The project structure is as follows:

parent:

<modules>
  <module>child1</module>
  <module>child2</module>
</modules>

child1:

<modules>
  <module>project1</module>
  <module>project1-1</module>
</modules>

child2:

<modules>
  <module>project2</module>
  <module>project2-1</module>
</modules>

I have two questions:

1. The code for project1 and project1-1 is almost identical, with only dependencies and a few code changes for different runtime environments.
   I am currently copying the code from project1 exactly to project1-1 with a few modifications, but this makes it a bit of a hassle for me to subsequently maintain (two copies of the code need to be maintained when new features are added). Is there a more reasonable way to do this?

2. Also when compiling with maven, sometimes I want to compile only project1 in child1 and project2 in child2. Sometimes I want to compile only project1-1 in child1 and project2-1 in child2. I would like to be able to manage the compilation changes through a profile, but since the module definitions are spread across multiple poms, how should the profile be written?