java - custom class loader for android?

Question

I'm writing an instrumentation library that I'd like to work on both desktop and mobile (Android).

It functions by:

1. Exposing a main which takes a single parameter, the main of the target class
2. Installing a class loader which intercepts all classes as they are loaded and instruments them

Like so:

    // Expects args[0] to contain the name of the INNER main
    public static void main(String[] args) throws Throwable {
            String className = args[0];
            String [] newArgs = new String[0];

            if(args.length > 1) {
                    newArgs = Arrays.copyOfRange(args, 1, args.length-1);
            }

            System.out.println("Bootstrapping " + className);

            Loader s = new Loader(ClassLoader.getSystemClassLoader().getParent());
            Class<?> c = s.loadClass(className);
            c.getDeclaredMethod("main", new Class[] { String[].class }).invoke(
                            null, new Object[] { newArgs });
    }

The question is this:

How can I do roughly the same thing for an android app?

One idea is to modify the android manifest to replace the existing activities with "wrapper" activities, that then install class loaders and call into the original underlying activity. Is there a better way?

Answer 1

There is a project called droidbox to detect android malware. There is a code that can help you a lot.

package com.loader;

import dalvik.system.DexClassLoader;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;

public class LoaderActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        DexClassLoader dLoader = new DexClassLoader("/sdcard/DroidBoxTests.apk","/sdcard/", null, ClassLoader.getSystemClassLoader().getParent());

        Class calledClass = null;
        try {
            calledClass = dLoader.loadClass("droidbox.tests.DroidBoxTests");
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        Intent it=new Intent(this, calledClass);
        it.setClassName("droidbox.tests", "droidbox.tests.DroidBoxTests");
        startActivity(it);
    }
}