Java TCP Socket编程

Java 为 TCP 协议提供了两个类:Socket 类和 ServerSocket 类。一个 Socket 实例代表了TCP 连接的一端。一个 TCP 连接(TCP connection)是一条抽象的双向信道,两端分别由 ip地址和端口号确定。在开始通信之前,要建立一个 TCP 连接,这需要先由客户端 TCP 向服务器端 TCP 发送连接请求。ServerSocket 实例则监听 TCP 连接请求,并为每个请求创建新的 Socket 实例。也就是说,服务器端要同时处理 ServerSocket 实例和 Socket 实例,而客户端只需要使用 Socket 实例。每个Socket实例会关联一个InputStream和OutputStream对象，我们通过将字节写入套接字的OutputStream来发送数据，并通过从InputStream来接收数据。

客户端向服务器端发送连接请求后，就被动地等待服务器的响应。典型的TCP客户端要经过下面三步操作：

1、创建一个Socket实例：构造函数向指定的远程主机和端口建立一个TCP连接；

2.通过套接字的I/O流与服务端通信；

3、使用Socket类的close方法关闭连接。

服务端的工作是建立一个通信终端，并被动地等待客户端的连接。典型的TCP服务端执行如下两步操作：

1、创建一个ServerSocket实例并指定本地端口，用来监听客户端在该端口发送的TCP连接请求；

2、重复执行：

1）调用ServerSocket的accept（）方法以获取客户端连接，并通过其返回值创建一个Socket实例；

2）为返回的Socket实例开启新的线程，并使用返回的Socket实例的I/O流与客户端通信；

3）通信完成后，使用Socket类的close（）方法关闭该客户端的套接字连接

3.TCP Demo

Demo1.基本的流发送示例：

服务端开启一个TCP服务器，参数为端口号

客户端启动一个TCP服务，参数为服务端的地址，发送的字符，端口号

 1 import java.net.Socket; 2 import java.net.SocketException; 3 import java.io.IOException; 4 import java.io.InputStream; 5 import java.io.OutputStream; 6  7 public class TCPClient { 8  9     public static void main(String[] args) throws IOException {10 11         if ((args.length < 2) || (args.length > 3))12 13             throw new IllegalArgumentException(14                     "Parameter(s):<Server> <Word> [<Port>]");15 16         String server = args[0]; // Server name or IP address17         /* Convert argument String to bytes using the default character encoding */18         byte[] senddata = args[1].getBytes();19         int servPort = (args.length == 3) ? Integer.parseInt(args[2]) : 7;20         /* Create socket that is connected to server onspecified port*/21         Socket socket = new Socket(server, servPort);22         System.out.PRintln("Connected to server...sending echo string");23 24         InputStream in = socket.getInputStream();25         OutputStream out = socket.getOutputStream();26         out.write(senddata); // Send the encoded string to the server27 28         int totalBytesRcvd = 0; // Total bytes received so far29         byte[] recvdata = new byte[in.available()];30         int bytesRcvd; // Bytes received in last read31         while (totalBytesRcvd < recvdata.length) {32             if ((bytesRcvd = in.read(recvdata, totalBytesRcvd, recvdata.length33                     - totalBytesRcvd)) == -1)34                 throw new SocketException("Connection closed prematurely");35             totalBytesRcvd += bytesRcvd;36         } // data array is full37 38         System.out.println("Received: " + new String(recvdata));39 40         socket.close(); // Close the socket and its streams41     }42 }

 1 import java.net.*; // for Socket, ServerSocket, andInetAddress 2 import java.io.*; // for IOException and Input/OutputStream 3  4 public class TCPServer { 5  6     private static final int BUFSIZE = 32; // Size of receivebuffer 7  8     public static void main(String[] args) throws IOException { 9 10         if (args.length != 1) // Test for correct # of args11             throw new IllegalArgumentException("Parameter(s): <Port>");12 13         int servPort = Integer.parseInt(args[0]);14 15         /* Create a server socket to accept client connection requests */16         ServerSocket servSock = new ServerSocket(servPort);17 18         int recvMsgSize; // Size of received message19         byte[] receiveBuf = new byte[BUFSIZE]; // Receive buffer20 21         while (true) { // Run forever, accepting and servicing connections22 23             Socket clntSock = servSock.accept(); // Get client connection24 25             SocketAddress clientAddress = clntSock.getRemoteSocketAddress();26 27             System.out.println("Handling client at " + clientAddress);28 29             InputStream in = clntSock.getInputStream();30             OutputStream out = clntSock.getOutputStream();31 32             /* Receive until client closes connection, indicated by -1 return*/33 34             while ((recvMsgSize = in.read(receiveBuf)) != -1) {35 36                 out.write(receiveBuf, 0, recvMsgSize);37             }38             clntSock.close(); // Close the socket. We are done with this client!39         }40         /* NOT REACHED */41 42     }43 }

Demo2.

