How to load a class from a .jar Android

Question

I have this code. I manually add the rectanglecalcul.jar in the folder data/data/com.xxx.xxx/files and the Log confirms file exist is true. This is the second part of my project, in the first part, I tried to download the JAR file from my server (it is not working yet that's why I add it by my self in the AVD).

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();
            }

It is actually working on a Java project, but when I try on an Android project, a NullPointerExecption appears when I call the method loadclass.

I tried to add READ & WRITE permissions on External and Internal storage but it does not help.

Here is the LogCat:

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)

I have spent a lot of time on this, trying a lot of workaround but nothing works. So I need help !

My apologize if there is any english mistakes !

Did you notice the [JarClassLoader](http://docs.oracle.com/javase/tutorial/deployment/jar/jarclassloader.html)? — Christian St., Jul 07 '14 at 16:19

score 2 · Accepted Answer · answered Jul 08 '14 at 15:50

I finally found what i was searching for ! I used dalvik.system.DexClassLoader. Then i have to create the classes.dex.

http://www.herongyang.com/Android/Project-dx-Command-Converting-class-Files-into-dex-File.html

Add classes.dex in the jar and it's working !

Here is my code.

                File f = new File(c.getFilesDir().getPath()
                        + "/calculmobiledex.jar");
                Log.i("File", "" + f.exists());

                DexClassLoader u = new DexClassLoader(f.toURI().toURL()
                        .toString(), c.getDir("libs", c.MODE_PRIVATE)
                        .getAbsolutePath(), null,
                        ClassLoader.getSystemClassLoader());
                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);

                Log.i("method = ", "" + m.invoke(o, 1, 1));
                m = null;

score 1 · Answer 2 · answered Jul 08 '14 at 01:05

1

If you want to load class from .jar (that contains dalvik bytecodes), you should use dalvik.system.PathClassLoader.

See http://developer.android.com/reference/dalvik/system/PathClassLoader.html

answered Jul 08 '14 at 01:05

ganachoco

302
1
3

How to load a class from a .jar Android

2 Answers2