tcp nio 远程主机强迫关闭了一个现有的连接

import java.io.IOException;

import java.net.InetSocketAddress;

import java.net.ServerSocket;

import java.net.SocketAddress;

import java.nio.ByteBuffer;

import java.nio.channels.SelectionKey;

import java.nio.channels.Selector;

import java.nio.channels.ServerSocketChannel;

import java.nio.channels.SocketChannel;

import java.util.Iterator;

import java.util.Set;

public class NIOServer implements Runnable {
<span class="hljs-comment">/*标识数字*/</span>
<span class="hljs-keyword">private</span>  <span class="hljs-keyword">int</span> flag = <span class="hljs-number">0</span>;
<span class="hljs-comment">/*缓冲区大小*/</span>
<span class="hljs-keyword">private</span>  <span class="hljs-keyword">int</span> BLOCK = <span class="hljs-number">4096</span>;
<span class="hljs-comment">/*接受数据缓冲区*/</span>
<span class="hljs-keyword">private</span>  ByteBuffer sendbuffer = ByteBuffer.allocate(BLOCK);
<span class="hljs-comment">/*发送数据缓冲区*/</span>
<span class="hljs-keyword">private</span>  ByteBuffer receivebuffer = ByteBuffer.allocate(BLOCK);
<span class="hljs-keyword">private</span>  Selector selector;

<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-title">NIOServer</span><span class="hljs-params">(<span class="hljs-keyword">int</span> port)</span></span>{
	<span class="hljs-keyword">try</span>{
	<span class="hljs-comment">// 打开服务器套接字通道</span>
		ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
	<span class="hljs-comment">// 服务器配置为非阻塞</span>
		serverSocketChannel.configureBlocking(<span class="hljs-keyword">false</span>);
	<span class="hljs-comment">// 检索与此通道关联的服务器套接字</span>
		ServerSocket serverSocket = serverSocketChannel.socket();
	<span class="hljs-comment">// 进行服务的绑定</span>
		serverSocket.bind(<span class="hljs-keyword">new</span> InetSocketAddress(port));
	<span class="hljs-comment">// 通过open()方法找到Selector</span>
		selector = Selector.open();
	<span class="hljs-comment">// 注册到selector，等待连接</span>
		serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
		System.out.println(<span class="hljs-string">"Server Start----8888:"</span>);
	}<span class="hljs-keyword">catch</span>(Exception e){
		e.printStackTrace();
	}
}

<span class="hljs-comment">// 监听</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">run</span><span class="hljs-params">()</span> </span>{
	<span class="hljs-keyword">try</span> {
		<span class="hljs-keyword">while</span> (<span class="hljs-keyword">true</span>) {
			<span class="hljs-comment">// 选择一组键，并且相应的通道已经打开</span>
			selector.select();
			<span class="hljs-comment">// 返回此选择器的已选择键集。</span>
			Set&lt;SelectionKey&gt; selectionKeys = selector.selectedKeys();
			Iterator&lt;SelectionKey&gt; iterator = selectionKeys.iterator();
			<span class="hljs-keyword">while</span> (iterator.hasNext()) {
				SelectionKey selectionKey = iterator.next();
				iterator.remove();
				<span class="hljs-keyword">try</span>{
					handleKey(selectionKey);

				}<span class="hljs-keyword">catch</span>(IOException e){
					e.printStackTrace();
					<span class="hljs-comment">//selectionKey.cancel();</span>
					<span class="hljs-keyword">break</span>;
				}
			}
		}
	} <span class="hljs-keyword">catch</span> (Exception e) {
		e.printStackTrace();
	}
}

<span class="hljs-comment">// 处理请求</span>
<span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-keyword">void</span> <span class="hljs-title">handleKey</span><span class="hljs-params">(SelectionKey selectionKey)</span> <span class="hljs-keyword">throws</span> IOException </span>{
	<span class="hljs-comment">// 接受请求</span>
	ServerSocketChannel server = <span class="hljs-keyword">null</span>;
	SocketChannel client = <span class="hljs-keyword">null</span>;
	SocketAddress clientaddr = <span class="hljs-keyword">null</span>;
	String receiveText;
	String sendText;
	<span class="hljs-keyword">int</span> count=<span class="hljs-number">0</span>;

