How to add external java library to custom Android framework?

Can someone enlighten me on how to include an external java framework to android framework and compile it as a part of the custom android framework?

The idea is to make this external framework a part of my custom android framework and expose it as android service for other processes to use.

In essence what I did is -

checked for android port of the java framework
Copied the src dir (including all the external jar files) from the ported framework to framework/base/core/java/android/
Edited ActivityManager in the framework to call the copied library
run make

Is this the right approach to edit Android framework? Since, I am including the java files and associated external jars of the external project inside the Android framework I suspect make fails while converting the jars to dex.

Can somebody point me towards any available resources dealing with Android Framework internals and on how to edit Android framework?

I checked the Tutorial: Android Internals - Building a Custom ROM, Pt. 2 of 2 on youtube from this year's Marko Gargenta presentation in Beijing, China. But he didn't make it (i.e. adding external framework or jars) clear either.

Solution

First: I'm not very experienced in the Android build process, so there might be a better solution, but this one should work (at least for Android 2.2).

I assume, that you use Eclipse for the source code modification and already executed a successful make -j4...

Create a new source folder: external/<your-library>/src
Copy all Java source files into this folder.
Open the following make file: <android>/frameworks/base/Android.mk

Search for # Build ext.jar and add your library as follows:

[...]
ext_dirs := \
    ../../external/apache-http/src \
    ../../external/<your-library>/src \
    ../../external/gdata/src \
    ../../external/protobuf/src \
    ../../external/tagsoup/src
[...]

Now you should be able to access these libraries from the Android framework...
Finally execute make -j4 ext to build only the external module,
Or make -j4 to build all changed files (if a previous build exists in /out/).