Hello, I needed some help in using `java agent` in...

# android

[rahul_lohra]

Hello, I needed some help in using java agent in Android, basically there is a premain function and I need this function to run before the Android's main function bus I was unsuccessful. So I am looking for some advice, what can go wrong? Also I am not getting anything on the log cat so it very difficult to debug

The is the manifest of the jar

Manifest-Version: 1.0
Premain-Class: com.rahullohra.myagent.MyPremain
Launcher-Agent-Class: com.rahullohra.myagent.MyPremain
Boot-Class-Path: /home/rahulkumarlohra-xps/AndroidStudioProjects/Lab/m
 yagent/build/libs/myagent.jar

In gradle.properties I have passed this jar as

org.gradle.jvmargs=-javaagent:'/home/rahulkumarlohra-xps/AndroidStudioProjects/Lab/myagent/build/libs/myagent.jar'

[Adam Powell]

This doesn't exist in Android. Android app startup happens in a very different way. What are you trying to do? What code do you want to run before other app code at startup and why?

[rahul_lohra]

Hi Adam,
I want this feature to be available only for DEBUG variant

TL;DR - I want to inject bytecode/java code some classes during compile time at specific places. I do not want to use any annotations.

Full story:

What I want & Why: -
Two things
First -
I want to track our image loading performance in our app. Now assume my team is using Glide to load images and lot of people have already written code like below

Glide.with(context).load(url).into(imageView)

Now during compile time I want to attach listener to above code and it will now look like this -

val glideListener = {....some logic...}
Glide.with(context).load(url).addListener(glideListener).into(imageView)

Now I know anyone will say that one should use a common class to load images, so that all the image loading calls will go through there and I totally agree with this. But I just want to explore what are the other possible ways to achieve this thing

Second thing -
I want to avoid exceptions.
So I want to execute some instructions just before my actual content function will start to execute (This is very similar to aspectJ)

[Adam Powell]

A pre-main is by definition runtime as opposed to compile time, you shouldn't need it if you are doing compile-time transformations.

[Adam Powell]

If you do have runtime startup code you might find this useful: https://developer.android.com/topic/libraries/app-startup

[Adam Powell]

but based on your description it sounds like this isn't really what you want either

[rahul_lohra]

Thank you for correcting me Adam regarding compile-time transformations & compile-time transformations. 👍
And yes app-startup will not help me.

Thanks to you, now at least I know where not to look.

[rahul_lohra]

For run-time class transformation - I think I should read on how the Android OS works and starts an application, I think from there I can get some hint

For compile-time transformation - I think if I just write a simple script that will just modify the code the way I want. Then I can get what i want.

Once again thanks a lot Adam👍

[Justin Tullgren]

Hi, I have a couple of suggestions if you want:
1. Use debug/release source sets. Pull the code you want to augment into a top level kotlin function. Declare it in both release and debug source sets but not in the main source set. In the debug add the listener/extra code. The release is the normal code. Then in main call the extracted top level function.
2. If you truly need byte code level you can use AOP byte code weaving using this plugin : https://github.com/Archinamon/android-gradle-aspectj and write aspects for your code in aspect j syntax, no annotations, where you can define your pointcuts. This happens at compile time in during the AGP transform step.

[rahul_lohra]

Thanks Justin, I will try this library