java - 客户端-服务器应用程序空指针异常

Question

我正在开发一个小型项目，其中包括制作客户端-服务器聊天应用程序。该应用程序有一个 GUI，我的问题是我试图从 GUI 获取信息并连接到该服务器，但我收到一个空指针异常。到目前为止，我已经有了客户端的代码(服务器在没有 GUI 客户端的情况下进行了测试，并且工作完美)。

GUI 类:

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();
    }
}

连接主机的线程:

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;
    }
}

主要内容:

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

}

我认为这是堆栈跟踪:

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。这是 GUI 中的第 124 行:test=new Comunicare(host, Integer.getInteger(port));

有人可以帮我吗？ PS:当我按下“连接”按钮时，会引发空指针异常。

Answer 1

使用Integer.parseInt(port)而不是Integer.getInteger(port)。 Integer.getInteger(port)用于从 port 指定的系统属性中获取整数，由于它返回 null，因此您需要 unbox将 Integer 转换为 int，您将得到 NPE。

此外，您可能会在代码中的许多地方得到 NPE，因为您几乎没有检查空值。您使用 out、in、socket 和 buffer 而不检查是否为 null。