tcp socket实例（改进）
上一篇的程序服务器端只能接受一个客户端请求，本篇改为模拟多客户端程序
客户端：

package socket;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.Socket;import java.net.UnknownHostException;public class MultiClient {public static void main(String[] args) {MultiClient mc = new MultiClient();mc.sendSubsequentRequest();}private void sendSubsequentRequest() {for(int i=0;i<100;i++){ //模拟多个并发用户向客户端同时发送请求，其实在一台机子上还是有先后顺序的new Thread(new RequestSender()).start();}}}class RequestSender implements Runnable {@Overridepublic void run() {try {callServer();} catch (UnknownHostException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}private void callServer() throws UnknownHostException, IOException {int reqInt = 23;Socket s = new Socket("localhost", 8888); // 客户端给出IP和端口号InputStream is = s.getInputStream();OutputStream os = s.getOutputStream();DataInputStream dis = new DataInputStream(is);DataOutputStream dos = new DataOutputStream(os);dos.writeInt(reqInt);dos.flush();int serverInt = dis.readInt();System.out.println("server answer " + reqInt + "*18 = " + serverInt);dis.close();dos.close();}}

服务器端：
只是加了一个while循环

package socket;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;//简单的处理多客户端public class MultiServer {public MultiServer() {}public static void main(String[] args) {MultiServer ms = new MultiServer();try {ms.listen(8888);} catch (IOException e) {e.printStackTrace();}}private void listen(int port) throws IOException {ServerSocket server = new ServerSocket(port);while (true) {Socket socket = server.accept();InputStream is = socket.getInputStream();OutputStream os = socket.getOutputStream();DataInputStream dis = new DataInputStream(is);DataOutputStream dos = new DataOutputStream(os);int receiveInt = dis.readInt(); // 读取客户端请求System.out.println("The message from client is:" + receiveInt);dos.writeInt(receiveInt * 18); // 返回client端dos.flush(); // 强制清空缓冲区dos.close();dis.close();is.close();}}}

简单的多客户端处理，加一个死循环即可，但如此服务器会阻塞用户的请求，即是服务器在没有处理完当前用户请求的情况下，是不能处理其他用户请求的，见改进的ModifiedServer

改进的server

package socket;import java.io.DataInputStream;import java.io.DataOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStream;import java.net.ServerSocket;import java.net.Socket;public class ModifiedServer {/* *处理客户端请求的线程类 *////////////////////////////////////////////class RequestHandler implements Runnable {  //处理客户端请求的类定义在服务器端类主体的内部private Socket socket = null;public RequestHandler(Socket s) {this.socket = s;}@Overridepublic void run() {processRequest();}private void processRequest() {try {InputStream is = socket.getInputStream();OutputStream os = socket.getOutputStream();DataInputStream dis = new DataInputStream(is);DataOutputStream dos = new DataOutputStream(os);int receiveInt = dis.readInt(); // 读取客户端请求System.out.println("The message from client" +clientCount+ "is:"+ receiveInt);dos.writeInt(receiveInt * 18); // 返回client端dos.flush(); // 强制清空缓冲区dos.close();dis.close();is.close();delay(200l);   //模拟业务处理延时clientCount--; //处理完成，减少client端的数量} catch (IOException e) {e.printStackTrace();}}private void delay(long l) {try {Thread.sleep(l);} catch (InterruptedException e) {e.printStackTrace();}}}////////////////////////////////////////////////////int clientCount = 0;   //客户端并发请求动态数目static int port = 8888;int maxClientCount = 200;public static void main(String[] args) {ModifiedServer ms = new ModifiedServer();try {ms.listenServer(port);} catch (IOException e) {e.printStackTrace();}}//服务器监听方法private void listenServer(int port) throws IOException {ServerSocket server = new ServerSocket(port);System.out.println("Server is listening port " + port);while (true) {clientCount++;if (clientCount <= maxClientCount) {Socket socket = server.accept();  //没有客户端请求到来时，系统将在此阻塞new Thread(new RequestHandler(socket));} else {System.out.println("服务器所能承受的客户端请求最大并发数已经到上限！");}}}}

虽然实现了多用户并发访问，但每次客户端访问，服务器端就要建立连接，花销较大，下篇请见用线程池实现套接字编程