客户端从控制台输入字符串，发送到服务端

服务端受到客户端的字符串后，加上部分信息（echo字符串）返回到客户端

 1 package zyb.org.client; 2  3 import java.io.BufferedReader; 4 import java.io.IOException; 5 import java.io.InputStreamReader; 6 import java.io.PrintStream; 7 import java.net.Socket; 8 import java.net.SocketTimeoutException; 9 10 public class Client {11     public static void main(String[] args) throws IOException {12         //客户端请求与本机在20006端口建立TCP连接 13         Socket client = new Socket("127.0.0.1", 20006);14         client.setSoTimeout(10000);15         //获取键盘输入 16         BufferedReader input = new BufferedReader(new InputStreamReader(System.in));17         //获取Socket的输出流，用来发送数据到服务端  18         PrintStream out = new PrintStream(client.getOutputStream());19         //获取Socket的输入流，用来接收从服务端发送过来的数据  20         BufferedReader buf =  new BufferedReader(new InputStreamReader(client.getInputStream()));21         boolean flag = true;22         while(flag){23             System.out.print("输入信息：");24             String str = input.readLine();25             //发送数据到服务端  26             out.println(str);27             if("bye".equals(str)){28                 flag = false;29             }else{30                 try{31                     //从服务器端接收数据有个时间限制（系统自设，也可以自己设置），超过了这个时间，便会抛出该异常32                     String echo = buf.readLine();33                     System.out.println(echo);34                 }catch(SocketTimeoutException e){35                     System.out.println("Time out, No response");36                 }37             }38         }39         input.close();40         if(client != null){41             //如果构造函数建立起了连接，则关闭套接字，如果没有建立起连接，自然不用关闭42             client.close();    //只关闭socket，其关联的输入输出流也会被关闭43         }44     }45 }

 1 package zyb.org.server; 2  3 import java.net.ServerSocket; 4 import java.net.Socket; 5  6 public class Server { 7     public static void main(String[] args) throws Exception{ 8         //服务端在20006端口监听客户端请求的TCP连接 9         ServerSocket server = new ServerSocket(20006);10         Socket client = null;11         boolean f = true;12         while(f){13             //等待客户端的连接，如果没有获取连接14             client = server.accept();15             System.out.println("与客户端连接成功！");16             //为每个客户端连接开启一个线程17             new Thread(new ServerThread(client)).start();18         }19         server.close();20     }21 }

 1 package zyb.org.server; 2  3 import java.io.BufferedReader; 4 import java.io.InputStreamReader; 5 import java.io.PrintStream; 6 import java.net.Socket; 7  8 /** 9  * 该类为多线程类，用于服务端10  */11 public class ServerThread implements Runnable {12 13     private Socket client = null;14     public ServerThread(Socket client){15         this.client = client;16     }17     18     @Override19     public void run() {20         try{21             //获取Socket的输出流，用来向客户端发送数据22             PrintStream out = new PrintStream(client.getOutputStream());23             //获取Socket的输入流，用来接收从客户端发送过来的数据24             BufferedReader buf = new BufferedReader(new InputStreamReader(client.getInputStream()));25             boolean flag =true;26             while(flag){27                 //接收从客户端发送过来的数据28                 String str =  buf.readLine();29                 if(str == null || "".equals(str)){30                     flag = false;31                 }else{32                     if("bye".equals(str)){33                         flag = false;34                     }else{35                         //将接收到的字符串前面加上echo，发送到对应的客户端36                         out.println("echo:" + str);37                     }38                 }39             }40             out.close();41             client.close();42         }catch(Exception e){43             e.printStackTrace();44         }45     }46 47 }

参考文章：

【Java TCP/IP Socket】TCP Socket（含代码）http://blog.csdn.net/ns_code/article/details/14105457

《Java TCP/IP Socket 编程》