Getting "Error: java.net.SocketException: Socket is closed" when trying to send a message from my Client class to my Server class

Question

我不明白为什么。当服务器向客户端发送一个字符串时，客户端就可以正常接收它。但是当我向我的客户端 class 添加代码以将字符串发送到我的服务器时，它不起作用。帮忙？

编辑：所以我删除了 out.close();在我的服务器 class 中替换为 skt.shutdownOutput();但现在当我打电话给 classes 时，我得到：

======================
Server has connected!
Server: Sending message: Test string to show connection between server and client.
Client: Received message: null
Server: Received message: null

为什么？

客户Class：

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

class Client {

public static void main(String args[]) {

}

//for receiving messages from Server

public void receiveMessage() {
    try {
        Socket skt = new Socket(InetAddress.getLocalHost().getHostName(), 1234);
        BufferedReader in = new BufferedReader(new InputStreamReader(skt.getInputStream()));
        //while (!in.ready()) {}
        System.out.println("Client: Received message: " + in.readLine()); // Read one line and output it
        in.close();
        //skt.close(); //maybe delete
    } catch (Exception e) {
        System.out.print("Client had error receiving message.\n");
    }
}

//for sending messages to Server
public void sendMessage(String message) throws IOException {
    try {
        Socket skt = new Socket(InetAddress.getLocalHost().getHostName(), 1234);
        PrintWriter pw = new PrintWriter(skt.getOutputStream());
        System.out.println("Client: Sending message: " + message);
        pw.print(message);
        //skt.close(); //maybe delete
    } catch (Exception e) {
        System.out.println(e);
        System.out.print("Client had error sending message.\n");
    }

}
}

服务器Class:

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.concurrent.*;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Server {

String message = "Test string to show connection between server and client.";

public void Open() {
    final ExecutorService clientProcessingPool = Executors.newFixedThreadPool(10);
    Runnable serverTask = new Runnable() {

        @Override
        public void run() {
            try {
                System.out.println("Opening...");
                ServerSocket srvr = new ServerSocket(1234);
                while (true) {
                    Socket skt = srvr.accept();
                    clientProcessingPool.submit(new ClientTask(skt));
                }
            } catch (Exception e) {
                System.out.println(e);
                System.out.print("You're opening too many servers in the same location, fool!\n");
            }
        }
    };
    Thread serverThread = new Thread(serverTask);
    serverThread.start();
}

private class ClientTask implements Runnable {

    private final Socket skt;

    private ClientTask(Socket skt) {
        this.skt = skt;
    }

    @Override
    public void run() {
        //for sending messages
        System.out.println("======================");
        System.out.println("Server has connected!");
        PrintWriter out = null;
        try {
            out = new PrintWriter(skt.getOutputStream(), true);
        } catch (IOException ex) {
            System.out.println(ex);
            System.out.println("Server had error sending message.");
        }
        System.out.print("Server: Sending message: " + message + "\n");
        out.print(message);
        //out.close();
        try {
            skt.shutdownOutput();
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }

        /*
        try {
            skt.close();
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }*/

        //for receiving messages
        //maybe make message procesing method
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            System.out.println("Server: Received message: " + br.readLine()); // Read one line and output it
            //br.close();
            //skt.close(); //maybe delete
        } catch (Exception e) {
            System.out.println("Server had error receiving message.");
            System.out.println("Error: " + e);
        }

    }
}

}

感谢您的任何建议。

Answer 1

    out.print(message);
    out.close();

通过关闭您的 PrintStream，您将关闭基础 OutputStream。

Socket 中 getOutputStream() 的文档说：

Closing the returned OutputStream will close the associated socket.

因此，当您关闭 PrintStream 时，您也关闭了套接字。仅当您完成当前会话的客户端和服务器之间的所有通信时才关闭您的流。

您遇到的下一个问题（在您编辑之后）是您没有刷新数据。您的客户端连接，服务器打印，没有刷新，因此数据仍在缓冲区中等待，而不是在流中。像以前那样关闭流也会刷新数据，但现在您只是丢弃流，未刷新的数据将被丢弃。

因此，流关闭，客户端看到指示流结束的 null。

因此您需要在丢弃流之前刷新数据。

并且服务器报告它已收到 null，因为它的输入流上没有向它发送任何内容。客户端收到信息然后退出，这导致套接字关闭，流关闭，服务器看到流结束。

如果您调用 sendMessage 方法，您会看到几乎相同的结果。流正在写一些东西，但没有人在听它。因为消息很短，服务器不会阻止写入它，但另一端没有人在读它，它有可能被阻止。然后，服务器尝试读取发送给它的内容。但是您的客户端在完成执行并关闭套接字之前不会刷新数据。因此，服务器也会看到 null.

Getting "Error: java.net.SocketException: Socket is closed" when trying to send a message from my Client class to my Server class

Getting "Error: java.net.SocketException: Socket is closed" when trying to send a message from my Client class to my Server class

java

sockets

client

server