基于Java NIO的Socket通信

Java NIO模式的Socket通信，是一种同步非阻塞IO设计模式，它为Reactor模式实现提供了基础。

下面看看，Java实现的一个服务端和客户端通信的例子。

NIO模式的基本原理描述如下：

服务端打开一个通道（ServerSocketChannel），并向通道中注册一个选择器（Selector），这个选择器是与一些感兴趣的操作的标识（SelectionKey，即通过这个标识可以定位到具体的操作，从而进行响应的处理）相关联的，然后基于选择器（Selector）轮询通道（ServerSocketChannel）上注册的事件，并进行相应的处理。

客户端在请求与服务端通信时，也可以向服务器端一样注册（比服务端少了一个SelectionKey.OP_ACCEPT操作集合），并通过轮询来处理指定的事件，而不必阻塞。

下面的例子，主要以服务端为例，而客户端只是简单地发送请求数据和读响应数据。

服务端实现，代码如下所示：

package org.shirdrn.java.communications.nio;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;import java.util.logging.Logger;/** * NIO服务端 *  * @author shirdrn */public class NioTcpServer extends Thread {private static final Logger log = Logger.getLogger(NioTcpServer.class.getName());private InetSocketAddress inetSocketAddress;private Handler handler = new ServerHandler();public NioTcpServer(String hostname, int port) {inetSocketAddress = new InetSocketAddress(hostname, port);}@Overridepublic void run() {try {Selector selector = Selector.open(); // 打开选择器ServerSocketChannel serverSocketChannel = ServerSocketChannel.open(); // 打开通道serverSocketChannel.configureBlocking(false); // 非阻塞serverSocketChannel.socket().bind(inetSocketAddress);serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT); // 向通道注册选择器和对应事件标识log.info("Server: socket server started.");while(true) { // 轮询int nKeys = selector.select();if(nKeys>0) {Set<SelectionKey> selectedKeys = selector.selectedKeys();Iterator<SelectionKey> it = selectedKeys.iterator();while(it.hasNext()) {SelectionKey key = it.next();if(key.isAcceptable()) {log.info("Server: SelectionKey is acceptable.");handler.handleAccept(key);} else if(key.isReadable()) {log.info("Server: SelectionKey is readable.");handler.handleRead(key);} else if(key.isWritable()) {log.info("Server: SelectionKey is writable.");handler.handleWrite(key);}it.remove();}}}} catch (IOException e) {e.printStackTrace();}}/** * 简单处理器接口 *  * @author shirdrn */interface Handler {/** * 处理{@link SelectionKey#OP_ACCEPT}事件 * @param key  * @throws IOException */void handleAccept(SelectionKey key) throws IOException;/** * 处理{@link SelectionKey#OP_READ}事件 * @param key  * @throws IOException */void handleRead(SelectionKey key) throws IOException;/** * 处理{@link SelectionKey#OP_WRITE}事件 * @param key  * @throws IOException */void handleWrite(SelectionKey key) throws IOException;}/** * 服务端事件处理实现类 *  * @author shirdrn */class ServerHandler implements Handler {@Overridepublic void handleAccept(SelectionKey key) throws IOException {ServerSocketChannel serverSocketChannel = (ServerSocketChannel)key.channel();SocketChannel socketChannel = serverSocketChannel.accept();log.info("Server: accept client socket " + socketChannel);socketChannel.configureBlocking(false);socketChannel.register(key.selector(), SelectionKey.OP_READ);}@Overridepublic void handleRead(SelectionKey key) throws IOException {ByteBuffer byteBuffer = ByteBuffer.allocate(512);SocketChannel socketChannel = (SocketChannel)key.channel();while(true) {int readBytes = socketChannel.read(byteBuffer);if(readBytes>0) {log.info("Server: readBytes = " + readBytes);log.info("Server: data = " + new String(byteBuffer.array(), 0, readBytes));byteBuffer.flip();socketChannel.write(byteBuffer);break;}}socketChannel.close();}@Overridepublic void handleWrite(SelectionKey key) throws IOException {ByteBuffer byteBuffer = (ByteBuffer) key.attachment();byteBuffer.flip();SocketChannel socketChannel = (SocketChannel)key.channel();socketChannel.write(byteBuffer);if(byteBuffer.hasRemaining()) {key.interestOps(SelectionKey.OP_READ);}byteBuffer.compact();}}public static void main(String[] args) {NioTcpServer server = new NioTcpServer("localhost", 1000);server.start();}}

客户端实现，代码如下所示：

package org.shirdrn.java.communications.nio;import java.io.IOException;import java.net.InetSocketAddress;import java.nio.ByteBuffer;import java.nio.channels.SocketChannel;import java.util.logging.Logger;/** * NIO客户端 *  * @author shirdrn */public class NioTcpClient {private static final Logger log = Logger.getLogger(NioTcpClient.class.getName());private InetSocketAddress inetSocketAddress;public NioTcpClient(String hostname, int port) {inetSocketAddress = new InetSocketAddress(hostname, port);}/** * 发送请求数据 * @param requestData */public void send(String requestData) {try {SocketChannel socketChannel = SocketChannel.open(inetSocketAddress);socketChannel.configureBlocking(false);ByteBuffer byteBuffer = ByteBuffer.allocate(512);socketChannel.write(ByteBuffer.wrap(requestData.getBytes()));while (true) {byteBuffer.clear();int readBytes = socketChannel.read(byteBuffer);if (readBytes > 0) {byteBuffer.flip();log.info("Client: readBytes = " + readBytes);log.info("Client: data = " + new String(byteBuffer.array(), 0, readBytes));socketChannel.close();break;}}} catch (IOException e) {e.printStackTrace();}}public static void main(String[] args) {String hostname = "localhost";String requestData = "Actions speak louder than words!";int port = 1000;new NioTcpClient(hostname, port).send(requestData);}}

上述实现，NioTcpServer服务线程启动后，监听指定端口，等待客户端请求的到来，然后NioTcpClient客户端进程启动并发送请求数据，服务端接收到请求数据后，响应客户端（将请求的数据作为响应数据写回到客户端通道SocketChannel，并等待客户端处理）。

实际上，客户端和服务端可以采用同样轮询的非阻塞模式来实现，为简单实现在这个例子中我们把客户端角色简化了，而实际上它可能在另一个系统通信中充当服务端角色。

另外，上面对于不同事件是采用非线程的方式来处理，只是简单地调用处理的方法。在实际中，如果存在大量连接、读写请求，可以考虑使用线程池来更大程度地并发处理，提高服务端处理的速度和吞吐量，提升系统性能。