我正试图根据JFileChooser返回给我的文件实例化一个类。因此，到目前为止，我已经使JFileChooser工作，并且我可以成功地获取我正在查找的.class文件。然而，我在实际使用.class文件并用它创建对象时遇到了问题
这是我正在写的方法。。。
public static Agent loadAgentFromFile(File file){
Agent agent = null;
String fileName = file.getName();
String filePath = file.getAbsolutePath();
String parentDirectory = file.getParentFile().getName();
String agentClassName = fileName.substring(0, fileName.lastIndexOf('.'));
Object object = null;
//System.out.println(filePath.contains(parentDirectory));
//System.out.println(filePath.substring(0, filePath.indexOf(parentDirectory)));
try {
File f = new File(filePath.substring(0, filePath.indexOf(parentDirectory)));
URL[] cp = {f.toURI().toURL()};
URLClassLoader urlcl = new URLClassLoader(cp);
Class agentDefinition = null;
if (parentDirectory.equals("Agents"))
{
System.out.println(PACKAGE + agentClassName);
agentDefinition = urlcl.loadClass(PACKAGE + agentClassName);
//agentDefinition = Class.forName(PACKAGE + agentClassName);
}
else
{
System.out.println(PACKAGE + parentDirectory + "." + agentClassName);
agentDefinition = urlcl.loadClass(parentDirectory + "." + agentClassName);
}
object = agentDefinition.newInstance();
agent = (Agent)object;
}
catch (InstantiationException e) {
JOptionPane.showMessageDialog(THIS,
"The chosen class must not be an interface or be abstract, " +
"and it must not have any arguments in its constructor.");
}
catch (IllegalAccessException e) {
JOptionPane.showMessageDialog(THIS,
"The chosen class's constructor must be public.");
}
catch (ClassNotFoundException e) {
JOptionPane.showMessageDialog(THIS,
"The chosen class cannot be found. Make sure the .java file is compiled.");
}
catch (ClassCastException e) {
JOptionPane.showMessageDialog(THIS,
"The chosen class does not extend from the Agent class.");
}
catch (Exception e) {
e.printStackTrace(); //prints the stack to see what exception occurred that we didn't catch
JOptionPane.showMessageDialog(THIS,
"The chosen class does not conform to the "Agent" class.");
}
return agent;
}
然而，当这个方法被调用时，我实际上得到了一个NoClassDefFoundError，它被我的catch-all Exception捕获：
Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: TestAgents/TestDFSAgent (wrong name: WumpusEnvironment/Model/Agent/TestAgents/TestDFSAgent)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at WumpusEnvironment.Model.Agent.AgentLoader.loadAgentFromFile(AgentLoader.java:41)
at WumpusEnvironment.View.MainWindow.ApplicationWindow.actionPerformed(ApplicationWindow.java:270)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
我看过以前的同类答案，最初我的.class文件位于整个包结构之外，所以我移动了它们。我的类文件现在和源文件在同一个文件夹中，但我仍然收到这个错误。可能需要注意的是，我正试图在Eclipse中运行这一点，尽管将来整个项目将导出到一个.jar文件中，该文件将实例化不在包结构中的类（因为此时这些都在.jar中）。
有人能在这里给我指正确的方向吗？当我导出到.jar文件时，我也很感激关于如何使您的建议继续有效的建议。我意识到，Eclipse相对于.java文件设置一些.class文件的方式有时会把这些事情搞砸。
谢谢！
有人能在这里给我指正确的方向吗？
我认为正确的方向是不要这样做。我建议你：
-
将插件代理类放入JAR文件中（在JAR中使用正确的路径）。
-
为每个JAR文件创建单独的类加载器，或者为所有JAR文件创建一个类加载器。。。这取决于代理类是否需要彼此隔离。
您遇到的异常是因为classes包名称与classloader根目录中".class"文件的路径不匹配。在最坏的情况下，你无法匹配。。。而不需要移动".class"文件，也不需要编写一个自定义的类加载器来执行一些棘手的操作。即便如此，在处理对其他".class"文件的需要或不需要的依赖关系时，您也会遇到（潜在的）问题。
将插件放入JAR可以避免这些问题。