如何在不访问源代码的情况下从现有 Java 应用程序中检索实时数据？

Question

Update: Jun 10, 2022

I have successfully been able to create a demo application with AspectJ integration that could extract variables from the demo application. It was quite a hassle since there's a bit of trouble going on with Eclipse AJDT integration.

I was able to use CLI Java and ajc (AspectJ compiler) to achieve binary weaving into my demo application.

Original Question:

I am trying to retrieve real-time data from a running Java application and push it into an API I have on a server.|

I have no access to the source code of the running application; I only have the Jar file. I have tried decompilation into .java files; however, due to the scale of the app, I was not able to fix all of the missing access$000 function calls.

Is there a certain approach I should use when retrieving real-time data from an existing Java application? Has that been done before? Am I missing something that I am not aware of?

Any help is appreciated.

Answer 1

This is big challenge obviously. If you can glean enough understanding of how the program works from decompiling and reading log files to target some methods where you suspect there's data of interest to your API, then I would read up about Aspect Oriented Programming [AOP] and use those tools.

With AOP you can modify the classes in the jar file at runtime as its loaded by the JVM and access the classes.

For example: You can gather data from:

1. fields within the class that owns a method
2. parameters passed to a method
3. value returned from a method

Once you gather the data, you can also insert calls to your API.

Here's a place to start - https://www.baeldung.com/aspectj .