Java Swing GUI 客户端和服务器聊天应用程序 TextArea 未更新

Question

我正在为 GUI 使用 Java 和 Swing class 开发聊天应用程序。

ChatServer class 将是从客户端接收消息并回显给所有客户端的服务器，但我只打算为 2 个客户端进行聊天。

ChatClientclass都是客户端。它们在文本区域显示从服务器发送的内容。并将文本字段中的文本发送到服务器。

聊天客户端Class

package chatclient;

import java.net.Socket;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.InputStreamReader;

public class ChatClient extends javax.swing.JFrame {


public ChatClient() {
    initComponents();
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    scrollPane = new javax.swing.JScrollPane();
    textArea = new javax.swing.JTextArea();
    btnConnect = new javax.swing.JButton();
    btnDisconnect = new javax.swing.JButton();
    lblStatus = new javax.swing.JLabel();
    lblShowStatus = new javax.swing.JLabel();
    txtInput = new javax.swing.JTextField();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("Chat Client A");

    textArea.setEditable(false);
    textArea.setColumns(20);
    textArea.setRows(5);
    textArea.setText("Welcome to the Chat Server. Type '/close' or Click 'Disconnect' to close.");
    textArea.setWrapStyleWord(true);
    textArea.setCaretPosition(textArea.getDocument().getLength());
    scrollPane.setViewportView(textArea);

    btnConnect.setText("Connect");
    btnConnect.setActionCommand("btnConnect");
    btnConnect.addMouseListener(new java.awt.event.MouseAdapter() {
        public void mouseClicked(java.awt.event.MouseEvent evt) {
            btnConnectMouseClicked(evt);
        }
    });

    btnDisconnect.setText("Disconnect");
    btnDisconnect.setActionCommand("btnDisconnect");
    btnDisconnect.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            btnDisconnectActionPerformed(evt);
        }
    });

    lblStatus.setText("Status: ");

    lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
    lblShowStatus.setForeground(new java.awt.Color(255, 51, 51));
    lblShowStatus.setText("Disconnected");

    txtInput.setToolTipText("");
    txtInput.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            txtInputActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(scrollPane)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(btnConnect)
                    .addGap(18, 18, 18)
                    .addComponent(btnDisconnect)
                    .addGap(42, 42, 42)
                    .addComponent(lblStatus)
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                    .addComponent(lblShowStatus)
                    .addGap(0, 42, Short.MAX_VALUE))
                .addComponent(txtInput))
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(scrollPane, javax.swing.GroupLayout.PREFERRED_SIZE, 213, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 11, Short.MAX_VALUE)
            .addComponent(txtInput, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(btnConnect)
                .addComponent(btnDisconnect)
                .addComponent(lblStatus)
                .addComponent(lblShowStatus))
            .addContainerGap())
    );

    pack();
}// </editor-fold>                        

private void btnConnectMouseClicked(java.awt.event.MouseEvent evt) {                                        
    // TODO add your handling code here:
    lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
    lblShowStatus.setForeground(new java.awt.Color(0, 204, 51));
    lblShowStatus.setText("Connected");

    // ADD CODES FOR CONNECTING TO CHAT SERVER

}                                       

private void btnDisconnectActionPerformed(java.awt.event.ActionEvent evt) {                                              
    // TODO add your handling code here:
    lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
    lblShowStatus.setForeground(new java.awt.Color(255, 51, 51));
    lblShowStatus.setText("Disconnected");

    // ADD CODES FOR DISCONNECTING FROM CHAT SERVER

}                                             

private void txtInputActionPerformed(java.awt.event.ActionEvent evt) {                                         
    // TODO add your handling code here:
}                                        

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>      

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new ChatClient().setVisible(true);
        }
    });

    String input = "", serverInput = "";
    String host = "localhost";
    int port = 1337;
    Socket client;

    // updateTextArea("TEST UPDATE");

    try {
        client = new Socket(host, port);
        System.out.println("Connected to Server!");

        DataInputStream in = new DataInputStream(client.getInputStream());
        DataOutputStream out = new DataOutputStream(client.getOutputStream());

        System.out.println("Before setting text area");
        updateTextArea("trying to update");

        do {
            // HANDLE INPUT PART HERE
            serverInput = in.readUTF();


            if(serverInput != null) {
                System.out.println("Reached here");
                System.out.println(serverInput);
                updateTextArea(serverInput); 
            }