	<span class="hljs-comment">// 测试此键的通道是否已准备好接受新的套接字连接。</span>

	<span class="hljs-keyword">if</span> (selectionKey.isAcceptable()) {
		<span class="hljs-comment">// 返回为之创建此键的通道。</span>
		server = (ServerSocketChannel) selectionKey.channel();
		<span class="hljs-comment">// 接受到此通道套接字的连接。</span>
		<span class="hljs-comment">// 此方法返回的套接字通道（如果有）将处于阻塞模式。</span>
		client = server.accept();
		clientaddr=client.socket().getRemoteSocketAddress();
		System.out.printf(<span class="hljs-string">"+++++++++++服务器端接受客户端[%s]连接!+++++++++++ \n"</span>,clientaddr);
		<span class="hljs-comment">// 配置为非阻塞</span>
		client.configureBlocking(<span class="hljs-keyword">false</span>);
		<span class="hljs-comment">// 注册到selector，等待连接</span>
		client.register(selector, SelectionKey.OP_READ);
	} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (selectionKey.isReadable()) {

			<span class="hljs-comment">// 返回为之创建此键的通道。</span>
			client = (SocketChannel) selectionKey.channel();
			clientaddr=client.socket().getRemoteSocketAddress();
			<span class="hljs-comment">//将缓冲区清空以备下次读取</span>
			receivebuffer.clear();

			<span class="hljs-comment">//读取服务器发送来的数据到缓冲区中</span>
			count = client.read(receivebuffer);
			<span class="hljs-keyword">if</span> (count &gt; <span class="hljs-number">0</span>) {
				receiveText = <span class="hljs-keyword">new</span> String( receivebuffer.array(),<span class="hljs-number">0</span>,count);
				System.out.printf(<span class="hljs-string">"服务器端接受客户端[%s]数据:\n%s"</span>,clientaddr,receiveText);
				client.register(selector, SelectionKey.OP_WRITE);
			}

	} <span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (selectionKey.isWritable()) {
		<span class="hljs-comment">//将缓冲区清空以备下次写入</span>
		sendbuffer.clear();
		<span class="hljs-comment">// 返回为之创建此键的通道。</span>
		client = (SocketChannel) selectionKey.channel();
		sendText=<span class="hljs-string">"message from server--"</span> + flag++;
		<span class="hljs-comment">//向缓冲区中输入数据</span>
		sendbuffer.put(sendText.getBytes());
		 <span class="hljs-comment">//将缓冲区各标志复位,因为向里面put了数据标志被改变要想从中读取数据发向服务器,就要复位</span>
		sendbuffer.flip();
		<span class="hljs-comment">//输出到通道</span>
		client.write(sendbuffer);
		System.out.println(<span class="hljs-string">"服务器端向客户端发送数据--："</span>+sendText);
		client.register(selector, SelectionKey.OP_READ);
	}
}

<span class="hljs-comment">/**
 * <span class="hljs-doctag">@param</span> args
 * <span class="hljs-doctag">@throws</span> IOException
 */</span>
<span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">void</span> <span class="hljs-title">main</span><span class="hljs-params">(String[] args)</span> <span class="hljs-keyword">throws</span> IOException </span>{
	<span class="hljs-comment">// TODO Auto-generated method stub</span>
	<span class="hljs-keyword">int</span> port = <span class="hljs-number">8888</span>;
	NIOServer server = <span class="hljs-keyword">new</span> NIOServer(port);
	server.run();
}

}

上面是从网上摘录的Java NIO TCP 的一个server程序，用客户端的NIO TCP与之连接的时候，只要客户端断开连接，服务器端就会报出“远程主机强迫关闭了一个现有的连接”的错误，并且中断服务器端程序。经过查阅之后发现，得知“OP_READ
事件不仅仅只有可读时才触发，当channel中数据读完远程的另一端被关闭有一个错误的pending都会触发OP_READ事件"!

解决办法：在selectionKey.isReadable()中加入错误捕捉机制，即：

if (selectionKey.isReadable()) {
try {
// 返回为之创建此键的通道。
client = (SocketChannel) selectionKey.channel();
clientaddr=client.socket().getRemoteSocketAddress();
//将缓冲区清空以备下次读取
receivebuffer.clear();
//读取服务器发送来的数据到缓冲区中
count = client.read(receivebuffer);
if (count > 0) {
receiveText = new String( receivebuffer.array(),0,count);
System.out.printf("服务器端接受客户端[%s]数据:\n%s",clientaddr,receiveText);
client.register(selector, SelectionKey.OP_WRITE);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
selectionKey.cancel();  //取消selectionKey
}

 就可以捕获异常，使服务器程序不会因为某一个客户端的断开而中断.