java - 将套接字输出发送到 GUI 时出现问题

Question

我编写了这个简单的多线程聊天室，我试图将客户端/服务器输出发送到 GUI 以将其显示在聊天室文本区域中，但我在以下行得到空指针异常:

output.write(line + "\n");

这是 GUI 的完整代码:

import java.awt.*;
import javax.swing.*;
import javax.swing.JTextField;
import javax.swing.JFrame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.io.IOException;
import javax.swing.JButton; 
import java.io.Writer;


public class GUI {

    private JFrame frame;
    private JButton btnSend, btnConnect;
    private JTextArea txtChat;
    private JTextField fldText, fldName;
    private JList clientList;
    private DefaultListModel listModel;
    private JScrollPane sc, scClients;
    private JPanel jpS2All, jpS2Client, jpS2Text;
    private String Name;
    private JLabel lblErr;
    private Writer output;

    public GUI(String Name, Writer output) {
        this.Name = Name;
        this.output = output;
    }

    public GUI() {

    }


    class handler implements ActionListener, MouseListener {

        handler(String Name) {

        }

        handler() {

        }

        @Override
        public void actionPerformed(ActionEvent e) {


            clients();                 //it seems this line made the error because it creates the 
            listModel.addElement(Name);//gui and sends the output to textSend actionlistener
                                       //to display it in gui
                                       //while the output is empty, right?  
                                       //is there any way to handle this?

        }

        @Override
        public void mouseClicked(MouseEvent e) {
            fldName.setText("");
        }

        @Override
        public void mousePressed(MouseEvent e) {
        }

        @Override
        public void mouseReleased(MouseEvent e) {
        }

        @Override
        public void mouseEntered(MouseEvent e) {
        }

        @Override
        public void mouseExited(MouseEvent e) {
        }

    } //end of handler

    class textSend implements ActionListener {

        textSend(String Name, Writer output) {

        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String line = fldText.getText();
            try {
                output.write(line + "\n");             // the null exception error shows the
                output.flush();                        // error source at this line!
            } catch (IOException ioe) {
                txtChat.append("Other party hung up!");
            }
            String contenet = Name + ":" + output;
            txtChat.append(contenet);
            fldText.setText("");
        }

    }//end of textSend

    public void creatServer() {

        frame = new JFrame("enter");
        frame.setBounds(50, 50, 300, 200);
        btnConnect = new JButton("connect");
        lblErr = new JLabel();
        lblErr.setText("");
        frame.add(btnConnect, BorderLayout.EAST);
        fldName = new JTextField();
        fldName.setText("enter your name");
        fldName.addMouseListener(new handler());

        btnConnect.addActionListener(new handler(getName()));

        frame.add(fldName, BorderLayout.CENTER);
        frame.setVisible(true);

    }


    public void clients() {    //to create the chatroom GUI
        frame = new JFrame("friends");
        frame.setBounds(100, 100, 400, 400);
        jpS2All = new JPanel();
        txtChat = new JTextArea();
        txtChat.setRows(25);
        txtChat.setColumns(25);
        txtChat.setEditable(false);

        sc = new JScrollPane(txtChat);
        jpS2All.add(sc);
        frame.add(jpS2All, BorderLayout.WEST);
        jpS2Text = new JPanel();

        ////////////////////////
        fldText = new JTextField();
        fldText.setColumns(34);
        fldText.setHorizontalAlignment(JTextField.RIGHT);
        fldText.addActionListener(new textSend(getName(), output));
        jpS2Text.add(fldText);
        frame.add(jpS2Text, BorderLayout.SOUTH);

        /////////
        jpS2Client = new JPanel();

        listModel = new DefaultListModel();
        clientList = new JList(listModel);
        clientList.setFixedCellHeight(14);
        clientList.setFixedCellWidth(100);
        scClients = new JScrollPane(clientList);

        frame.add(jpS2Client.add(scClients), BorderLayout.EAST);
        /////////
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.pack();

