我制作了一个小程序，它在 tcp 套接字上监听和发送线路，并将接收到的信息附加到 JTextArea。我用它在 Minecraft 服务器上聊天，而无需打开游戏。
我昨晚工作得很好，但当我起床时却不工作了。当我打开 netbeans 并运行它时，它给出了这个错误:
Exception in thread "main" java.lang.NullPointerException
at com.xxx.mcchat.chat.main(chat.java:333)
谁能解释一下哪里出了问题？
这是代码(http://pastebin.com/FPNty0qf):
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package com.xxx.mcchat;
import java.io.*;
import java.net.*;
import net.sf.json.*;
import org.apache.commons.beanutils.*;
import org.apache.commons.collections.*;
import org.apache.commons.lang.*;
import net.sf.ezmorph.*;
import org.apache.commons.logging.*;
import java.awt.event.*;
import javax.swing.UIManager;
/**
*
* @author xxx
*/
public class chat extends javax.swing.JFrame {
/**
* Creates new form chat
*/
public chat() {
initComponents();
}
public void send(String user, String message){
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
socket = new Socket("mc.xxx.net", 20060);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection");
System.exit(1);
}
BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
//System.out.println(in.readLine()); //Uncomment to debug
if(username != null){
out.println("/api/call?method=broadcast&args="+"[\"§7[Web] §b"+username+"§7:§f "+message+"\"]"+"&key=f0e2ad47a9a43c783d2c54f396f655c9279829c8c69ae9f52934648098dec993");
chatArea.append(username + ": " + message + "\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}else{
chatArea.append("You must set your username!!" + "\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}
}
/**
* 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() {
jCheckBoxMenuItem1 = new javax.swing.JCheckBoxMenuItem();
jToggleButton1 = new javax.swing.JToggleButton();
jScrollPane1 = new javax.swing.JScrollPane();
chatArea = new javax.swing.JTextArea();
input = new javax.swing.JTextField();
send = new javax.swing.JButton();
user = new javax.swing.JTextField();
userset = new javax.swing.JButton();
autoscrollCheck = new javax.swing.JCheckBox();
jLabel1 = new javax.swing.JLabel();
jCheckBoxMenuItem1.setSelected(true);
jCheckBoxMenuItem1.setText("jCheckBoxMenuItem1");
jToggleButton1.setText("jToggleButton1");
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
setTitle("Minecraft Chat");
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowOpened(java.awt.event.WindowEvent evt) {
formWindowOpened(evt);
}
public void windowClosing(java.awt.event.WindowEvent evt) {
formWindowClosing(evt);
}
});
chatArea.setEditable(false);
chatArea.setBackground(new java.awt.Color(0, 0, 0));
chatArea.setColumns(20);
chatArea.setFont(new java.awt.Font("Consolas", 0, 14)); // NOI18N
chatArea.setForeground(new java.awt.Color(255, 255, 255));
chatArea.setLineWrap(true);
chatArea.setRows(5);
jScrollPane1.setViewportView(chatArea);
input.setToolTipText("Enter message here");
input.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyPressed(java.awt.event.KeyEvent evt) {
inputKeyPressed(evt);
}
});
send.setText("Send");
send.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
sendActionPerformed(evt);
}
});
user.setToolTipText("");
user.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
userActionPerformed(evt);
}
});
user.addKeyListener(new java.awt.event.KeyAdapter() {
public void keyPressed(java.awt.event.KeyEvent evt) {
userKeyPressed(evt);
}
});
userset.setText("Set");
userset.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
usersetActionPerformed(evt);
}
});
autoscrollCheck.setSelected(true);
autoscrollCheck.setText("Auto Scroll");
autoscrollCheck.addActionListener(new java.awt.event.ActionListener() {
public void actionPerformed(java.awt.event.ActionEvent evt) {
autoscrollCheckActionPerformed(evt);
}
});
jLabel1.setText("Enter Username:");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(10, 10, 10)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(jLabel1)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(user, javax.swing.GroupLayout.PREFERRED_SIZE, 218, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
.addComponent(userset)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(autoscrollCheck))
.addComponent(jScrollPane1)
.addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
.addComponent(input, javax.swing.GroupLayout.PREFERRED_SIZE, 649, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
.addComponent(send)))
.addGap(10, 10, 10))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(11, 11, 11)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(1, 1, 1)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
.addComponent(user, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(jLabel1)))
.addComponent(userset)
.addComponent(autoscrollCheck))
.addGap(6, 6, 6)
.addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 316, Short.MAX_VALUE)
.addGap(6, 6, 6)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGap(1, 1, 1)
.addComponent(input, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
.addComponent(send))
.addGap(11, 11, 11))
);
pack();
}// </editor-fold>
String username = null;
private void inputKeyPressed(java.awt.event.KeyEvent evt) {
int key = evt.getKeyCode();
if (key == KeyEvent.VK_ENTER) {
send(username, input.getText());
input.setText("");
}
}
private void sendActionPerformed(java.awt.event.ActionEvent evt) {
