How to log executed lines of code and variables at that point in Java?

Question

I'm working on a project for my Uni where I want to visualize code debugging. For this I somehow need to log the executed Lines of Code and the variables with their values for a given Java program. An example:

public class Main {

public static void main(String[] args){
   String abc = "def";
   String test = "hello world";
   String foo = abc+test;   
}
}

If i log this programm my output should be something like this:

1. Main at line 3:
2. Main at line 4: abc=def
3. Main at line 5: abc=def,test = hello world
4. Main at line 6: abc=def, test = hello world, foo = defhello world

The logging program should run in the background so I can use the logged program normally. I already tried stuff with Java Agents and Stacktrace but I could'nt get good results. I hope there is any way to do this. Thanks for any help in advance!

Answer 1

There are ways to do this, some IDE like Intelij IDEA actually display the variable value in the editor when you debug.

But if you want to log that, not only the information log would soon become huge (gigabytes/terabytes for real programs) but it would be quite complex.

Here several ways to do this:

• Actually use the debugger API to interract with the running program and so log that information: https://docs.oracle.com/javase/8/docs/technotes/guides/jpda/index.html
• Make it with a plugin to the compiler so it add the necessary logs. I think that was your approach.
• Create a Java => Java compiler that add the matching source and let the standard compiler compile the java. For that there an open source API for eclipse I think that they use for refactoring in the IDE. (Here a blog post that show you can use the API to read java code: https://www.vogella.com/tutorials/EclipseJDT/article.html)