    }//end of clients

    public String getName() {
        Name = fldName.getText();
        return Name;
    }

    public void appendText(final String message) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                txtChat.append(message);
            }
        });
    }
}

服务器代码:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

public class server {

    public void start() throws IOException {
        ServerSocket serverSocket = new ServerSocket(1234);
        while (true) {
            Socket socket = serverSocket.accept();
            ClientThread t = new ClientThread(socket);
            t.start();
        }
    }

    public static void main(String[] args) throws IOException {
        server server = new server();
        server.start();

    }

    class ClientThread extends Thread {

        Socket socket;
        InputStream sInput;
        OutputStream sOutput;
        GUI gui = new GUI();
        String Name;

        ClientThread(Socket socket) {
            this.socket = socket;

        }

        @Override
        public void run() {
            try {
                BufferedReader sInput
                        = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                Writer sOutput = new OutputStreamWriter(socket.getOutputStream());
                Name = gui.getName();
                gui = new GUI(Name, sOutput);

                try {
                    String line;
                    while ((line = sInput.readLine()) != null) {
                        gui.appendText(line);
                    }
                } catch (IOException ex) {
                    Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
                }

            } catch (IOException e) {
            }
        }
    }
}

客户端:

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

public class client {

    private Socket s;
    private String Name;
    private GUI gui;
    private Writer output;
    private BufferedReader input;

    public void start() {

        try {
            s = new Socket("127.0.0.1", 1234);
        } catch (IOException ex) {

        }
        try {
            input = new BufferedReader(new InputStreamReader(s.getInputStream()));
            output = new OutputStreamWriter(s.getOutputStream());
        } catch (IOException eIO) {

        }
        Name = gui.getName();
        new GUI(Name, output);
        new ListenFromServer().start();

    }

    public static void main(String[] args) {
        client cl = new client();
        GUI gui = new GUI();
        gui.creatServer();
    }

    class ListenFromServer extends Thread {

        public void run() {
            try {
                String line;
                while ((line = input.readLine()) != null) {
                    gui.appendText(line);
                }
            } catch (IOException ex) {
                Logger.getLogger(client.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

    }

}

我知道我的问题有点麻烦，但我真的很感激能帮助我解决这个问题!

Answer 1

我正在查看您的代码，很明显 output是 null当您尝试output.write(line + "\n");时因此我去寻找可能离开output的执行路径。未初始化。这就是调试非常方便的地方。

这是您的执行路径:

在 client 的主要方法中您创建一个新的 GUI然后调用gui.creatServer();

public static void main(String[] args) {
    client cl = new client();
    GUI gui = new GUI();
    gui.creatServer();
}

输出尚未分配且仍为空

在 creatServer();方法你有这一行:

    fldName.addMouseListener(new handler());

其中actionPerformed方法handler调用clients();具有以下行的方法:

fldText.addActionListener(new textSend(getName(), output));

注意output 仍然为空

(现在你的 textSend 类在构造函数中甚至没有做任何事情，但除此之外，即使它做了，你仍然使用 output 类中的 GUI 变量)

你有actionPerformed textSend中的方法具有以下行的类:

output.write(line + "\n");

无需初始化output它仍然为空，这给你 NullPointer

请参阅What is a NullPointerException, and how do I fix it?正如评论中链接的@markspace。此外，你应该真正学习如何调试小程序。

请参阅以下链接:

http://ericlippert.com/2014/03/05/how-to-debug-small-programs/ http://blogs.msdn.com/b/smallbasic/archive/2012/10/09/how-to-debug-small-basic-programs.aspx

此外，请考虑使用 Anonymous类来简化这些代码行，这也使代码更易于调试且更具可读性。

最后一个想法，记住使用标准 Naming Conventions对于您正在使用的语言。您的代码当前有很多不正确的小写类和一些大写方法/属性。