如何在Java中制作服务器和客户端？

Question

I i am making a server/client but there seems to be a problem. I cannot seem to connect when i click the button.Please help.Not sure what i did wrong.Feel free to edit code to fix it then comment please.I have a connect button,and a send button. I think it has something to do with the highlighted code but it could be anything. I know this isnt very specific but basically heres the code and it doesnt work. I cant connect . please help!

Client

public class chat_client extends javax.swing.JFrame {


    String username;
    Socket sock;
    BufferedReader reader;
    PrintWriter writer;
    ArrayList<String>userList = new ArrayList();
    Boolean isConnected = false;



    public chat_client() {
        initComponents();
        getContentPane().setBackground(Color.white);
        this.setIconImage(new ImageIcon(getClass()
                .getResource("dogeIcon.jpg")).getImage());
        this.setLocationRelativeTo(null);
    }

    public class IncomingReader implements Runnable{

        public void run(){
            String stream;
            String[] data;
            String done = "Done", connect = "Connect", 
                    disconnect = "Disconnect", chat = "Chat";

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

                    data = stream.split("^");

                    if (data[2].equals(chat)){
                        txtChat.append(data[0] + ":" + data[1] + "\n");

                    } else if (data[2].equals(connect)){
                        txtChat.removeAll();
                        userAdd(data[0]);

                    } else if (data[2].equals(disconnect)){
                        userRemove(data[0]);

                    } else if (data[2].equals(done)){
                        userList.setText("");
                        writeUsers();

                    }

            } catch(Exception ex){
            }
        }
    }

    public void ListenThread(){
        Thread IncomingReader = new Thread(new IncomingReader());
        IncomingReader.start();
    }

    public void userAdd(String data){
        userList.add(data);
    }

    public void userRemove(String data){
        txtChat.append(data + " has disconnected \n");
    }

    public void writeUsers(){
        String[] tempList = new String[(userList.size())];
        userList.toArray(tempList);
        for (String token:tempList){
            userList.append(token + "\n");
        }
    }

    public void sendDisconnect(){
        String bye = (username + "^ ^Disconnected");
        try{
            writer.println(bye);
            writer.flush();

        } catch(Exception e){
            txtChat.append("Could Not Send Disconnect Message \n");
        }
    }

    public void Disconnect(){
        try{
            txtChat.append("Disconnected\n");
            sock.close();
        } catch(Exception ex){
            txtChat.append("Failed to disconnect\n");
        }
        isConnected = false;
        txtUser.setEditable(true);
        userList.setText("");
    }

(This is the highlighted part where i think the problem is)

 ***private void connectActionPerformed(java.awt.event.ActionEvent evt) {  
     if (isConnected == false){
        username = txtUser.getText();
        txtUser.setEditable(false);

        try{
            sock = new Socket("localhost", 1023);
            InputStreamReader streamreader 
                    = new InputStreamReader(sock.getInputStream());
            reader = new BufferedReader(streamreader);
            writer = new PrintWriter(sock.getOutputStream());
            writer.println(username + "^has connected.^Connect");
            writer.flush();
            isConnected = true;


        } catch(Exception ex){
            txtChat.append("Cannot Connect! Try Again\n");
            txtUser.setEditable(true);
        }
        ListenThread();
    } else if (isConnected == true){
        txtChat.append("You is connected bra\n");
    } 
}***               

(Ends here-the problem/highlighted part)

private void btn_SendActionPerformed(java.awt.event.ActionEvent evt) {     

    String nothing = ""; 
    if ((txtMsg.getText()).equals(nothing)){

       txtMsg.setText("");

       txtMsg.requestFocus();

    } else {
        try{
            writer.println(username + "^" + txtMsg.getText() + "^" 
                    + "Chat");
            writer.flush();
        } catch (Exception ex){
            txtChat.append("Message was not sent\n");
        }
        txtMsg.setText("");
        txtMsg.requestFocus();

    }

Answer 1

A couple things:

1. You're getting a java.net.ConnectionException (see below) because the connection is being refused. This could be because the server you are trying to connect to is not running, the server is not accepting client connections, the server is not accessible by the client, or you are connecting to the wrong port number.

2. It is generally bad coding practice to catch Exception directly. You want to either catch the most specific exception that ranges across the variety of exceptions that can be thrown (in this case, IOException ) or catch each possible one individually, which is the preferred method. Catch the most specific exceptions before the more general ones so that they are not masked by them. Furthermore it is a good idea to use the Throwable class's getMessage() method so that you can figure out the reason for the exception being thrown. For example:

    } catch (java.net.ConnectException ex) { System.err.println("ConnectException: " + ex.getMessage()); // May return "Connection refused", "Connection timed out", "Connection reset", etc. } catch (java.rmi.UnknownHostException ex) { System.err.println("UnknownHostException: " + ex.getMessage()); // Returns the name of the host you were attempting to connect to } catch (...) { // code here } catch (java.io.IOException ex) { System.err.println("IOException: " + ex.getMessage()); // May return a problem with the BufferedReader or InputStreamReader or PrintWriter } 

   Of course, the statements in the catch clause can be modified to your liking.