Decompile an APK, modify it and then recompile it

I need to modify an existing APK, modify the sources and then recompile it.

• I can decompile it using dex2jar or apktool, it's working great
• From the jar file I can obtain the java sources (using jd-gui)
• Then I can modify the java files

But now I would like to know how to recompile the java files and put them back into a jar file! (the jar part should be easy, the main problem seems to be how to recompile the java files for android)

I know that an other solution is to use apktool and then modify the smali files, but it seems to be really complicated when we want to add a lot of code!

My application is a basic a HelloWorld whitout obfuscation.

Thanks to Chris Jester-Young I managed to make it work!

I think the way I managed to do it will work only on really simple projects:

• With Dex2jar I obtained the Jar.
• With jd-gui I convert my Jar back to Java files.

• With apktool i got the android manifest and the resources files.

• In Eclipse I create a new project with the same settings as the old one (checking all the information in the manifest file)

• When the project is created I'm replacing all the resources and the manifest with the ones I obtained with apktool
• I paste the java files I extracted from the Jar in the src folder (respecting the packages)
• I modify those files with what I need
• Everything is compiling!

/!\ be sure you removed the old apk from the device an error will be thrown stating that the apk signature is not the same as the old one!