如何使用 Java Socket 监听客户端？

Question

我正在使用“ServerSocket”和“Socket”，我遇到的问题是：我使用 serverSocket 创建了一个服务器，我正在等待客户端连接，当它连接时我会收到一些信息，这是我的问题，我如何继续听取客户的意见并接收客户的指示？

在下面的示例中，我正在创建一个服务器，当客户端连接时，我将连接保存在“clientSocket”中。

@GET
@Path("/createServer")
public String conect() throws IOException { 
    
    serverSocket = new ServerSocket(3242);      
    clientSocket = serverSocket.accept();
    ...
    ...
  }

从这一点开始我需要一直监听这个clientSocket，当客户端发送一些我需要捕获的信息来执行一些动作时，该怎么做？

Answer 1

ServerSocket.accept() 给你一个java.net.Socket。文档here

从那里开始，您可以使用其输入流 (Socket.getInputStream()) 读取该套接字或写入其输出流 (Socket.getOutputStream())

您的套接字（客户端和服务器）将一直存在，直到它们被 closed 或垃圾收集为止，因此请记住，只要您需要它们，就对每个套接字进行强引用。

示例程序（简单的回显服务器。在客户端输入bye 退出）：

Server.java

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
import java.util.Scanner;

public class Server {

  private static volatile boolean stopped = false;

  public static void main(String[] args) throws IOException, InterruptedException {

    try (ServerSocket server = new ServerSocket(3001)) {
      System.out.println("Server ready to accept connections on port " + server.getLocalPort());

      final Socket client = server.accept();
      System.out.println("Client connected using remote port " + client.getPort());

      final Thread t = new Thread(() -> {
        try {
          try (InputStream clientIn = client.getInputStream()) {
            try (OutputStream clientOut = client.getOutputStream()) {
              echo(clientIn, clientOut);
            }
          }
        } catch (IOException ioe) {
          ioe.printStackTrace();
          stopped = true;
        }
      });
      t.setDaemon(true);
      t.start();

      while (!stopped) {
        Thread.sleep(10);
      }
      System.out.println("Program exit");

    }

  }

  private static void echo(InputStream clientIn, OutputStream clientOut) throws IOException {
    
    try (Scanner clientScan = new Scanner(clientIn, StandardCharsets.UTF_8)) {
      try (OutputStreamWriter clientWriter = new OutputStreamWriter(clientOut, StandardCharsets.UTF_8)) {
        
        while (!stopped) {
          final String fromClient = clientScan.nextLine();
          System.out.println("In: " + fromClient);
          clientWriter.write(fromClient);
          clientWriter.write(System.lineSeparator());
          clientWriter.flush();
          if ("bye".equalsIgnoreCase(fromClient.trim())) {
            stopped = true;
          }
        }
        System.out.println("Loop done");
        
      }
    }
    
  }

}

Client.java

import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.Scanner;

public class Client {
  private static volatile boolean stopped = false;

  public static void main(String[] args) throws UnknownHostException, IOException {
    System.out.println("Client launched");
    try (Socket client = new Socket("localhost", 3001)) {
      System.out.println("Connected on remote port " + client.getPort() + " from " + client.getLocalPort());

      try (Scanner console = new Scanner(System.in)) {
        try (OutputStreamWriter toServer = new OutputStreamWriter(client.getOutputStream())) {

          final Thread t = new Thread(() -> printEverything(client));
          t.setDaemon(true);
          t.start();

          while (!stopped) {
            final String fromConsole = console.nextLine();
            if (stopped)
              break;
            toServer.write(fromConsole);
            toServer.write(System.lineSeparator());
            toServer.flush();
          }

        }
      }

    }
    System.out.println("Program exit");

  }

  private static void printEverything(Socket client) {
    try (Scanner server = new Scanner(client.getInputStream())) {
      while (!stopped) {
        final String fromServer = server.nextLine();
        System.out.println("Server said: " + fromServer);
        if ("bye".equalsIgnoreCase(fromServer.trim())) {
          stopped = true;
        }
      }
      System.out.println("Loop done. Press enter to exit");
    } catch (IOException e) {
      e.printStackTrace();
      stopped = true;
    }
  }

}