Java、聊天、服务器发送、客户端接收都可以，但不能反过来.视频在youtube上观看问题

Question

如youtube上的视频所示，场景是

 http://youtu.be/5OwXqnZ64rE

是的，虽然服务器聊天窗口确实发送了消息，客户端收到并显示了这些消息，但它不能以相反的方式工作。

以下是三个类别：

Server:
package backend;
import frontend.Gui;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
 *
 * @author Natalochka
 */
public class Server implements ActionListener, Runnable {
    private ServerSocket ss;
    private Socket s;
    private ObjectOutputStream oos;
    private ObjectInputStream ois;    
    private Gui servertalkstogui;    
    public Server(Gui in ) {
        servertalkstogui = in;
    }    
    @Override
    public void actionPerformed(ActionEvent ae) {       
        if(ae.getSource() == servertalkstogui.getCreate()){
            servertalkstogui.getAreachat().append("This is the server: " + "n");
            Thread t = new Thread(this);
            t.start();          
        }
        if(ae.getSource() == servertalkstogui.getButton()){            
            String linea = servertalkstogui.getTextField().getText();
            servertalkstogui.getTextField().setText("");
            this.writeLine(linea);
        }
    }

    @Override
    public void run() {        
        try {
            ss = new ServerSocket(9999);
            s = ss.accept();
            oos = new ObjectOutputStream(s.getOutputStream());
            ois = new ObjectInputStream(s.getInputStream());  
            this.readLine();         
        } catch (IOException e) {           
            try { 
                this.closeServer();
            } catch (IOException ex) {
                System.out.println("se jodio");
                Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
            }
            e.getLocalizedMessage();        
        } catch (InterruptedException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }        
    }
    public void writeLine(String linea){        
        try {            
            oos.writeObject(linea);
            servertalkstogui.getAreachat().append("n I say: " + linea);            
        } catch (IOException e) {            
            e.getLocalizedMessage();
        }        
    }
    public void readLine() throws InterruptedException{        
        try {
            while(true){                
             Object aux = ois.readObject();
             if(aux != null && aux instanceof String){                 
              servertalkstogui.getAreachat().append("Client says: " + (String)aux + "n");
             }
         }
      } catch (IOException | ClassNotFoundException e) {
   }
}

    public void closeServer() throws IOException{
        try {
             oos.close();
             s.close();
             ss.close();
        } catch (Exception e) {
            e.addSuppressed(e);
        }
    }
}
CLIENT
package backend;
import frontend.Gui;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.Socket;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author Natalochka
 */
public class Client implements ActionListener, Runnable {
    private Socket s;
    private ObjectOutputStream oos;
    private ObjectInputStream ois;
    private Gui clienttalkstogui;

    public Client(Gui in){    
    clienttalkstogui = in;
}
    @Override
    public void actionPerformed(ActionEvent ae) {      
        // to connect to the socket that the Server opened
        if(ae.getSource() == clienttalkstogui.getConnect()){            
            Thread t = new Thread(this);
            t.start();         
        }
       // to obtain and send whatever was typed in the text field   
        if(ae.getSource() == clienttalkstogui.getButton()){            
            String linea = clienttalkstogui.getTextField().getText();
            this.writeLine(linea);            
        }
     }    
    @Override
     public void run() {
        try {
            s = new Socket("localhost", 9999);            
            oos = new ObjectOutputStream(s.getOutputStream());
            ois = new ObjectInputStream(s.getInputStream());  
            clienttalkstogui.getAreachat().append("Conected to port" + "n");
            this.readLine();
        } catch (IOException | InterruptedException ex) {
            Logger.getLogger(Client.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
      public void writeLine(String linea){        
        try { 
            // to send it to the server
            oos.writeObject(linea);
            // to have it displayed on the client window too
            clienttalkstogui.getAreachat().append(linea);
        } catch (IOException e) { 
            //this.closeClient();
            e.getLocalizedMessage();
        }
    }

    public void readLine() throws InterruptedException{        
        try {
            while(true){                
             Object aux = ois.readObject();
             if(aux != null && aux instanceof String){                 
              clienttalkstogui.getAreachat().append("Server says: " + (String)aux + "n");
             }
         }
      } catch (IOException | ClassNotFoundException e) {
   }
}  
   /*
    public void closeClient()
    {
        try {
            ois.close();
            oos.close();
            s.close();
        } catch (Exception e) {
            e.getLocalizedMessage();
        }

    }    
*/    

}

GUI

package frontend;
import backend.Client;
import backend.Server;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
/**
 *
 * @author Natalochka
 */
public class Gui extends JFrame{    
    private JMenuBar bar;
    private JMenu menu;
    private JMenuItem connect, create, exit;
    private JTextArea areachat;
    private JTextField campochat;
    private JButton botonchat;
    private JScrollPane scroll;
    /*WE CREATE INSTANTIATED OBJECTS OF CLASSES INTERACTING WITH THE GUI*/
    Server servidor = new Server(this);
    Client cliente = new Client(this);

