Adding a user to a Role in all Projects based on a criteria

I am trying to see using Java Code, how I can achive this

I need to add a user lets say "user1" to a Role "Engineering Manager" to all Projects where another user . lets say "user2" is assigned to the Role "Engineeering Manager"

We have arounf 200 Projects, a Java script to achive this will save us a lot of time

Any one can help me with this . I am new to Java ...

Thanks