        } while(!input.equals("/close"));
        System.out.println("Program closed");
    }    

    catch(Exception exc) {
        System.err.println(exc.getMessage());
    }


}

private static void updateTextArea(String temp) {
    textArea.setText(textArea.getText() + "\n" + temp + "\n");
    textArea.setCaretPosition(textArea.getDocument().getLength());
}

// Variables declaration - do not modify                     
private javax.swing.JButton btnConnect;
private javax.swing.JButton btnDisconnect;
private javax.swing.JLabel lblShowStatus;
private javax.swing.JLabel lblStatus;
private javax.swing.JScrollPane scrollPane;
private static javax.swing.JTextArea textArea;
private javax.swing.JTextField txtInput;
// End of variables declaration                   
}

聊天服务器Class

package chatserver;

import java.io.BufferedReader;
import java.io.InputStreamReader;
// for testing
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

/**
 *
 * @author wacats
 */
public class ChatServer {
public static void main(String args[]) {
    int port = 1337;

    try {
        ServerSocket server = new ServerSocket(port);
        String inMessage = "";

        while(true) {
            Socket clientA = server.accept();
            DataInputStream inA = new DataInputStream(clientA.getInputStream());
            DataOutputStream outA = new DataOutputStream(clientA.getOutputStream());
            // outA.writeUTF("Welcome to the Chat Server. Type '/close' or Click 'Disconnect' to close.");

            // for testing
            // BufferedReader user = new BufferedReader(new InputStreamReader(System.in));

            do {
                inMessage = inA.readUTF();

                outA.writeUTF("testing");

                if(inMessage != null) {
                   outA.writeUTF(inMessage); 
                }

            } while(!inMessage.equals("/close"));
            clientA.close();
        }



    }

    catch(Exception ex) {
        ex.printStackTrace();
    }
}
}

我对这个程序的流程的看法是：

启动聊天服务器
启动聊天客户端
当两个客户端都连接到服务器后，他们就可以开始聊天了。
按"Enter" 会将文本字段中的文本发送到服务器。
服务器会将文本广播给两个客户端。
客户端将更新附加从服务器收到的文本的文本区域。

Answer 1

基本问题是，当您尝试调用 updateTextArea 时，textArea 是 null，这是因为 invokeLater 调用尚未执行并构建您的UI，你基本上有一个竞争条件。

在 Swing 中处理 Sockets 的正常方法是，使用 SwingWorker

查看 Concurrency in Swing and Worker Threads and SwingWorker 了解更多详情。

有多种方法可以解决您的问题。您可以使用 SwingWorker 从套接字读取文本并生成更新通知（通过 publish/process）方法，这通常称为 "observer pattern"。这很好，因为它可以解耦您的代码并生成更可重用的解决方案。

`SocketReader`

所有这些 class 所做的就是从 Socket 读取文本并从文本生成 ActionEvents，很简单。

public class SocketReader extends SwingWorker<Void, String> {

    private List<ActionListener> actionListeners;

    public SocketReader() {
        actionListeners = new ArrayList<>(25);
    }

    public void addActionListener(ActionListener listener) {
        actionListeners.add(listener);
    }

    public void removeActionListener(ActionListener listener) {
        actionListeners.remove(listener);
    }

    @Override
    protected Void doInBackground() throws Exception {
        System.out.println("Connected to Server!");

        try (DataInputStream in = new DataInputStream(SocketManager.INSTACNE.getInputStream())) {

            System.out.println("Before setting text area");

            String serverInput = null;
            do {
                // HANDLE INPUT PART HERE
                serverInput = in.readUTF();

                if (serverInput != null) {
                    System.out.println("Read " + serverInput);
                    publish(serverInput);
                }

            } while (!serverInput.equals("/close"));
            System.out.println("Program closed");
        }
        return null;
    }

    @Override
    protected void process(List<String> chunks) {
        for (String text : chunks) {
            ActionEvent evt = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, text);
            for (ActionListener listener : actionListeners) {
                listener.actionPerformed(evt);
            }
        }
    }

}

`SocketWriter`

这个简单的将文本写入Socket，简单。从技术上讲，您不需要为此使用 SwingWorker，但我喜欢这样一个事实，它相对容易取消

public class SocketWriter extends SwingWorker<Void, Void> {

    private List<String> messages;
    private ReentrantLock lock;
    private Condition waitCon;

    public SocketWriter() {
        messages = Collections.synchronizedList(new ArrayList<String>(25));
        lock = new ReentrantLock();
        waitCon = lock.newCondition();
    }

    public void write(String text) {
        System.out.println("Write " + text);
        messages.add(text);
        try {
            lock.lock();
            waitCon.signalAll();
        } finally {
            lock.unlock();
        }
    }