    /*CREATING THE CONSTRUCTOR*/
    public Gui(){
        super("CHAT WINDOW");
        this.setSize(400, 500);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        /*INSTANTIATE THE OBJECTS*/
        bar = new JMenuBar();
        menu = new JMenu("Menu");
        connect = new JMenuItem("Conectar");
        create  = new JMenuItem("Crear");
        exit    = new JMenuItem("Salir");
        areachat  = new JTextArea();
        campochat = new JTextField(20);
        botonchat = new JButton("Send");
        scroll = new JScrollPane(areachat);
        /*THE BAR IS PLACED IN THE JFRAME WINDOW*/
        this.setJMenuBar(bar);
        /*THE MENU IS ADDED TO THE BAR*/
        bar.add(menu);
        /*THE ITEMS ARE ADDED TO THE MENU*/        
        menu.add(connect);
        menu.add(create);
        menu.add(exit);
        /*MAKE ITEMS LISTEN TO THE EVENT FROM THE CODE CLASSES*/
        create.addActionListener(servidor);
        connect.addActionListener(cliente);        
        exit.addActionListener(servidor);
        exit.addActionListener(cliente);
        botonchat.addActionListener(cliente);
        botonchat.addActionListener(servidor);

        /*CREATING THE LAYOUTS*/
        /*AREACHAT*/
        this.setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        gbc.gridx = 0;
        gbc.gridy = 0;
        gbc.gridwidth = 2;
        gbc.gridheight = 1;
        gbc.fill = GridBagConstraints.BOTH;
        gbc.weightx = 1;
        gbc.weighty = 1;
        this.add(scroll, gbc);
        /*TEXTFIELD*/
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        gbc.gridheight = 1;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.weightx = 1;
        gbc.weighty = 0;
        this.add(campochat,gbc);

       /*BOTON*/ 
        gbc.gridx = 1;
        gbc.gridy = 1;
        gbc.gridwidth = 1;
        gbc.gridheight = 1;
        gbc.weightx = 0;
        gbc.weighty = 0;
        this.add(botonchat, gbc);
        this.setVisible(true);

    }

       /*CREATING THE GETTERS AND SETTERS*/
    /*GETTERS*/
       public JTextArea  getAreachat(){        
           return areachat;         
    }
       public JMenuItem getCreate(){

           return create;
       }

       public JMenuItem getConnect(){
           return connect;
       }
      public JTextField getTextField(){
          return campochat;
      }
      public JButton getButton(){
          return botonchat;
      }
      /*SETTERS*/
 public static void main(String[] args) throws InterruptedException {

        Gui objeto = new Gui();
    }     
}

这是的错误日志

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at backend.Server.writeLine(Server.java:80)
    at backend.Server.actionPerformed(Server.java:48)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
    at java.awt.Component.processMouseEvent(Component.java:6525)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
    at java.awt.Component.processEvent(Component.java:6290)
    at java.awt.Container.processEvent(Container.java:2234)
    at java.awt.Component.dispatchEventImpl(Component.java:4881)
    at java.awt.Container.dispatchEventImpl(Container.java:2292)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
    at java.awt.Container.dispatchEventImpl(Container.java:2278)
    at java.awt.Window.dispatchEventImpl(Window.java:2739)
    at java.awt.Component.dispatchEvent(Component.java:4703)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
    at java.awt.EventQueue.access$400(EventQueue.java:97)
    at java.awt.EventQueue$3.run(EventQueue.java:697)
    at java.awt.EventQueue$3.run(EventQueue.java:691)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.awt.EventQueue$4.run(EventQueue.java:719)
    at java.awt.EventQueue$4.run(EventQueue.java:717)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
BUILD STOPPED (total time: 58 seconds)

Answer 1

我重写了我的全部答案：

您的代码有几个实现缺陷，这些缺陷使得读取、调试和生成错误变得困难。

您得到的NullPointerException是因为您在send按钮上设置了两个ActionListener（Client的侦听器和Server的侦听器）：

botonchat.addActionListener(cliente);
botonchat.addActionListener(servidor);

因此，无论您只为Server或Client设置变量，两者都会被调用，其中一个会有一些null变量->NullPointerException。

一个快速（肮脏）的修复方法是在使用变量oos之前检查是否已设置，并仅在读取数据时清除JTextField：

//Server
public void writeLine(String linea)
{
    try
    {
        if (this.oos != null)
        {
            oos.writeObject(linea);
            servertalkstogui.getTextField().setText("");//clearing JTextField
            servertalkstogui.getAreachat().append("n I say: " + linea);
        }
    }
    catch (IOException e)
    {
        e.getLocalizedMessage();
    }
}

//Client
public void writeLine(String linea)
{
    try
    {
        if (this.oos != null)
        {
            // to send it to the server
            oos.writeObject(linea);
            clienttalkstogui.getTextField().setText("");//clear the text when it have been read
            // to have it displayed on the client window too
            clienttalkstogui.getAreachat().append(linea);
        }
    }
    catch (IOException e)
    {
        // this.closeClient();
        e.getLocalizedMessage();
    }
}

删除actionPerformed:中JTextField的清除

//Server
@Override
public void actionPerformed(ActionEvent ae)
{
    if (ae.getSource() == servertalkstogui.getCreate()/* .getButton() */)
    {
        servertalkstogui.getAreachat().append("This is the server: " + "n");
        Thread t = new Thread(this);
        t.start();
    }
    if (ae.getSource() == servertalkstogui.getButton())
    {
        String linea = servertalkstogui.getTextField().getText();
        //servertalkstogui.getTextField().setText("");// do not clear the text here ! You don't know if it will be read yet. 
        this.writeLine(linea);
    }
}

这项工作没有任何Exception。

一个好的做法是将Client和Server的代码分开：没有理由在Gui中实例化这两个代码。