如何使用Java加載插件類？

Question

我創建了一個小應用程序，它從一個文件夾中加載類，將它們顯示在一個列表中，當你點擊它時，它會在其中顯示JPanel 。

所以我創建了一個擴展JPanel的API類（ BaseApp ）。 我還創建了一個測試類，它extends BaseApp並使用了API。

現在，我的問題是，每次我點擊TestApp ，它都會給我這個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)

我曾試圖投的Class從我的類加載器我陷入了BaseApp 。 如果沒有它崩潰，我該怎么做？

如果你需要它，這是我的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，這是鑄造發生的地方：

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

Answer 1

類型Class的實例不是BaseApp類型的實例，因此轉換失敗。 您需要實例化該類以獲取BaseClass類型的實例，然后您可以將其強制轉換

嘗試在類實例上調用newInstance()以獲取已加載類的新實例（基於其默認構造函數）