客戶端 - 服務器應用程序空指針異常

我正在研究一個包含做客戶端 - 服務器聊天應用程序的迷你項目。該應用程序有一個GUI，我的問題是，我試圖從GUI獲取信息並連接到該服務器，但我收到一個空指針異常。到目前爲止，我有這個代碼的客戶端（服務器沒有GUI客戶端測試，並完美地工作）。客戶端 - 服務器應用程序空指針異常

的GUI類：

package tema09client; 
public class GUI extends javax.swing.JFrame { 
    Comunicare test; 
    String host, port, uname; 
    int init=0; 

    public GUI() { 
     initComponents(); 
    } 
    @SuppressWarnings("unchecked") 
    // <editor-fold defaultstate="collapsed" desc="Generated Code">       
    private void initComponents() { 

     jPanel1 = new javax.swing.JPanel(); 
     jLabel1 = new javax.swing.JLabel(); 
     jLabel2 = new javax.swing.JLabel(); 
     jTextField1 = new javax.swing.JTextField(); 
     jLabel3 = new javax.swing.JLabel(); 
     jTextField2 = new javax.swing.JTextField(); 
     jLabel4 = new javax.swing.JLabel(); 
     jTextField3 = new javax.swing.JTextField(); 
     jButton1 = new javax.swing.JButton(); 

     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
     setTitle("Network chat"); 
     setBackground(new java.awt.Color(255, 255, 255)); 
     setCursor(new java.awt.Cursor(java.awt.Cursor.DEFAULT_CURSOR)); 

     jPanel1.setBackground(new java.awt.Color(255, 255, 255)); 

     jLabel1.setText("Pentru a va loga selectati host-ul si portul, apoi scrieti-va username-ul in causta si apasati OK."); 

     jLabel2.setText("HOST"); 

     jTextField1.addActionListener(new java.awt.event.ActionListener() { 
      public void actionPerformed(java.awt.event.ActionEvent evt) { 
       jTextField1ActionPerformed(evt); 
      } 
     }); 

     jLabel3.setText("PORT"); 

     jLabel4.setText("USERNAME"); 

     jButton1.setText("Connect"); 
     jButton1.addActionListener(new java.awt.event.ActionListener() { 
      public void actionPerformed(java.awt.event.ActionEvent evt) { 
       jButton1ActionPerformed(evt); 
      } 
     }); 

     javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1); 
     jPanel1.setLayout(jPanel1Layout); 
     jPanel1Layout.setHorizontalGroup(
      jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(jPanel1Layout.createSequentialGroup() 
       .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
        .addGroup(jPanel1Layout.createSequentialGroup() 
         .addGap(79, 79, 79) 
         .addComponent(jLabel1)) 
        .addGroup(jPanel1Layout.createSequentialGroup() 
         .addGap(55, 55, 55) 
         .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
          .addGroup(jPanel1Layout.createSequentialGroup() 
           .addComponent(jLabel3) 
           .addGap(18, 18, 18) 
           .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, 57, javax.swing.GroupLayout.PREFERRED_SIZE) 
           .addGap(132, 132, 132) 
           .addComponent(jButton1)) 
          .addGroup(jPanel1Layout.createSequentialGroup() 
           .addComponent(jLabel2) 
           .addGap(18, 18, 18) 
           .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, 114, javax.swing.GroupLayout.PREFERRED_SIZE) 
           .addGap(84, 84, 84) 
           .addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 72, javax.swing.GroupLayout.PREFERRED_SIZE) 
           .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) 
           .addComponent(jTextField3, javax.swing.GroupLayout.DEFAULT_SIZE, 155, Short.MAX_VALUE))))) 
       .addGap(81, 81, 81)) 
     ); 
     jPanel1Layout.setVerticalGroup(
      jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addGroup(jPanel1Layout.createSequentialGroup() 
       .addContainerGap() 
       .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 23, javax.swing.GroupLayout.PREFERRED_SIZE) 
       .addGap(37, 37, 37) 
       .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
        .addComponent(jLabel2, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jTextField1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jLabel4, javax.swing.GroupLayout.PREFERRED_SIZE, 18, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jTextField3, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)) 
       .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED) 
       .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE) 
        .addComponent(jLabel3, javax.swing.GroupLayout.PREFERRED_SIZE, 22, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jTextField2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE) 
        .addComponent(jButton1)) 
       .addContainerGap(185, Short.MAX_VALUE)) 
     ); 

     javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane()); 
     getContentPane().setLayout(layout); 
     layout.setHorizontalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
     ); 
     layout.setVerticalGroup(
      layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING) 
      .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE) 
     ); 

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

    private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {            

    }           

    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {           
     try{ 
     if(init==0){ 
       host=jTextField1.getText(); 
       port=jTextField2.getText(); 
       System.out.println(host+" "+port); 
       if((host!=null) && (port!=null)){ 
        test=new Comunicare(host, Integer.getInteger(port)); 
        test.start(); 
        init=1; 
       } 
      } 

     test.setMesaj("cheieloginStep1"); 
     uname=jTextField3.getText(); 
     test.setUname(uname); 
     }catch (NullPointerException e) { 
       System.out.println(e); 
      } 
    }           


