Java 简单客户端-服务器应用程序-套接字问题

我正在使用TCP套接字编写一个简单的客户机-服务器应用程序。它使用多线程原理，允许多个客户端连接到同一台服务器

我在找出套接字中的一些错误时遇到了一些困难，您可能会告诉我，我在这个环境中是相当新的

我将向您展示我拥有的代码以及从中获得的输出，但基本上问题在于客户机与服务器的连接，我浏览了所有代码，但仍然找不到问题所在

服务器：

public static ArrayList<String> userList = new ArrayList<String>();
public static int index;
public static String date;
public static void main(String args[]) throws Exception {//inicio main      


    ServerSocket server = new ServerSocket(6500);   //Create socket on port 6500
    System.out.println ("Server started on port 6500");     
    while (true){   //Waiting for clients
        System.out.println("Server waiting for client connections..");
        Socket socket = null;
        BufferedReader reader = new BufferedReader(new FileReader("C:\\UNIV\\Redes\\workspace\\Copy of Ex_4.3_Teste\\lists\\blacklist.txt"));
        String line = null;
        socket = server.accept();

        // Blacklist verification
        while ((line = reader.readLine()) != null) {
            if (line.equals(socket.getInetAddress().toString())) {
                System.out.println("IP Blacklisted: " + socket.getInetAddress().toString());
                System.out.println("Closing connection to " + socket.getInetAddress().toString());
                PrintStream checkBlack = new PrintStream(socket.getOutputStream(),true);
                checkBlack.println("***BLACKLISTED***");
                reader.close();
                checkBlack.close();
                socket.close();
                break; 
            }
        }//End of Blacklist Verification

        //Sending feedback in case of approved client
        try { 
        PrintStream checkBlack = new PrintStream(socket.getOutputStream(),true);
        checkBlack.println("***NBLACKLISTED***");
        checkBlack.close();
        } catch (SocketException e) {

        }
        userList.add(socket.getInetAddress().toString()); //Add connected user's IP to USERLIST
        System.out.println("New connection..");
        System.out.println("Size of UserList: " + userList.size());
        Thread t = new Thread(new EchoClientThread(socket)); 

        t.start(); //Starting Client Thread


    }//End of Waiting for Clients       
}//End of Main  

public static class EchoClientThread implements Runnable{
    private Socket s;
    public EchoClientThread(Socket socket) {
        this.s = socket;
    }
    public void run() { 
        String threadName = Thread.currentThread().getName();   //Thread Name
        String stringClient = s.getInetAddress().toString();    //Client IP
        System.out.println("Connected to " + stringClient); 

        try{                
            BufferedReader input = new BufferedReader(
                    new InputStreamReader(s.getInputStream()));         
            PrintStream output = new PrintStream(
                    s.getOutputStream(),true);
            String line;
            while ((line = input.readLine()) !=null) {  //Input Cycle   

                System.out.println (stringClient+": "+threadName+": "+line);    //Print command from client

                if (line.equalsIgnoreCase("9")){ //Exit
                    break;
                }

                else if (line.equalsIgnoreCase("1")){   //Send List of Online Users
                    System.out.println("Option 1: Sending list of online users to " + stringClient);
                    output.println(" ");
                    output.println("List of Online Users:");
                    output.println(" ");
                    for(int i=0;i<userList.size();i++){
                        output.println(userList.get(i));
                    }
                }

                else if (line.equalsIgnoreCase("2")) {  //Send message to a single user
                    System.out.println("Nothing here yet..");
                }

                else if (line.equalsIgnoreCase("3")) {  //Send message to all the online users
                    System.out.println("Nothing here yet..");
                }

                else if (line.equalsIgnoreCase("4")){   //Send User Blacklist
                    System.out.println("Option 4: Sending user blacklist to " + stringClient);
                    BufferedReader reader = new BufferedReader(new FileReader("C:\\UNIV\\Redes\\workspace\\Copy of Ex_4.3_Teste\\lists\\blacklist.txt"));
                    String lineRead = null;
                    output.println(" ");
                    output.println("User Blacklist:");
                    output.println(" ");
                    while ((lineRead = reader.readLine()) != null) {
                        output.println(lineRead);
                    }
                    reader.close();
                }

                else{
                    output.println("Unknown command.");
                }   

                output.println("***CLOSE***");  //Closes client's input cycle
                output.println("***NBLACKLISTED***");   //Sending feedback in case of approved client                       
            }//Input Cycle End

            output.println("See you later!"); 
            input.close();  //Closes inputStream 
            output.close(); //Closes outputStream
            s.close();  //Closes Socket                         
        }
        catch (Exception e){
            System.err.println("Server Side Error!");
            System.out.println(e);
        }
        userList.remove(s.getInetAddress().toString());
        System.out.println("Client "+ stringClient+" was disconnected!");                   
    }//End of run()  
}//End of EchoClientThread
}//End of EchoServerThread