    @Override
    protected Void doInBackground() throws Exception {
        try (DataOutputStream out = new DataOutputStream(SocketManager.INSTACNE.getOutputStream())) {
            while (!isCancelled()) {
                while (messages.isEmpty() && !isCancelled()) {
                    try {
                        lock.lock();
                        waitCon.await();
                    } finally {
                        lock.unlock();
                    }
                }
                List<String> cache = new ArrayList<>(messages);
                messages.clear();
                for (String text : cache) {
                    System.out.println("Send " + text);
                    out.writeUTF(text);
                }
            }
        }
        return null;
    }

}

`SocketManager`

好吧，这对我来说有点矫枉过正，但我想要一个 Socket 的中央控制器，你不必使用单例，你可以简单地把它做成一个简单的 class 并将它的引用传递给你的 ChatClient 并向下传递给 SocketReader/Writer，但已经晚了，我很懒惰

public enum SocketManager {
    INSTACNE;

    private String host = "localhost";
    private int port = 1337;
    private Socket socket;

    public Socket open() throws IOException {
        if (socket != null) {
            close();
        }
        socket = new Socket(host, port);
        return socket;
    }

    public void close() throws IOException {
        if (socket == null) {
            return;
        }
        socket.close();
    }

    public boolean isOpen() {
        return socket != null
            && socket.isConnected()
            && !socket.isClosed()
            && !socket.isInputShutdown()
            && !socket.isOutputShutdown();
    }

    public InputStream getInputStream() throws IOException {
        Objects.requireNonNull(socket, "Socket is not open");
        return socket.getInputStream();
    }

    public OutputStream getOutputStream() throws IOException {
        Objects.requireNonNull(socket, "Socket is not open");
        return socket.getOutputStream();
    }
}

`ChatClient`

这一切都很棒，但你打算如何使用它？

基本上，您会在 ChatClient 中创建 SocketReader 和 SocketWriter 的实例，然后将 ActionListener 附加到 reader 并且触发时更新 JTextArea 并将您要发送的文本发送到 SocketWriter，例如...

public class ChatClient extends javax.swing.JFrame {

    public ChatClient() {
        initComponents();
        socketReader = new SocketReader();
        socketReader.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String text = e.getActionCommand();
                textArea.append(text);
                textArea.append("\n");
                textArea.setCaretPosition(textArea.getDocument().getLength());
            }
        });
        socketReader.execute();

        socketWriter = new SocketWriter();
        socketWriter.execute();
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        scrollPane = new javax.swing.JScrollPane();
        textArea = new javax.swing.JTextArea();
        btnConnect = new javax.swing.JButton();
        btnDisconnect = new javax.swing.JButton();
        lblStatus = new javax.swing.JLabel();
        lblShowStatus = new javax.swing.JLabel();
        txtInput = new javax.swing.JTextField();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setTitle("Chat Client A");

        textArea.setEditable(false);
        textArea.setColumns(20);
        textArea.setRows(5);
        textArea.setText("Welcome to the Chat Server. Type '/close' or Click 'Disconnect' to close.");
        textArea.setWrapStyleWord(true);
        textArea.setCaretPosition(textArea.getDocument().getLength());
        scrollPane.setViewportView(textArea);

        btnConnect.setText("Connect");
        btnConnect.setActionCommand("btnConnect");
        btnConnect.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                btnConnectMouseClicked(evt);
            }
        });

        btnDisconnect.setText("Disconnect");
        btnDisconnect.setActionCommand("btnDisconnect");
        btnDisconnect.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnDisconnectActionPerformed(evt);
            }
        });

        lblStatus.setText("Status: ");

        lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        lblShowStatus.setForeground(new java.awt.Color(255, 51, 51));
        lblShowStatus.setText("Disconnected");

