How To Use Android Internal APIs

    When I was working on this demo(exercise, actually), I want to use the ServiceManager java class(which is hidden in Android SDK) since the demo is aim to build a simple native service which has a role like the system_server ( accessing some crucial system parts like hardware )except that it isn't live in the system_server process. So neither the bindService routine, which is designed for "App Service", nor the getService method, which is created for the services live in system_server, will work.

    Here are the steps:

1. We need to build the AOSP, at least some specific framework parts, which located mostly in framework/base. You can go there and invoked the mma or mm command to build the module instead of the whole Android system.
      
2. Assume your output dir is out, then go to out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/, copy the classes.jar to ${YOUR_SDK_DIR}/platforms/android-${YOUR_API_LEVEL}/ .
      
3. In the dir ${YOUR_SDK_DIR}/platforms/android-${YOUR_API_LEVEL}, unpack both the classes.jar we've just copy and the android.jar since a jar file is simply an archive file.
      
4. This step depends on your need. Since I only wants the ServiceManager class, I only have to copy content in the android folder in the output of the classes.jar, which holds the android.* classes we normally seen in the java import statements, into the corresponding android folder in the output of the android.jar. By doing this, you can still keep some libraries like dalvik.* in the origin SDK but not exist in the AOSP framework part.
      
5. Change dir to the modified android.jar output dir. Repack them using the command:
   jar -cf ./your_new_android.jar *
   Remember to cascade your new android.jar file path RIGHT AFTER the -f option.
      
6. Then you will got the new android.jar which can used in the App development. I also kept the original android.jar and wrote a simple script to switch between the origin one and the "Hacked" one:
   

   #!/bin/bash
   
   USAGE="Usage: ${0} <aosp|sdk>"
   
   case "$1" in 
   "aosp") ln -sf android_aosp.jar android.jar
    ;;
   
   "sdk") ln -sf android_sdk_origin.jar android.jar
    ;;
   *) echo $USAGE
    ;;
   
   esac
   
   exit 0
   

    In the old Eclipse era, we can add the new android.jar to the build path and raise the priority among the dependency libraries. However, since Android Studio is highly integrated with Android SDK, we can't modify the actual SDK files in the IDE.