但只要我尝试与客户联系，就会发生以下情况：

服务器端：

Server started on port 6500
Server waiting for client connections..
New connection..
Size of UserList: 1
Server waiting for client connections..
Connected to /127.0.0.1
java.net.SocketException: Socket is closed
Server Side Error!
Client /127.0.0.1 was disconnected!

但在客户端，它仍然显示输入菜单和命令提示符，如下所示：

CLIENT MENU

1 - List on-line users
2 - Send message to a single user
3 - Send message to all on-line users
4 - List Blacklisted Users
9 - Exit

127.0.0.1:6500#>

当我在客户端提示符上输入内容时，我得到：

127.0.0.1:6500#>1
Client Side Error!
java.net.SocketException: Software caused connection abort: recv failed
Connection Terminated

我知道错误的意思，

套接字关闭了

几乎是不言自明的，但我就是找不到导致套接字关闭的代码问题

---

非常感谢您的帮助。

您的黑名单机制不太正确

当您关闭与套接字关联的流时，它也将关闭套接字

所以服务器关闭它获得的任何套接字，然后将其交给线程， 尝试使用套接字但失败

    // Blacklist verification
    while ((line = reader.readLine()) != null) {
        // blah blah blah
    }//End of Blacklist Verification

    //Sending feedback in case of approved client
    try { 
        PrintStream checkBlack = new PrintStream(socket.getOutputStream(),true);
        checkBlack.println("***NBLACKLISTED***");
        checkBlack.close();  // <== why are you closing the stream?
    } catch (SocketException e) {

    }

---

调试器是你的朋友。

你试过调试服务器代码吗？在我看来，您的服务器只是因为异常而关闭了套接字。如果您也可以发布异常，那么我得到的唯一异常是

java.net.SocketException:Socket在客户端尝试连接到服务器时关闭。但调试并没有帮到我，这也是我在这里问这个问题的部分原因。显然，它在
System.out.println（“连接到”+stringClient）
之后立即关闭套接字，但我不知道为什么。我想我需要关闭流，以便为命令输入打开一个新的流。好吧，我想那不是。每天都是学习日^^非常感谢。PrintStream将SocketStream包裹起来，这样您就可以挂起它了。除非希望基础流关闭，否则不要关闭。流可能会变得混乱，有些你必须关闭其他你必须离开的流。哦，我明白了，执行
socket.getOutputStream（）.write（）
只写它必须写入的内容，然后关闭流而不关闭套接字？不，流保持打开状态。创建套接字时，您将创建一个上游（out）和一个下游（in）。每个插座只能有一个，因此它们需要在插座的使用寿命内保持打开状态。当您需要发送或接收某些内容时，您只需获得适当的流并进行读写。无论何时在套接字上调用get***Stream，您都会得到***的相同流，如果有多个线程使用同一套接字，这一点很重要。当套接字关闭时，流将为您清理。这有点令人困惑，但我想我现在明白了，感谢您花时间：）
127.0.0.1:6500#>1
Client Side Error!
java.net.SocketException: Software caused connection abort: recv failed
Connection Terminated

    // Blacklist verification
    while ((line = reader.readLine()) != null) {
        // blah blah blah
    }//End of Blacklist Verification

    //Sending feedback in case of approved client
    try { 
        PrintStream checkBlack = new PrintStream(socket.getOutputStream(),true);
        checkBlack.println("***NBLACKLISTED***");
        checkBlack.close();  // <== why are you closing the stream?
    } catch (SocketException e) {

    }

    // Blacklist verification
    while ((line = reader.readLine()) != null) {
        // blah blah blah
    }//End of Blacklist Verification

    //Sending feedback in case of approved client
    try { 
        socket.getOutputStream().write("***NBLACKLISTED***\n".getBytes());
    } catch (SocketException e) {
        e.printStackTrace();
    }