使用 NIO 实现 echo 服务器

NIO相关知识点

IO、NIO、AIO 内部原理分析
NIO 之 Selector实现原理
NIO 之 Channel实现原理
NIO 之 ByteBuffer实现原理

服务器使用NIO来实现一个echo协议的服务器。
echo协议简单也很有用，可以测试网络连接。

消息的格式为：消息长度（int）+消息内容

通过消息长度来进行socket分包，防止读取出现半包、粘包等问题。

服务端

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;public class NioEchoServer {public static void server() {ServerSocketChannel ssc = null;Selector selector = null;try {ssc = ServerSocketChannel.open();//设置为非阻塞ssc.configureBlocking(false);ssc.bind(new InetSocketAddress(9000), 10);selector = Selector.open();ssc.register(selector, SelectionKey.OP_ACCEPT);} catch (IOException e) {e.printStackTrace();}while (true) {try {selector.select();} catch (IOException e) {e.printStackTrace();}try {Set set = selector.selectedKeys();Iterator it = set.iterator();while (it.hasNext()) {SelectionKey key = it.next();set.remove(key);try {if (key.isAcceptable()) {ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();SocketChannel clientChannel = serverChannel.accept();clientChannel.configureBlocking(false);MessageInfo messageInfo = new MessageInfo();clientChannel.register(selector, SelectionKey.OP_READ, messageInfo);} else if (key.isReadable()) {SocketChannel clientChannel = (SocketChannel) key.channel();MessageInfo messageInfo = (MessageInfo)key.attachment();if(messageInfo.getLenBuf() == null){messageInfo.setLenBuf(ByteBuffer.allocate(4));}//消息长度int len = messageInfo.getLen();//判断消息长度是否读取完成if(len!=-1){if(messageInfo.contentBuf == null){//创建指定消息长度的bufmessageInfo.contentBuf = ByteBuffer.allocate(len);}//如果消息未读取完成，继续读取if(messageInfo.contentBuf.position()if(clientChannel.read(messageInfo.contentBuf)==-1){clientChannel.register(selector, SelectionKey.OP_WRITE, messageInfo);}}if(len==0){System.out.println("空消息");key.cancel();key.channel().close();}else if(messageInfo.contentBuf.position()==len){messageInfo.contentBuf.flip();System.out.println(new String(messageInfo.contentBuf.array()));
//                                  clientChannel.register(selector, SelectionKey.OP_WRITE, messageInfo);key.interestOps(SelectionKey.OP_WRITE);}}//消息长度未读取完成else{int i = clientChannel.read(messageInfo.getLenBuf());if(i==-1){System.out.println("消息异常:"+messageInfo.getLenBuf());break;}if(messageInfo.getLenBuf().position()==4){messageInfo.getLenBuf().flip();messageInfo.setLen(messageInfo.getLenBuf().getInt());}}}else if(key.isWritable()){SocketChannel clientChannel = (SocketChannel) key.channel();MessageInfo messageInfo = (MessageInfo)key.attachment();messageInfo.lenBuf.rewind();messageInfo.contentBuf.rewind();ByteBuffer[] bufs = new ByteBuffer[]{messageInfo.lenBuf, messageInfo.contentBuf};System.out.println(messageInfo.contentBuf.limit()+":"+messageInfo.contentBuf.capacity());clientChannel.write(bufs);key.cancel();key.channel().close();}} catch (Exception e) {key.cancel();key.channel().close();}}} catch (Exception e) {e.printStackTrace();break;}}System.out.println("");}public static void main(String[] args) {server();}//消息对象static class MessageInfo {private int len=-1;private ByteBuffer lenBuf;private ByteBuffer contentBuf;public int getLen() {return len;}public void setLen(int len) {this.len = len;}public ByteBuffer getLenBuf() {return lenBuf;}public void setLenBuf(ByteBuffer lenBuf) {this.lenBuf = lenBuf;}public ByteBuffer getContentBuf() {return contentBuf;}public void setContentBuf(ByteBuffer contentBuf) {this.contentBuf = contentBuf;}}}

客户端

import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SocketChannel;public class NioEchoClient {public static void main(String[] args) {SocketAddress sa = new InetSocketAddress("127.0.0.1", 9000);try {SocketChannel client = SocketChannel.open(sa);byte[] data = "大家好".getBytes();ByteBuffer lenBuf = ByteBuffer.wrap(int2byte(data.length));ByteBuffer textBuf = ByteBuffer.wrap(data);ByteBuffer[] bufArray = new ByteBuffer[]{lenBuf, textBuf};client.write(bufArray);lenBuf.clear();textBuf.clear();client.read(bufArray);System.out.println("echo:"+new String(textBuf.array()));client.close();} catch (IOException e) {e.printStackTrace();}}/*** int 转 byte[] 数组* @param len* @return*/public static byte[] int2byte(int len) {byte[] b = new byte[4];b[0] = (byte) (len >> 24);b[1] = (byte) (len >> 16 & 0XFF);b[2] = (byte) (len >> 8 & 0XFF);b[3] = (byte) (len & 0XFF);return b;}
}

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