我遇到了一个嵌入式applet的问题，我已经有一段时间了。 applet的jar被签名并授予所有权限，并且它在applet查看器中运行得非常好。在浏览器中加载时，只有一个空白框，其中包含我的applet的错误徽标。单击时返回“java.lang.invocationtargetexception”。我使用基本的HTML格式来嵌入applet。 这是我用来显示它的HTML代码：
<html>
<body background="BG.png">
<a href="index.html">Back to the index</a>
<center><h1>Web Forum</h1></center>
<center><table border = "0">
<tr>
<td><center><h3>Forums</h3></center></td>
<td width = 25></td>
<td width = 225><center><h3>Chatbox</h3></center></td>
</tr>
<tr>
<td><center><applet
code=Topics.class
archive=Topics.jar
width=750
height=1000 ><PARAM name="permissions" value="sandbox"></PARAM>
</applet></center></td>
<td width = 25></td>
<td width = 225 bgcolor = #00FF00><center><h3>Coming Soon</h3></center></td>
</tr>
</table></center>
</Body>
</Html>
这是Java控制台转储线程列表：
Dump thread list ...
Group main,ac=19,agc=2,pri=10
main,5,alive
traceMsgQueueThread,5,alive,daemon
Timer-0,5,alive
AWT-Shutdown,5,alive
AWT-Windows,6,alive,daemon
Java Plug-In Pipe Worker Thread (Client-Side),5,alive,daemon
AWT-EventQueue-0,6,alive
SysExecutionTheadCreator,5,alive,daemon
MemoryCache-DelayedCleanup,5,alive,daemon
CacheMemoryCleanUpThread,5,alive,daemon
Browser Side Object Cleanup Thread,5,alive
JVM[id=1]-Heartbeat,5,alive,daemon
Group Plugin Thread Group,ac=4,agc=0,pri=10
AWT-EventQueue-1,6,alive
Image Fetcher 0,8,alive,daemon
TimerQueue,5,alive,daemon
SysExecutionThead,5,alive,daemon
Group http://25.2.202.42/-threadGroup,ac=4,agc=0,pri=4
Applet 1 LiveConnect Worker Thread,4,alive
AWT-EventQueue-2,4,alive
TimerQueue,4,alive,daemon
ConsoleTraceListener,4,alive,daemon
Done.
这是签名jar的清单：
Manifest-Version: 1.0
Name: .classpath
SHA-256-Digest: IhqMeyTH+t/Wtxr+NP6B1f5GapLwQ67HJhYQ7UM+kA0=
Name: .project
SHA-256-Digest: Lw9C+yAb3p1vC6m2pwcjhv8TB1ET8xOYjM2sFlgIjIw=
Permissions: all-permissions
Codebase: http://25.2.202.42/
我认为没有理由从我的代码本身产生错误，但这里只是因为：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.applet.*;
import java.io.*;
@SuppressWarnings("serial")
public class Topics extends Applet {
String name;
String topics;
String paragraphs;
//reading file for existing posts
String fileread = "Topics.txt";
static String line = null;
{
try {
FileReader fileReader =
new FileReader(fileread);
BufferedReader bufferedReader =
new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
bufferedReader.close();
}
catch(FileNotFoundException ex) {
System.out.println(
"Unable to open file '" +
fileread + "'");
}
catch(IOException ex1) {
System.out.println(
"Error reading file '"
+ fileread + "'");
}
}
static String display = line;
JPanel topicPanel;
JLabel title, username, topic, paragraph, topicsTitle, dtopicsTitle;
JTextField nameField, topicField;
JButton submitButton, topicrefreshButton;
JTextArea paragraphArea, topicArea;
public void init() {
final JPanel topicGUI = new JPanel();
topicGUI.setLayout(null);
setBackground(Color.GREEN);
setVisible(true);
// JLabels
JLabel title = new JLabel(" Make A Post ");
title.setSize(150, 25);
title.setFont(new Font("Serif", Font.PLAIN, 25));
title.setHorizontalAlignment(0);
add(title);
JLabel username = new JLabel("Username: ");
username.setSize(70, 15);
username.setHorizontalAlignment(0);
add(username);
// JTextField
nameField = new JTextField(8);
nameField.setSize(150, 18);
add(nameField);
// JLabel
JLabel topic = new JLabel("Topic: ");
topic.setSize(40, 15);
topic.setHorizontalAlignment(0);
add(topic);
// JTextField
topicField = new JTextField(8);
topicField.setSize(180, 18);
add(topicField);
//JLabel
JLabel paragraph = new JLabel(" Paragraph: ");
paragraph.setSize(70, 15);
paragraph.setHorizontalAlignment(0);
add(paragraph);
// JTextAreas
paragraphArea = new JTextArea(8, 5);
paragraphArea.setSize(700, 100);
paragraphArea.setLineWrap(true);
paragraphArea.setEditable(true);
add(paragraphArea);
// JButton
JButton submitButton = new JButton("SUBMIT");
submitButton.setSize(100, 30);
submitButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
name = nameField.getText();
topics = topicField.getText();
paragraphs = paragraphArea.getText();
display ="\n" + "\t" + name + " - " + "\n" + "\t" + topics + " : " + "\n" + paragraphs + display + "\n";
topicField.setText("");
paragraphArea.setText("");
//writing new info to file
String fileName = "Topics.txt";
try {
FileWriter fileWriter =
new FileWriter(fileName);
BufferedWriter bufferedWriter =
new BufferedWriter(fileWriter);
bufferedWriter.write(display);
bufferedWriter.close();
}
catch(IOException ex) {
System.out.println(
"Error writing to file '"
+ fileName + "'");
}
topicArea.setText(display);
}
});
add(submitButton);
JLabel dtopicsTitle = new JLabel(" Topics: ");
dtopicsTitle.setLocation(170, 3);
dtopicsTitle.setSize(150,30);
dtopicsTitle.setFont(new Font("Serif", Font.PLAIN, 25));
dtopicsTitle.setHorizontalAlignment(0);
add(dtopicsTitle);
topicrefreshButton = new JButton("Refresh Topics");
topicrefreshButton.setLocation(250, 30);
topicrefreshButton.setSize(100, 30);
topicrefreshButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
topicArea.setText(display);
}
});
add(topicrefreshButton);
topicArea = new JTextArea(40, 64);
topicArea.setSize(650, 430);
topicArea.setLineWrap(true);
topicArea.setEditable(false);
topicArea.setText(display);
add(topicArea);
JScrollPane topicScroll = new JScrollPane(topicArea);
topicScroll.setSize(650,430);
add(topicScroll);
}
}
感谢您提供的任何支持。
答案 0 :(得分：1)
Applet和File混合如油和水（即'不'）。
任何File对象不仅不会指向您所期望的位置（它们指向用户的本地文件系统，而不是服务器），但是在它之前需要对applet进行数字签名和信任。可以使用文件。
Applet通常会通过URL访问资源。如果URL可以相对于applet的代码库，文档库或类路径形成，它可以保持沙盒并仍然有效。否则就需要信任它。
catch (Exception e) { ..的代码更改为catch (Exception e) { e.printStackTrace(); // very informative! .. JApplet代替Applet。）