 * notice, this  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduct the above copyright 
 * notice, this list of conditions and the following disclaimer in 
 * the documentation and/or other materials provided with the 
 * distribution.
 * 
 * Neither the name of Sun Microsystems, Inc. or the names of 
 * contributors may be used to endorse or promote products derived 
 * from this software without specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any 
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND 
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY, 
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY 
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY 
 * DAMAGES OR LIABILITIES  SUFFERED BY LICENSEE AS A RESULT OF  OR 
 * RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR 
 * ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE 
 * FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, 
 * SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER 
 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF 
 * THE USE OF OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN 
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that Software is not designed, licensed or 
 * intended for use in the design, construction, operation or 
 * maintenance of any nuclear facility. 
 */

import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.nio.channels.spi.*;
import java.net.*;
import java.util.*;

// Listen on a port for connections and write back the current time.
public class NBTimeServer {
    private static final int DEFAULT_TIME_PORT = 8900;

    // Constructor with no arguments creates a time server on default port.
    public NBTimeServer(); throws Exception {
	acceptConnections(this.DEFAULT_TIME_PORT);;
    }

    // Constructor with port argument creates a time server on specified port.
    public NBTimeServer(int port); throws Exception {
	acceptConnections(port);;
    }

    // Accept connections for current time. Lazy Exception thrown.
    private static void acceptConnections(int port); throws Exception {
	// Selector for incoming time requests
	Selector acceptSelector = SelectorProvider.provider();.openSelector();;

	// Create a new server socket and set to non blocking mode
	ServerSocketChannel ssc = ServerSocketChannel.open();;
	ssc.configureBlocking(false);;

	// Bind the server socket to the local host and port

	InetAddress lh = InetAddress.getLocalHost();;
	InetSocketAddress isa = new InetSocketAddress(lh, port);;
	ssc.socket();.bind(isa);;
	
	// Register accepts on the server socket with the selector. This
	// step tells the selector that the socket wants to be put on the
	// ready list when accept operations occur, so allowing multiplexed
	// non-blocking I/O to take place.
	SelectionKey acceptKey = ssc.register(acceptSelector, 
					      SelectionKey.OP_ACCEPT);;
	
	int keysAdded = 0;
	
	// Here's where everything happens. The select method will
	// return when any operations registered above have occurred, the
	// thread has been interrupted, etc.
	while ((keysAdded = acceptSelector.select();); > 0); {
	    // Someone is ready for I/O, get the ready keys
	    Set readyKeys = acceptSelector.selectedKeys();;
	    Iterator i = readyKeys.iterator();;

	    // Walk through the ready keys collection and process date requests.
	    while (i.hasNext();); {
		SelectionKey sk = (SelectionKey);i.next();;
		i.remove();;
		// The key indexes into the selector so you
		// can retrieve the socket that's ready for I/O
		ServerSocketChannel nextReady = 
		    (ServerSocketChannel);sk.channel();;
		// Accept the date request and send back the date string
		Socket s = nextReady.accept();.socket();;
		// Write the current time to the socket
                PrintWriter out = new PrintWriter(s.getOutputStream();, true);;
		Date now = new Date();;
		out.println(now);;
		out.close();;
	    }
	}
    }

    // Entry point.
    public static void main(String[] args); {
	// Parse command line arguments and
	// create a new time server (no arguments yet);
	try {
		NBTimeServer nbt = new NBTimeServer();;
	} catch(Exception e); {
		e.printStackTrace();;		
	}
    }
}

评论

1 楼 zzknight 2010-02-08  

代码中出现;; 这样的是有特殊意义的吗？