下面是NIO编程的一个简单的demo ，总共包括四部分，Client，ClientHandler，Server和ServerHandler首先是Server端，NIO的server端的通信序列图如下图：
Server 的两部分代码如下： Server主类比简单，设定端口号和serverHandler线程；
package MyTestNetty.Server; /** * Created by User on 2017/8/4. */ public class TimeServer { public static void main(String[] args) { int port = 8080; MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port); new Thread(timeServer,"myNIo server").start(); } }第二部分是ServerHandler部分代码如下：
package MyTestNetty.Server; import java.io.IOException; import java.net.InetSocketAddress; 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; /** * Created by User on 2017/8/4. */ public class MultiplexerTimeServer implements Runnable { private Selector selector; private ServerSocketChannel serverSocketChannel; private volatile boolean stop; public MultiplexerTimeServer(int port){ try { selector = Selector.open(); serverSocketChannel = ServerSocketChannel.open(); serverSocketChannel.configureBlocking(false); serverSocketChannel.socket().bind(new InetSocketAddress(port),1024); serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT); System.out.println("the time server start in port :"+ port); } catch (IOException e) { e.printStackTrace(); } } public void stop(){ this.stop =true; } @Override public void run() { while(!stop){//循环遍历selector,休眠时间为1S,当又处于就绪状态的CHannel时，selector将返回该channel的集合。通过对Channel集合的迭代，可进行网络异步读写操作 try { selector.select(1000); Set<SelectionKey> selectKeys = selector.selectedKeys(); Iterator<SelectionKey> it = selectKeys.iterator(); SelectionKey key = null; while (it.hasNext()){ key = it.next(); it.remove(); handleInput(key); } } catch (IOException e) { e.printStackTrace(); } } //多路复用器关闭后，所注册在上面的Channel和Pipe等资源会被自动去注册并关闭，所以不需要重复释放资源 if(selector!=null){ try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } } private void handleInput(SelectionKey key) throws IOException { if(key.isValid()){ if(key.isAcceptable()){//通过SelectionKey的操作位判断其事件的类型 ServerSocketChannel ssc =(ServerSocketChannel) key.channel();// try { SocketChannel sc =ssc.accept();//创建SocketChannel实例 sc.configureBlocking(false); sc.register(selector,SelectionKey.OP_READ); } catch (IOException e) { e.printStackTrace(); } } if(key.isReadable()){//读取客户端请求 SocketChannel sc = (SocketChannel)key.channel(); ByteBuffer readbuffer = ByteBuffer.allocate(1024); try { int readBytes = sc.read(readbuffer); if(readBytes>0){ readbuffer.flip(); byte[] bytes = new byte[readbuffer.remaining()]; readbuffer.get(bytes); String body = new String(bytes,"UTF-8"); System.out.println("Hello，glad to see you :"+body); String current = "QUERY TIME ORDER".equalsIgnoreCase(body)?new java.util.Date(System.currentTimeMillis()).toString():"BAD ORDER"; doWrite(sc," server"); }else{ key.cancel(); sc.close(); } } catch (IOException e) {//如果在catch中不添加key.cancel将会一直不停的抛出这个异常 key.cancel(); sc.socket().close(); sc.close(); System.out.println("execption handled"); //e.printStackTrace(); } } } } private void doWrite(SocketChannel sc, String current) throws IOException {// if(current!=null&¤t.toString().trim().length()>0){ byte[] bytes = current.getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length); writeBuffer.put(bytes); writeBuffer.flip(); sc.write(writeBuffer); } } }这一部分主要是包括监听客户端发送过来的请求，selector循环检查是否有channel就绪，如果有就绪的channel就将其的selectionKey选出进行IO读写，启动运行后可输出一下结果表示服务端启动成功
注意这一部分代码在90多行左右，这部分代码如果去掉，运行之后会不断的抛出异常：
catch (IOException e) {//如果在catch中不添加key.cancel将会一直不停的抛出这个异常 key.cancel(); sc.socket().close(); sc.close(); System.out.println("execption handled"); //e.printStackTrace(); }如果去掉之后会抛出一下异常：
这是因为客户端异常关闭后，服务器的选择器会获取到与客户端套接字对应的套接字通道SelectionKey，并且这个key的兴趣是OP_READ，执行从这个通道读取数据时，客户端已套接字已关闭，所以会出现“java.io.IOException: 远程主机强迫关闭了一个现有的连接”的错误。所以在catch中要进行处理，即取消当前key并关闭通道。
