【Java】Javasocket通信使用read,readline函数的阻塞问题

Socket通信是Java⽹络编程中⽐较基础的部分，其原理其实就是源ip，源端⼝和⽬的ip，⽬的端⼝组成的套接字通信。其底层还设及到了TCP协议的通信。

Java中的Socket通信可以通过客户端的Socket与服务端的ServerSocket通信，同时利⽤IO流传递数据，也就是说Socket通信是⾯向流的使⽤的是BIO，并不同于后来的NIO通信⾯向缓冲。Socket通信中使⽤的IO流的read，readline等函数都是阻塞的，这就导致了在通信过程中，双⽅不能确定什么时侯是流的结束，针对这种可以通过约定结束符的⽅式进⾏结束，也可以约定⼀次传输的字节流的长度。下⾯通过代码进⾏说明

客户端

建⽴客户端线程，在run⽅法中不断对服务端进⾏发送消息，模拟多个客户端的通信，通过写⼊换⾏符，表明这次通信的结束。

1 class Client implements Runnable { 2

3 private byte[] targetIp; 4 private int port; 5

6 Client(byte[] ip, int port) { 7 this.targetIp = ip; 8 this.port = port; 9 }10

11 @Override

12 public void run() {13 try {

14 InetAddress inetAddress = InetAddress.getByAddress(targetIp);15 Socket socket = new Socket(inetAddress, port);16 System.out.println(\"client\");

17 BufferedReader socketInput = new BufferedReader(new InputStreamReader(socket.getInputStream()));18 BufferedWriter socketOutput = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));19

20 int i = 0;

21 String NAME = \"Client\";22 while (true) {

23 socketOutput.write(\"This msg from \" + NAME + \" msg id is \" + i);24 socketOutput.write(\"\\n\");//约定结束符表⽰流的结束25 i++;

26 socketOutput.flush();

27 System.out.println(\"here\");28 String str = null;

29 if (!(str = socketInput.readLine()).equals(\"\\n\")) {30 System.out.println(str);31 }32

33 }34

35 /*socket.shutdownInput();36 socket.shutdownOutput();*/37 } catch (IOException e) {38 e.printStackTrace();39 }40 41 }42 }

服务端

服务端通过accept接受客户端的连接，这个操作是阻塞的，直到有客户端的连接才能进⾏下⼀步。

1 class Server implements Runnable { 2

3 private int port; 4

5 Server(int port) { 6 this.port = port; 7 }

8 @Override

9 public void run() {10 try {

11 ServerSocket serverSocket = new ServerSocket(port);12

13 InetAddress inetAddress = serverSocket.getInetAddress();14 System.out.println(\"server\" + inetAddress.getHostAddress());15 Socket socket = serverSocket.accept();

16 BufferedReader socketInput = new BufferedReader(new InputStreamReader(socket.getInputStream()));17 BufferedWriter socketOutput = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));

18

19 int i = 0;20 while (true) {

21 String str = null;

22 if (!(str = socketInput.readLine()).equals(\"\\n\")) System.out.println(str);23 System.out.println(\"server\");24

25 String NAME = \"Server\";

26 socketOutput.write(\"This msg from \" + NAME + \" msg num is \" + i + \" reply to \" + str);27 socketOutput.write(\"\\n\");28 i++;

29 socketOutput.flush();30 }31

32 // socket.shutdownInput();33 // socket.shutdownOutput();34 } catch (IOException e) {35 e.printStackTrace();36 }37 38 }39 }

测试

1 public class SocketTest {

2 public static void main(String[] args) { 3 byte[] ip = {127, 0, 0, 1}; 4 int port = 27149;

5 Thread server = new Thread(new Server(port), \"server\"); 6 server.start();

7 Thread client = new Thread(new Client(new byte[]{0,0,0,0}, 27149)); 8 client.start(); 9 }10 }

结果

服务端针对客户端的每条信息都能够进⾏读取并返回消息给客户端，但是如果注释掉写⼊换⾏符，并判断读取是否是换⾏符的代码，就⽆法读取到流的结束。