Abstract
Using Android application, user may sometime have curiosity against basis of output, and drives to know structure of application logic and its processing.
Thank to open source, such desires are fulfilled easily, but it is not always satisfied. As an application distributed from app stores, all Android application is not always distributed as open source.
This post introduces how to explore inside Android application (apk file) to some extent.
Assumption
This post doesn't introduce how to get apk file.
Explore application structure
Creating new project in Android Studio, and opening apk file can accomplish a this purpose. This is also the way introduced at Android developers*2.
Build > Analyze apk...
Although followings items as XML files, images, fonts, and inside of dex file are visible in this way, processing structure is not. Next step is required for more.
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Explore processing structure
To see processing structure inside of application, its steps would be
| Task | Tool |
|---|---|
| Unzip apl file Take dex file Convert dex file to jar file Unzip jar file |
dex2jar*3 |
| Check the contents of jar file | JD-GUI*4 |
| Convert class file to java file | Jad*5 |
Both dex2jar and Jad are command-line tool. Assuming that both are stored at certain folders with appropriate path settings, and refer and output files to following paths
| folder stored apk file | d:\work\20221126\MyApplication.apk |
| output from converting apk | d:\work\20221126\output\ |
| output from converting class file | d:\work\20221126\jad\ |
dex2jar command woul be
.\d2j-dex2jar.bat -o "d:\work\20221126\output\" "d:\work\20221126\MyApplication.apk"
Contents of apk files are automatically converted as apk→dex→jar. And jar file is automatically unzip and deployed its contents to a designated folder.
Rummage about in the folder, make an educated guess at adequate class file. Them, run JD-GUI and open this class file, structure of application is automatically output. The attached image at the top of this post is its screenshot. Needless to say, inside of class file can be seen, too.
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Search related keyword (Search string) to close expected process.
Search > Search...
With checking "Search For" items in advance, return results in each key press. And check process including expected keyword when class file including expected keyword.
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Aditionaly, converting class file to java file with Jad. The next command reproduces the original folder structure under the designated folder, and "MyApplication.java" is output to the corresponding folder.
.\jad -o -r -sjava -d 'D:\work\20221126\jad\' 'D:\work\20221126\output\com\ataraxianstudios\drminfo\activity\MyApplication.class'
