Java - 通过套接字发送文件（聊天客户端 - >服务器 - >另一个聊天客户端）

Question

So I'm working on a chat program and now I want to add a send file option. I tried adding it and it worked but right after the file transfer finishes, both of the sockets close(the sockets of the two clients). Here is an SSCCE for the Chat client:

public class SSCCEChatClient extends JFrame {

    private JPanel contentPane;
    private JTextField inputUsernameField;
    private JTextArea textArea;
    String serversock = "84.252.37.82";
    String username;
    Socket sock;
    BufferedReader reader;
    PrintWriter writer;
    InputStreamReader streamreader;

    public class IncomingReader implements Runnable{

        public void run() {
            String stream;
            String[] data;

            try {
                while ((stream = reader.readLine()) != null) {

                    data = stream.split("`");
                     if(data[2].equals("receiveFile")&&(!data[3].equals(username))){
                        DataInputStream in = new DataInputStream(sock.getInputStream());
                        byte[] bytes = new byte[Integer.parseInt(data[1])];
                        in.read(bytes);
                        FileOutputStream fos = new FileOutputStream(System.getProperty("user.home") + "\\Desktop\\" + data[0]);
                        fos.write(bytes);
                        fos.close();
                        in.close();
                        textArea.append("Success!");
                    }else if(data[2].equals("server")){
                        textArea.append(data[0]);
                    }

                }
           }catch(Exception ex) {
           }
        }
    }//Incoming Reader

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    SSCCEChatClient frame = new SSCCEChatClient();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public SSCCEChatClient() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);

        textArea = new JTextArea();
        contentPane.add(textArea, BorderLayout.SOUTH);

        JButton btnNewButton = new JButton("Send File");
        btnNewButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                File transferFile = new File (System.getProperty("user.home") + "\\Desktop\\PNG\\Night.png");
                byte [] bytearray  = new byte [(int)transferFile.length()];
                try {
                    BufferedInputStream bin = new BufferedInputStream(new FileInputStream(transferFile));
                    bin.read(bytearray,0,bytearray.length);
                    DataOutputStream os = new DataOutputStream(sock.getOutputStream());
                    writer.println(transferFile.getName() + "`" + transferFile.length() + "`receiveFile`" + username);
                    writer.flush();
                    os.write(bytearray,0,bytearray.length);
                    os.flush();
                    bin.close();
                    os.close();

                } catch (IOException e) {
                    e.printStackTrace();
                }
                System.out.println("File transfer complete");
            }
        });
        contentPane.add(btnNewButton, BorderLayout.CENTER);

        JButton btnNewButton_1 = new JButton("Connect");
        btnNewButton_1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                try {
                    username = inputUsernameField.getText();
                    sock = new Socket(serversock, 5000);
                    streamreader = new InputStreamReader(sock.getInputStream());
                    reader = new BufferedReader(streamreader);
                    writer = new PrintWriter(sock.getOutputStream());
                    Thread IncomingReader = new Thread(new IncomingReader());
                    IncomingReader.start();
                    writer.println(username + "``connect");
                    writer.flush();

                } catch (Exception ex) {
                    textArea.append("\nCannot Connect!");
                }
            }
        });
        contentPane.add(btnNewButton_1, BorderLayout.WEST);

        inputUsernameField = new JTextField();
        contentPane.add(inputUsernameField, BorderLayout.NORTH);
        inputUsernameField.setColumns(10);
    }

}

and here is the Server side:

public class SSCCEServer {
    static ArrayList<PrintWriter> clientOutputStreams;
    static ArrayList<DataOutputStream> clientDataOutputStreams;
    static ArrayList<String> onlineUsers = new ArrayList<>();
    public class ClientHandler implements Runnable  {
        BufferedReader reader;
        Socket sock;
        PrintWriter client;


        public ClientHandler(Socket clientSocket, PrintWriter user) {
        // new inputStreamReader and then add it to a BufferedReader
            client = user;
            try {
                sock = clientSocket;
                System.out.println(clientSocket.getRemoteSocketAddress().toString() + " - ");
                InputStreamReader isReader = new InputStreamReader(sock.getInputStream());
                reader = new BufferedReader(isReader);
            }
            catch (Exception ex) {
                System.out.println("error beginning StreamReader");
            }

        }

        public void run() {
            String message;
            String[] data;
            try {
                while ((message = reader.readLine()) != null) {

                    data = message.split("`");

                    if(data[2].equals("receiveFile")){
                        DataInputStream in = new DataInputStream(sock.getInputStream());
                        byte[] bytes = new byte[Integer.parseInt(data[1])];
                        in.read(bytes);
                        tellEveryone(data[0] + "`" + data[1] + "`" + data[2] + "`" + data[3]);
                        for(DataOutputStream dos:clientDataOutputStreams){
                            try {
                                dos.write(bytes);
                                dos.close();
                            }
                            catch (Exception ex) {
                                System.out.println("error telling everyone");
                            }
                        }
                        tellEveryone("File transfer complete``server");
                    }else if(data[2].equals("connect")){
                        System.out.println(data[0] + "has connected.");
                    }else {
                        System.out.println("No Conditions were met.");
                      }
                 }
            }
            catch (Exception ex) {
                System.out.println("lost a connection");
                System.out.println(ex.getMessage().toString());
                clientOutputStreams.remove(client);
            }
        }
    }
    public void tellEveryone(String message) {
    // sends message to everyone connected to server
        for(PrintWriter writer:clientOutputStreams){
                try {
                    writer.println(message);
                    //pop("Sending: " + message);
                    writer.flush();
                }
                catch (Exception ex) {
                    System.out.println("error telling everyone");
                }
        }
       }
    public static void main(String[] args) {
        new SSCCEServer().go();
    }
    public void go(){
        clientOutputStreams = new ArrayList<PrintWriter>();
        clientDataOutputStreams = new ArrayList<>();

        try {
            @SuppressWarnings("resource")
            ServerSocket serverSock = new ServerSocket(5000);
            while(true){
                Socket clientSock = serverSock.accept();
                PrintWriter writer = new PrintWriter(clientSock.getOutputStream());
                clientOutputStreams.add(writer);
                clientDataOutputStreams.add(new DataOutputStream(clientSock.getOutputStream()));
                Thread listener = new Thread(new ClientHandler(clientSock, writer));
                listener.start();
            }
        } 
        catch (Exception ex)
        {
            System.out.println("error making a connection");
        }
    }

}

Sorry if it's really long but this is the minimal amount I could bring it to. Also it's not the whole thing because it misses the send text method but that doesn't affect the SSCCE. I've demonstrated the send method with the method 'tellEveryone' from the server side. Also, the "\\PNG\\Night.png" is just an example, you can make your own folder and file in order to run the SSCCE. What can I do to fix the closing of the socket after the file is send?

Answer 1

1. close all Objects in finally block ( try - catch - finally )

2. you have got issue with Concurency in Swing , but there are three ways

   a) proper ways

   • wrap code to the Runnable#Thread (easiest), have to wrap any changes to the Swing GUI into invokeLater()

   • use SwingWorker (implemented in standard ways), where methods publish , process and done quite guarante that all events are done on EDT

   b) shortcuts, works but not proper of ways

   • wrap Swing GUI code into invokeLater() directly

Answer 2

The socket closes when you close the output stream. If you want to keep the socket open, do not close the stream. For reference have a look at SocketOutputStream.java