Decompile an APK, modify it and then recompile it

The answers are already kind of outdated or not complete. This maybe works for non-protected apks (no Proguard), but nowadays nobody deploys an unprotected apk. The way I was able to modify a (my) well-protected apk (Proguard, security check which checks for "hacking tools", security check, which checks if the app is repackaged with debug mode,...) is via apktool as already mentioned by other ones here. But nobody explained, that you have to sign the app again.

apktool d app.apk
//generates a folder with smali bytecode files. 

//Do something with it.

apktool b [folder name] -o modified.apk
//generates the modified apk.

//and then
jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore ~/.android/debug.keystore modified.apk androiddebugkey
//signs the app the the debug key (the password is android)

//this apk can be installed on a device.

In my test, the original release apk had no logging. After I decompiled with apktool I exchanged a full byte code file without logging by a full byte code file with logging, re-compiled and signed it and I was able to install it on my device. Afterwards I was able to see the logs in Android Studio as I connected the app to it.

In my opinion, decompiling with dex2jar and JD-GUI is only helpful to get a better understanding what the classes are doing, just for reading purposes. But since everything is proguarded, I'm not sure that you can ever re-compile this half-baked Java code to a working apk. If so, please let me know. I think, the only way is to manipulate the byte code itself as mentioned in this example.

1. First download the dex2jar tool from Following link http://code.google.com/p/dex2jar/downloads/list

2. Extract the file it create dex2jar folder

3. Now you pick your apk file and change its extension .apk to .zip after changing extension it seems to be zip file then extract this zip file you found classes.dex file

4. Now pick classes.dex file and put it into dex2jar folder

5. Now open cmd window and type the path of dex2jar folder

6. Now type the command dex2jar.bat classes.dex and press Enter

7. Now Open the dex2jar folder you found classes_dex2jar.jar file

8. Next you download the java decompiler tool from the following link http://java.decompiler.free.fr/?q=jdgui

9. Last Step Open the file classes_dex2jar.jar in java decompiler tool now you can see apk code

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!

I know this question is answered still, I would like to pass an information how to get source code from apk with out dexjar.

There is an online decompiler for android apks

1. Upload apk from local machine
2. Wait some moments
3. Download source code in zip format

I don't know how reliable is this.

@darkheir Answer is the manual way to do decompile apk. It helps us to understand different phases in Apk creation.

Once you have source code , follow the step mentioned in the accepted answer

Report so many ads on this links Another online Apk De-compiler @Andrew Rukin : http://www.javadecompilers.com/apk

Still worth. Hats Off to creators.