Java套接字连接重置

Question

I am trying to make simple server client app that lets the client send a file to the server then the server sends acknowledgement message that it received the file

this is the server class.

public class Server {

public static void main(String[] args) {
    try {
        ServerSocket server=new ServerSocket(9090);
        while(true){
            Socket clientSocket=server.accept();
            ClientThread client=new ClientThread(clientSocket);
            client.start();
        }
    } catch (IOException e) {
        System.out.println(e.toString());
    }

}

}

ClientThread class

public class ClientThread extends Thread {

private Socket socket;// socket to connect through
private BufferedInputStream SocketInput;// stream to read from socket
private BufferedOutputStream FileOutput;// stream to write file through it
private PrintWriter SocketOutput; // print writer to write through socket

public ClientThread(Socket socket){// constructor
    this.socket=socket;
}

public void run(){
    try {
        //get socket input stream
        SocketInput=new BufferedInputStream(socket.getInputStream());

        //get socket output stream
        SocketOutput=new PrintWriter(socket.getOutputStream(),true);

        // get the file from client
        int NBytes=0;
        byte[] data=new byte[1024];

        FileOutput=new BufferedOutputStream(new   FileOutputStream("C:/Users/mohamed/Desktop/Download/band.jpg"));      
        while((NBytes=SocketInput.read(data))!=-1){
            FileOutput.write(data,0,NBytes);
            FileOutput.flush();
        }

        // send ack. that file has been received
        SocketOutput.println("File has been sent sucessfully");

        //close all streams
        FileOutput.close();
        SocketInput.close();
        SocketOutput.close();
        socket.close();

    }
    catch (IOException e) {
        System.out.println(e.toString());
    }
}
}

Client class

public class Client {

public static void main(String[] args) {

    // file will be sent
    File f=new File("D:/images/band.jpg");

    try {

        // get address of local host
        InetAddress serverAddress=InetAddress.getLocalHost();

        //create socket
        Socket socket=new Socket(serverAddress,9090);

        // create streams
        BufferedInputStream input=new BufferedInputStream(new FileInputStream(f));
        BufferedOutputStream output=new BufferedOutputStream(socket.getOutputStream());
        BufferedReader p=new BufferedReader(new InputStreamReader(socket.getInputStream()));

        // send the file
        byte[] data=new byte[1024];
        int Nbytes=0;

        while((Nbytes=input.read(data))!=-1){
            output.write(data,0,Nbytes);
            output.flush();
        }

        // read the ack. and print it
        System.out.println(p.readLine());

        //close streams & socket
        p.close();
        input.close();
        output.close();
        socket.close();

    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

what i get when i run the server and the client i got nothing , if i stop the client the server app types in the console exception connection reset , but if i remove the part of the acknowledgement the file is received and nothing goes wrong ,what is the problem?

Answer 1

You're deadlocked. The client is reading the socket to end of stream, and you haven't closed the socket, so there is no end of stream, so when you go to read the ACK line both peers are reading.

You don't need the ACK line. Just remove it. Don't send it and don't read it.

Answer 2

Because if you have connection side's code like this

    while((Nbytes=input.read(data))!=-1){
        output.write(data,0,Nbytes);
        output.flush();
    }

    // read the ack. and print it
    System.out.println(p.readLine());

You will block on the last line and wait for input. But since sockets are still open your reading side code

   while((NBytes=SocketInput.read(data))!=-1){ <-- HERE U ARE BLOCKED
        FileOutput.write(data,0,NBytes);
        FileOutput.flush();
    }

will block on while loop condition. Until connection is valid and input is not closed, #read will not return thus you got block.

Try to close output stream after all the content is transmited

    while((Nbytes=input.read(data))!=-1){ 
        output.write(data,0,Nbytes);
        output.flush();
    }
    output.close(); // this should unblock blocked thread on the other side
    // read the ack. and print it
    System.out.println(p.readLine());

This should effectively tell the other side that no other data will be transmited (blocked read method will return -1)