我有這段代碼。 我手動添加文件夾data/data/com.xxx.xxx /文件中的rectanglecalcul.jar,並且日誌確認文件存在爲true。這是我項目的第二部分,在第一部分中,我嘗試從我的服務器上下載JAR文件(它還沒有工作,這就是爲什麼我自己將它添加到AVD中)。如何從.jar載入一個類Android
try {
File f = new File(c.getFilesDir().getPath()
+ "/rectanglecalcul.jar");
Log.i("File", "" + f.exists());
URLClassLoader u = new URLClassLoader(new URL[] { f.toURI()
.toURL() });
Class<?> c = u.loadClass("perimetre.calcul");
Constructor<?> constru = c.getConstructor(int.class,
int.class);
Object o = constru.newInstance(2, 2);
Method m = c.getMethod("resultat", int.class, int.class);
m.setAccessible(true);
m = null;
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SecurityException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (NoSuchMethodException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InstantiationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
它實際上是工作的一個Java項目,但當我嘗試在Android項目,當我打電話loadClass方法出現NullPointerExecption。
我試圖在外部和內部存儲上添加READ & WRITE權限,但它沒有幫助。
這裏是logcat的:
07-07 06:57:07.644: E/AndroidRuntime(11385): java.lang.NullPointerException
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.net.URLClassLoader.getPermissions(URLClassLoader.java:614)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.security.SecureClassLoader.getPD(SecureClassLoader.java:140)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:93)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.net.URLClassLoader.access$600(URLClassLoader.java:55)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.net.URLClassLoader$URLJarHandler.createClass(URLClassLoader.java:364)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.net.URLClassLoader$URLJarHandler.findClass(URLClassLoader.java:303)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.net.URLClassLoader.findClass(URLClassLoader.java:748)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.lang.ClassLoader.loadClass(ClassLoader.java:497)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.lang.ClassLoader.loadClass(ClassLoader.java:457)
07-07 06:57:07.644: E/AndroidRuntime(11385): at com.example.androidimportjar.MainActivity$1.onClick(MainActivity.java:79)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.view.View.performClick(View.java:4438)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.view.View$PerformClick.run(View.java:18422)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.os.Handler.handleCallback(Handler.java:733)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.os.Handler.dispatchMessage(Handler.java:95)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.os.Looper.loop(Looper.java:136)
07-07 06:57:07.644: E/AndroidRuntime(11385): at android.app.ActivityThread.main(ActivityThread.java:5017)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.lang.reflect.Method.invokeNative(Native Method)
07-07 06:57:07.644: E/AndroidRuntime(11385): at java.lang.reflect.Method.invoke(Method.java:515)
07-07 06:57:07.644: E/AndroidRuntime(11385): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
07-07 06:57:07.644: E/AndroidRuntime(11385): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
07-07 06:57:07.644: E/AndroidRuntime(11385): at dalvik.system.NativeStart.main(Native Method)
我已經花了這個有很多的時間,嘗試了很多解決辦法,但沒有任何工程。 所以我需要幫助!
如果有任何英文錯誤,我很抱歉!
您是否注意到[JarClassLoader](http://docs.oracle.com/javase/tutorial/deployment/jar/jarclassloader.html)? –