关于NIO进行socket通信的一个不解的地方

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关于NIO进行socket通信的一个不解的地方 3

服务器端代码：

package nio.tcp;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.CharBuffer;import java.nio.channels.SelectionKey;import java.nio.channels.Selector;import java.nio.channels.ServerSocketChannel;import java.nio.channels.SocketChannel;import java.nio.charset.Charset;import java.nio.charset.CharsetDecoder;import java.util.Iterator;import java.util.Set;public class UnblockServer {	public static void main(String[] args) {		SocketChannel socket = null;		try {			// 打开一个选择器			Selector selector = Selector.open();			// 客户端要使用SocketChannel，对应服务器的ServerSocketChannel			ServerSocketChannel ssc = ServerSocketChannel.open();			// 绑定服务器IP和端口			InetSocketAddress isa = new InetSocketAddress(8710);			ssc.socket().bind(isa);			ssc.configureBlocking(false);			// 向selector注册，要处理的是接收传入事件，所以权限设置为OP_ACCEPT			SelectionKey acceptKey = ssc.register(selector,SelectionKey.OP_ACCEPT);			// 操作？			while (selector.select() > 0) {				Set<SelectionKey> readyKeys = selector.selectedKeys();				Iterator it = readyKeys.iterator();				while (it.hasNext()) {					SelectionKey key = (SelectionKey) it.next();					it.remove();					if (key.isAcceptable()) {						System.out.println("Key is Acceptable");						socket = (SocketChannel) ssc.accept();						socket.configureBlocking(false);						socket.register(selector,								SelectionKey.OP_READ | SelectionKey.OP_WRITE);					}					if (key.isReadable()) {						System.out.println("Key is readable");						socket = (SocketChannel) key.channel();						ByteBuffer buf = ByteBuffer.allocate(1024);						socket.read(buf);						buf.flip();						// 这段实用						Charset charset = Charset.forName("us-ascii");						CharsetDecoder decoder = charset.newDecoder();						CharBuffer charBuffer = decoder.decode(buf);						String result = charBuffer.toString();						System.out.println("Receive Data:" + result);					}					if (key.isWritable()) {						System.out.println("Key is writable");						String msg = "Message from server";						socket = (SocketChannel) key.channel();						//类型转换，实用						Charset set = Charset.forName("us-ascii");						CharsetDecoder dec = set.newDecoder();						CharBuffer charBuf = dec.decode(ByteBuffer.wrap(msg.getBytes()));						System.out.println("Message from server:" + charBuf.toString());						int nBytes = socket.write(ByteBuffer.wrap((charBuf.toString()).getBytes()));					}				}			}		} catch (Exception e) {			e.printStackTrace();		}	}}

客户端代码：

package nio.tcp;import java.io.IOException;import java.net.InetAddress;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.channels.SocketChannel;public class UnblockClient {		public static void main(String[] args) {		try {						InetSocketAddress ia = new InetSocketAddress(InetAddress.getLocalHost(),8710);						//客户端要使用SocketChannel，对应服务器的ServerSocketChannel			SocketChannel client = SocketChannel.open();			client.connect(ia);			//设置为非阻塞，否则就和刚才的程序没啥区别了			client.configureBlocking(false);						//发送数据			sendMessage(client);								} catch (Exception e) {			// TODO Auto-generated catch block			e.printStackTrace();		}	}		public static int sendMessage(SocketChannel client) {		System.out.println("Inside SendMessage");		String msg = null;		ByteBuffer bytebuf;		int nBytes = 0;		try {			msg = "It's message from client!";			System.out.println("msg is "+msg);			bytebuf = ByteBuffer.wrap(msg.getBytes());			for (int i = 0; i < 3; i++) {				nBytes = client.write(bytebuf);				System.out.println(i + " finished");			}			try {				Thread.sleep(5000);			} catch (InterruptedException e) {				// TODO Auto-generated catch block				e.printStackTrace();			}			client.close();			return -1;		} catch (IOException e) {			e.printStackTrace();		}		return nBytes;	 }}

我已经和网上的N多类似程序对照过了，但是我就是弄不明白，为什么客户端明明只是发送了三次数据，而服务器端却会不停地执行write和read操作呢？不是应该执行一次之后就完了的吗？

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