        txtInput.setToolTipText("");
        txtInput.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                txtInputActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addComponent(scrollPane)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(btnConnect)
                        .addGap(18, 18, 18)
                        .addComponent(btnDisconnect)
                        .addGap(42, 42, 42)
                        .addComponent(lblStatus)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                        .addComponent(lblShowStatus)
                        .addGap(0, 42, Short.MAX_VALUE))
                    .addComponent(txtInput))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(scrollPane, javax.swing.GroupLayout.PREFERRED_SIZE, 213, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 11, Short.MAX_VALUE)
                .addComponent(txtInput, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(btnConnect)
                    .addComponent(btnDisconnect)
                    .addComponent(lblStatus)
                    .addComponent(lblShowStatus))
                .addContainerGap())
        );

        pack();
    }// </editor-fold>                        

    private void btnConnectMouseClicked(java.awt.event.MouseEvent evt) {
        // TODO add your handling code here:
        lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        lblShowStatus.setForeground(new java.awt.Color(0, 204, 51));
        lblShowStatus.setText("Connected");

        // ADD CODES FOR CONNECTING TO CHAT SERVER
    }

    private void btnDisconnectActionPerformed(java.awt.event.ActionEvent evt) {
        // TODO add your handling code here:
        lblShowStatus.setFont(new java.awt.Font("Tahoma", 1, 11)); // NOI18N
        lblShowStatus.setForeground(new java.awt.Color(255, 51, 51));
        lblShowStatus.setText("Disconnected");

        // ADD CODES FOR DISCONNECTING FROM CHAT SERVER
    }

    private void txtInputActionPerformed(java.awt.event.ActionEvent evt) {
        if (SocketManager.INSTACNE.isOpen()) {
            socketWriter.write(txtInput.getText());
        } else {
            System.out.println("!! Not open");
        }
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {

        try {
            /* Set the Nimbus look and feel */
            //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
            /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
            * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
             */
            try {
                for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                    if ("Nimbus".equals(info.getName())) {
                        javax.swing.UIManager.setLookAndFeel(info.getClassName());
                        break;
                    }
                }
            } catch (ClassNotFoundException ex) {
                java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (InstantiationException ex) {
                java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (IllegalAccessException ex) {
                java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            } catch (javax.swing.UnsupportedLookAndFeelException ex) {
                java.util.logging.Logger.getLogger(ChatClient.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
            }
            //</editor-fold>

            SocketManager.INSTACNE.open();

            /* Create and display the form */
            java.awt.EventQueue.invokeLater(new Runnable() {
                public void run() {
                    new ChatClient().setVisible(true);
                }
            });

        } catch (IOException ex) {
            ex.printStackTrace();
        }
        //</editor-fold>      

    }

    private SocketWriter socketWriter;
    private SocketReader socketReader;

    // Variables declaration - do not modify                     
    private javax.swing.JButton btnConnect;
    private javax.swing.JButton btnDisconnect;
    private javax.swing.JLabel lblShowStatus;
    private javax.swing.JLabel lblStatus;
    private javax.swing.JScrollPane scrollPane;
    private javax.swing.JTextArea textArea;
    private javax.swing.JTextField txtInput;
    // End of variables declaration                   
}

您会注意到，我在 main 中使用了 SocketManager#open，抱歉，错过了您的 "connect" 代码。我建议改为将其移至该方法 ;)

`ChatServer`

我没有对此做太多改动，但以防万一...

public class ChatServer {

    public static void main(String args[]) {
        int port = 1337;

        try {
            ServerSocket server = new ServerSocket(port);
            String inMessage = "";

            while (true) {
                System.out.println("Waiting");
                Socket clientA = server.accept();
                System.out.println("Connected");
                DataInputStream inA = new DataInputStream(clientA.getInputStream());
                DataOutputStream outA = new DataOutputStream(clientA.getOutputStream());
                // outA.writeUTF("Welcome to the Chat Server. Type '/close' or Click 'Disconnect' to close.");

                // for testing
                // BufferedReader user = new BufferedReader(new InputStreamReader(System.in));
                do {
                    inMessage = inA.readUTF();

                    if (inMessage != null) {
                        outA.writeUTF(inMessage);
                    }

                } while (!inMessage.equals("/close"));
                clientA.close();
            }

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

通常，当客户端连接时，您会启动一个新的 Thread 并让它处理客户端 Socket，但这不是我的重点。

因此，基于所有这些，您需要阅读大量书籍，包括 Concurrency in Java and All About Sockets

Java Swing GUI 客户端和服务器聊天应用程序 TextArea 未更新

Java Swing GUI Client and Server Chat App TextArea not updating

java

user-interface

swing

textarea

`SocketReader`

`SocketWriter`

`SocketManager`

`ChatClient`

`ChatServer`