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我正在尝试学习网络编程。我的任务是使用 java swing 创建一个单线程客户端服务器聊天应用程序。我在更新 GUI 时遇到问题。我采用了一个 textarea 来显示消息和另一个 textarea 来发送消息。有一个按钮，您单击以发送消息。我正在使用计时器每 5 秒更新一次 GUI。应用程序运行。GUI 最初更新，然后屏幕冻结。谁能帮我？我想知道我哪里出错了。

package chattingapplication;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.Timer;

/**
 *
 * @author Qanita
 */
public class ServerMessenger extends javax.swing.JFrame {
    private int port;
    private ServerSocket server;
    private Socket client;
    private BufferedReader clientMessage;
    private PrintWriter serverMessage;
    private Timer timer;
    private ActionListener updateDisplay;
    private String receivingMessage;
    private String sendingMessage;

/**
 * Creates new form ServerMessenger
 */
public ServerMessenger() {
    initComponents();
    port = 13;
    try {
        server = new ServerSocket(port);
        client = null;
        client = server.accept();
        clientMessage = new BufferedReader(new InputStreamReader(client.getInputStream()));
        serverMessage = new PrintWriter(client.getOutputStream(), true);
        updateDisplay = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                receiveMessage();
                displayClientMessage();
                System.out.println("\nin timer");
            }
        };
        timer = new Timer(5000, updateDisplay);
        timer.setRepeats(true);
        timer.start();
    }
    catch (Exception e) {
        System.err.println(e);
    }
}

private void displayClientMessage()
{
    if ( receivingMessage != null )
    {
        receivingMessage = "\nClient : " + receivingMessage;
        displayArea.setText( displayArea.getText() + receivingMessage );
    }
}
private void displayServerMessage()
{
    sendingMessage = "\nServer : " + sendingMessage;
    displayArea.setText( displayArea.getText() + sendingMessage );
}
private void sendMessage()
{
    sendingMessage = writingArea.getText();
    serverMessage.println(sendingMessage);
}
private void receiveMessage()
{
    try {
        receivingMessage = clientMessage.readLine();
    } catch (IOException ex) {
        Logger.getLogger(ServerMessenger.class.getName()).log(Level.SEVERE, null, ex);
    }
}

/**
 * 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() {

    jScrollPane2 = new javax.swing.JScrollPane();
    displayArea = new javax.swing.JTextArea();
    jScrollPane1 = new javax.swing.JScrollPane();
    writingArea = new javax.swing.JTextArea();
    enter = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("Server");
    setResizable(false);

    displayArea.setEditable(false);
    displayArea.setColumns(20);
    displayArea.setLineWrap(true);
    displayArea.setRows(5);
    jScrollPane2.setViewportView(displayArea);

    writingArea.setColumns(20);
    writingArea.setRows(5);
    jScrollPane1.setViewportView(writingArea);

    enter.setText("Send");
    enter.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            enterActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jScrollPane2)
        .addGroup(layout.createSequentialGroup()
            .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 186, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(enter, javax.swing.GroupLayout.PREFERRED_SIZE, 61, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(0, 0, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addComponent(jScrollPane2, javax.swing.GroupLayout.DEFAULT_SIZE, 420, Short.MAX_VALUE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                .addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 0, Short.MAX_VALUE)
                .addComponent(enter, javax.swing.GroupLayout.PREFERRED_SIZE, 55, javax.swing.GroupLayout.PREFERRED_SIZE)))
    );

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

private void enterActionPerformed(java.awt.event.ActionEvent evt) {                                      
    sendMessage();
    writingArea.setText("");
    displayServerMessage();
}                                     

/**
 * @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(ServerMessenger.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(ServerMessenger.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(ServerMessenger.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(ServerMessenger.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            new ServerMessenger().setVisible(true);
        }
    });
}
// Variables declaration - do not modify                     
private javax.swing.JTextArea displayArea;
private javax.swing.JButton enter;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JScrollPane jScrollPane2;
private javax.swing.JTextArea writingArea;
// End of variables declaration

}

客户端类在逻辑上几乎相同，但有细微差别。但逻辑几乎相同。我想问题出在计时器上，但我无法弄清楚到底是什么问题。在这方面的任何帮助将不胜感激。

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1 回答 1

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BufferedReader.readLine() 在内部调用 java.io.Reader.read(char[], int, int)。因此，使用 Reader.read javadoc：“此方法将阻塞，直到某些输入可用”。

您应该冻结，因为 updateDisplay() 调用了调用 readLine() 的 receiveMessage() 并且没有数据可用。

于 2013-03-23T17:28:34.843 回答