如何使用 Java 加载插件类？

Question

我制作了一个小应用程序，它从文件夹加载类，将它们显示在列表中，当您单击其中一个时，它会在其中显示 JPanel。

所以我创建了一个扩展 JPanel 的 API 类 (BaseApp)。我还创建了一个测试类 extends BaseApp 并使用其中的 API。

现在，我的问题是每次我点击TestApp，它都会给我这个Exception...

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.Class     cannot be cast to me.Delocaz.SuperApp.BaseApp
at me.Delocaz.SuperApp.AppSelect$2.mouseClicked(AppSelect.java:76)
at java.awt.AWTEventMulticaster.mouseClicked(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$000(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)

我尝试将我从类加载器中获得的Class 转换为BaseApp。我该怎么做才不会崩溃？

如果你需要，这里是我的FileClassLoader：

package me.Delocaz.SuperApp;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class FileClassLoader extends ClassLoader {
    public Class<?> findClass(File f) {
        byte[] b = loadClassData(f);
        try {
        return defineClass(null, b, 0, b.length);
        } catch (ClassFormatError ex) {
        return null;
        }
    }
    private byte[] loadClassData(File f) {
        FileInputStream fin;
        byte fileContent[] = new byte[(int)f.length()];
        try {
            fin = new FileInputStream(f);
            fin.read(fileContent);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return fileContent;
    }
}

此外，这也是强制转换发生的地方：

Object c = cl.findClass(new File(***CLASS FILE LOCATION***));
System.out.println(c);
switchApp((BaseApp) c);

Answer 1

Class 类型的实例不是BaseApp 类型的实例，因此转换失败。您需要实例化该类以获得BaseClass 类型的实例，然后您可以对其进行强制转换

尝试在类实例上调用newInstance() 以获取已加载类的新实例（基于其默认构造函数）