Note: All of the following instructions apply universally (aka to all OSes) unless otherwise specified.

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Prerequsites

You will need:

• A working Java installation
• A working terminal/command prompt
• A computer
• An APK file

Steps

Step 1: Changing the file extension of the APK file

1. Change the file extension of the .apk file by either adding a .zip extension to the filename, or to change .apk to .zip.

   For example, com.example.apk becomes com.example.zip, or com.example.apk.zip. Note that on Windows and macOS, it may prompt you whether you are sure you want to change the file extension. Click OK or Add if you’re using macOS:

Step 2: Extracting Java files from APK

1. Extract the renamed APK file in a specific folder. For example, let that folder be demofolder.

   • If it didn’t work, try opening the file in another application such as WinZip or 7-Zip.

   • For macOS, you can try running unzip in Terminal (available at /Applications/Terminal.app), where it takes one or more arguments: the file to unzip + optional arguments. See man unzip for documentation and arguments.

2. Download dex2jar (see all releases on GitHub) and extract that zip file in the same folder as stated in the previous point.

3. Open command prompt (or a terminal) and change your current directory to the folder created in the previous point and type the command d2j-dex2jar.bat classes.dex and press enter. This will generate classes-dex2jar.jar file in the same folder.

   • macOS/Linux users: Replace d2j-dex2jar.bat with d2j-dex2jar.sh. In other words, run d2j-jar2dex.sh classes.dex in the terminal and press enter.

4. Download Java Decompiler (see all releases on Github) and extract it and start (aka double click) the executable/application.

5. From the JD-GUI window, either drag and drop the generated classes-dex2jar.jar file into it, or go to File > Open File... and browse for the jar.

6. Next, in the menu, go to File > Save All Sources (Windows: Ctrl+Alt+S, macOS: ⌘+⌥+S). This should open a dialog asking you where to save a zip file named `classes-dex2jar.jar.src.zip” consisting of all packages and java files. (You can rename the zip file to be saved)

7. Extract that zip file (classes-dex2jar.jar.src.zip) and you should get all java files of the application.

Step 3: Getting xml files from APK

• For more info, see the apktool website for installation instructions and more

• Windows:

  1. Download the wrapper script (optional) and the apktool jar (required) and place it in the same folder (for example, myxmlfolder).
  2. Change your current directory to the myxmlfolder folder and rename the apktool jar file to apktool.jar.
  3. Place the .apk file in the same folder (i.e myxmlfolder).

  4. Open the command prompt (or terminal) and change your current directory to the folder where apktool is stored (in this case, myxmlfolder). Next, type the command apktool if framework-res.apk.

     What we’re doing here is that we are installing a framework. For more info, see the docs.

  5. The above command should result in “Framework installed …”

  6. In the command prompt, type the command apktool d filename.apk (where filename is the name of apk file). This should decode the file. For more info, see the docs.

     This should result in a folder filename.out being outputted, where filename is the original name of the apk file without the .apk file extension. In this folder are all the XML files such as layout, drawables etc.

Source: How to get source code from APK file – Comptech Blogspot