    // Variables declaration - do not modify      
    private javax.swing.JButton jButton1; 
    private javax.swing.JLabel jLabel1; 
    private javax.swing.JLabel jLabel2; 
    private javax.swing.JLabel jLabel3; 
    private javax.swing.JLabel jLabel4; 
    private javax.swing.JPanel jPanel1; 
    private javax.swing.JTextField jTextField1; 
    private javax.swing.JTextField jTextField2; 
    private javax.swing.JTextField jTextField3; 
    // End of variables declaration     

    public String getHost(){ 
     return jTextField1.getText(); 
    } 

    public String getPort(){ 
     return jTextField2.getText(); 
    } 

    public String getUsername(){ 
     return jTextField2.getText(); 
    } 
}

它連接到主機線程：

package tema09client; 

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

public class Comunicare extends Thread{ 
    Socket client=null; 
    PrintWriter out=null; 
    BufferedReader in=null; 
    boolean listen=true; 
    String username=null; 
    String mesaj=null; 

    public Comunicare(String host, int port){ 
     try { 
      client = new Socket(host, port); 
      out=new PrintWriter(client.getOutputStream()); 
      in=new BufferedReader(new InputStreamReader(client.getInputStream())); 
      //out.println("loginStep1"); 
     } catch (UnknownHostException ex) { 
      Logger.getLogger(Comunicare.class.getName()).log(Level.SEVERE, null, ex); 
     } catch (IOException ex) { 
      Logger.getLogger(Comunicare.class.getName()).log(Level.SEVERE, null, ex); 
     } 
    } 

    @Override 
    public void run(){ 
     String buffer; 
     String line; 
     while(listen){ 
      try { 
       out.flush(); 
       buffer = in.readLine(); 
       if(buffer.startsWith("cheie")){ 
        System.out.println("Serverul a trimis: "+buffer); 
        if(buffer.equals("cheieOKStep1")){ 
         out.println("cheieloginStep2"); 
         System.out.println("Am trimis: loginStep2"); 
         out.flush(); 
         logare(); 
        //out.flush(); 
        } 
        if(buffer.equals("cheieLoggedIn")){ 
        System.out.println("Conectat! ... se incarca lista de prieteni online."); 
        } 
        if(buffer.equals("cheieFail")) 
         System.out.println("Username-ul nu este in baza de date."); 
        if(buffer.equals("cheieActualizarePrieteni")) 
         System.out.println("Acum se adauga prietenii in lista"); 
       } 
       if(mesaj.startsWith("cheie")){ 
        if(mesaj.equals("cheieloginStep1")) 
         out.println(mesaj); 
       } 
      } catch (IOException ex) { 
       System.out.println(ex); 
      } 
     } 
    } 

    private void logare(){ 
     out.println(username); 
     System.out.println("Am trimis: "+username); 
    } 

    public void setUname(String user){ 
     username=user; 
    } 

    public void setMesaj(String mesaj){ 
     this.mesaj=mesaj; 
    } 
}

和主：

package tema09client; 
public class Main { 
    public static void main(String[] args) { 
     GUI fereastra=new GUI(); 
     fereastra.setVisible(true); 
    } 

}

我覺得這是堆棧跟蹤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException 
at tema09client.GUI.jButton1ActionPerformed(GUI.java:124) 
at tema09client.GUI.access$100(GUI.java:2) 
at tema09client.GUI$2.actionPerformed(GUI.java:48) 
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995) 
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)

等。這是來自GUI的第124行：test = new Comunicare（host，Integer.getInteger（port））;

任何人都可以幫助我嗎？ PS：當我按下「連接」按鈕時，空指針異常會觸發。

來源

2011-04-25 Ionut Ungureanu

我建議1）發佈堆棧跟蹤和2）只發布相關的代碼。 – 2011-04-25 23:32:17

發佈相關代碼是什麼意思？我如何獲得堆棧跟蹤？（我在NetBeans中工作） – 2011-04-25 23:36:54

堆棧跟蹤應該出現在控制檯或「輸出」中。 – 2011-04-25 23:38:44

使用Integer.parseInt(port)而不是Integer.getInteger(port)。 Integer.getInteger(port)用於從port指定的系統屬性中獲取整數，並且由於它返回null，並且您需要unboxInteger到int，您將獲得NPE。另外，你可能會在你的代碼的許多地方得到NPE，因爲你幾乎不檢查空值。您使用out,in,socket和buffer而不檢查是否爲空。

來源

2011-04-25 23:48:43 MByD

謝謝MByD！這是問題所在。現在它工作正常！ – 2011-04-25 23:52:43

@Ionut不要忘記接受每個問題的最佳答案。提出任何好的答案也是一個好主意。 – 2011-04-25 23:54:13

@lonut - 請閱讀已編輯的答案，因爲它很重要，而且'Integer.getInteger'返回'Integer'對象而不是'int'，它是原始的。 – MByD 2011-04-25 23:56:09

客戶端 - 服務器應用程序空指針異常

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