Java socket 示例

这是一个简单的 Java socket 示例，其中一个客户端会向服务器发送消息，服务器会将消息返回给客户端：

服务器代码：

import java.io.*;
import java.net.*;

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;

        try {
            serverSocket = new ServerSocket(9999);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 9999.");
            System.exit(1);
        }

        Socket clientSocket = null;
        System.out.println("Waiting for connection.....");

        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        System.out.println("Connection successful");
        System.out.println("Waiting for input.....");

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String inputLine;

        while ((inputLine = in.readLine()) != null) {
            System.out.println("Server: " + inputLine);
            out.println(inputLine);

            if (inputLine.equals("Bye.")) {
                break;
            }
        }

        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

客户端代码：

import java.io.*;
import java.net.*;

public class Client {
    public static void main(String[] args) throws IOException {
        Socket echoSocket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            echoSocket = new Socket("localhost", 9999);
            out = new PrintWriter(echoSocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(echoSocket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        }

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;

        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);

            if (userInput.equals("Bye.")) {
                break;
            }

            System.out.println("echo: " + in.readLine());
        }

        out.close();
        in.close();
        stdIn.close();
        echoSocket.close();
    }
}

运行服务器后，运行客户端，输入一些消息，可以看到服务器会将消息返回给客户端。如果客户端输入 "Bye."，程序会退出。