Decompile an APK modify it and then recompile it

Question

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

User · Answer

I know this question has been answered and I am not trying to give better answer here. I'll just share my experience in this topic.

Once I lost my code and I had the apk file only. I decompiled it using the tool below and it made my day.

These tools MUST be used in such situation, otherwise, it is unethical and even sometimes it is illegal, (stealing somebody else's effort). So please use it wisely.

Those are my favorite tools for doing that:

javadecompilers.com

and to get the apk from google play you can google it or check out those sites:

On the date of posting this answer I tested all the links and it worked perfect for me.

NOTE: Apk Decompiling is not effective in case of proguarded code. Because Proguard shrink and obfuscates the code and rename classes to nonsense names which make it fairly hard to understand the code.

Bonus:

Basic tutorial of Using Proguard:

User · Answer

This is a way   Using apktool to decode     apktool d -f  apkfile  -o  output folder    Next  using JADX  at github com skylot jadx     jadx -d  output folder   apkfile     2 tools extract and decompiler to same output folder  Easy way  Using Online APK Decompiler  https   apk tools tools apk-decompiler   recommended  http   www javadecompilers com apk https   www apkdecompilers com

User · Answer

dex2jar with jd-gui will give all the java source files but they are not exactly the same  They are almost equivalent  class files  not 100    So if you want to change the code for an apk file     decompile using apktool apktool will generate smali Assembly version of dex  file for every java file with same name  smali is human understandable  make changes in the relevant file  recompile using same apktool apktool b Nw apk  lt Folder Containing Modified Files gt

User · Answer

I know this question is answered still and I am not trying to be smart here  I ll just want to share another method on this topic   Download applications with apk grail  APK Grail providing the free zip file of the application

User · Answer

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  Upload apk from local machine Wait some moments 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

User · Answer

First download the dex2jar tool from Following link       http   code google com p dex2jar downloads list Extract the file it create dex2jar folder 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 Now pick classes dex file and put it into dex2jar folder Now open cmd window and type the path of dex2jar folder Now type the command dex2jar bat classes dex and  press Enter  Now Open the dex2jar folder you found  classes dex2jar jar file Next you download the java decompiler tool from the following link http   java decompiler free fr  q jdgui Last Step Open the file classes dex2jar jar in java decompiler tool  now you can see apk code

User · Answer

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

User · Answer

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

[java] Decompile an APK, modify it and then recompile it

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