send(username, input.getText());
input.setText("");
}
private void usersetActionPerformed(java.awt.event.ActionEvent evt) {
if(username == null){
if(!"".equals(user.getText())){
username = user.getText();
chatArea.append("Username set!"+"\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}else{
chatArea.append("Username can not be blank."+"\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}
}else{
send(username, "§7changed name to " + user.getText());
username = user.getText();
}
}
private void userActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
private void userKeyPressed(java.awt.event.KeyEvent evt) {
int key = evt.getKeyCode();
if (key == KeyEvent.VK_ENTER) {
if(username == null){
if(!"".equals(user.getText())){
username = user.getText();
chatArea.append("Username set!"+"\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}else{
chatArea.append("Username can not be blank."+"\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}
}else{
send(username, "§7changed name to " + user.getText());
username = user.getText();
}
}
}
private void formWindowClosing(java.awt.event.WindowEvent evt) {
}
private void formWindowOpened(java.awt.event.WindowEvent evt) {
// TODO add your handling code here:
}
private void autoscrollCheckActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) throws IOException {
/* Set the system look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code ">
/* 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 {
javax.swing.UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(chat.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(chat.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(chat.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(chat.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 chat().setVisible(true);
}
});
Socket socket = null;
PrintWriter out = null;
BufferedReader in = null;
try {
socket = new Socket("mc.xxx.net", 20060);
out = new PrintWriter(socket.getOutputStream(), true);
in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
} catch (UnknownHostException e) {
System.err.println("Don't know about host");
System.exit(1);
} catch (IOException e) {
System.err.println("Couldn't get I/O for the connection");
System.exit(1);
}
BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
//System.out.println(in.readLine()); //Uncomment to debug
out.println("/api/subscribe?source=chat&key=1e287587f5d1d45255f4708467eeaf8a71085f9ccfd8a354523d233cf5a77be4&show_previous=true");
out.println("/api/subscribe?source=connections&key=e410592b70c0288654e6c1040edb0f21811dcb3f2ee11051163f36be9be00788&show_previous=false");
while(true){
String jsonString = in.readLine();
JSONObject obj = JSONObject.fromObject(jsonString);
JSONObject success = obj.getJSONObject("success");
if(success.get("message") != null){
chatArea.append("<" + success.get("player") + "> " + success.get("message") + "\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}else if (success.get("action") != null){
chatArea.append(success.get("player") + " " + success.get("action") + "\n\r");
if(autoscrollCheck.isSelected()){
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}
}
}
// Variables declaration - do not modify
public static javax.swing.JCheckBox autoscrollCheck;
public static javax.swing.JTextArea chatArea;
private javax.swing.JTextField input;
private javax.swing.JCheckBoxMenuItem jCheckBoxMenuItem1;
private javax.swing.JLabel jLabel1;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JToggleButton jToggleButton1;
private javax.swing.JButton send;
private javax.swing.JTextField user;
private javax.swing.JButton userset;
// End of variables declaration
}
(P.S 请不要生气，因为我使用的是 GUI 生成器，这是我的第一个程序，我保证我会学会手工制作)
最佳答案
在第 333 行，唯一可以为 null 的是 chatArea。 (如果 success 为 null，它会在第 332 行的 if 语句中抛出异常。)正如其他人所建议的那样，您可能有一个不存在的竞争条件在到达第 333 行之前被初始化。
修复它的正确方法是将 chatArea 调用包含在对 SwingUtilities.invokeLater 的调用中:
final JSONObject success = obj.getJSONObject("success");
SwingUtilities.invokeLater(new Runnable() {
public void run() {
if (success.get("message") != null) {
chatArea.append("<" + success.get("player") + "> " + success.get("message") + "\n\r");
if (autoscrollCheck.isSelected()) {
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
} else if (success.get("action") != null) {
chatArea.append(success.get("player") + " " + success.get("action") + "\n\r");
if (autoscrollCheck.isSelected()) {
chatArea.setCaretPosition(chatArea.getText().length() - 1);
}
}
}
});
任何时候对 Swing 组件进行更改，都应该在事件分派(dispatch)线程中调用它。更重要的是，由于 EDT 是单线程的、基于队列的执行器，这保证会等到您之前提交的可运行对象完成，所以 chatArea 肯定会被设置。
另一个注意事项:将 UIManager 调用也包装在 invokeLater 调用中通常是一种很好的做法。
编辑:我只是想更清楚地说明您应该始终在 invokeLater 调用中包装什么:
- 构建 Swing 组件
- 更改 Swing 组件的属性
- 修改 Swing 组件的数据模型(不一定获取数据，只是告诉关心它的组件发生了变化，例如触发事件，需要在 EDT 上发生)<
- 修改
UIManager属性，包括设置外观或修改其键值 - 实例化外观
- 实例化
ComponentUI的子类 - 在容器中添加和删除组件
不需要包装的东西:
更改尚未显示的组件的属性根据 Robin 在评论中的说法，这仍然需要在 EDT 上发生。- 调用
重绘 - 调用
validate或invalidate(我想，我需要对此进行确认)
执行所有这些操作，任何时候切换到新的外观和感觉时，您都不会遇到在 EDT 上未调用的事情的任何问题。
长话短说，Swing 不是线程安全的，因此您应该始终从事件分派(dispatch)线程调用 Swing 组件方法。
此外，我欢迎就我可能忘记的事情向我的列表提出任何建议。
下面是一些描述 Swing 中线程的资源:
关于java - 突然: java. lang.NullPointerException，昨晚还好好的，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13317806/