如何在Eclipse中解决循环项目依赖关系。 有什么办法只能使其中一个依赖项运行时吗？

Question

I have a project that basically consists of 2 modules. I have a Eclipse workspace and 2 java projects (maven) in it which represent those two modules.

To go a bit more in depth:

• Project 1 : Core Module (Has Core Implementation and API Interfaces)
• Project 2 : Auxiliary Module (A Server)

Project 2 requires to have Project 1 as Dependency in order to access the API Interfaces during compile time. But the problem is that Project 1 requires Project 2 in order to work properly (This is only a runtime requirement though).

So when I add in each project the other project as dependency a cyclic dependency error is shown, as Eclipse doesn't knows in which order to compile the classes.

The way I managed to make this work is that I added the "bin" folder from Project 2 as dependency to Project 1 as also all of Project 2 dependencies (Which are maven based). This though makes the whole project completely bound to my system, as all paths are adjusted to my computer setup.

Is there any proper way to specify another project to be dependency only on "runtime", and not on "compile" and avoid the cyclic redundancy in Eclipse?

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To explain in a more visual way. What I need is:

• Project 2 --- During compilation depends on ---> Project 1

• Project 1 --- During runtime depends on ---> Project 2

Answer 1

Eclipse can handle circular project dependencies but by default circular dependencies will be reported as an error for good reasons (splitting code into projects with circular dependencies makes no sense).

You can decrease the circular dependencies project problem severity from Error to Warning for both projects as follows (not recommended):

1. In Project > Properties: Java Compiler > Building
   1. check the checkbox Enable project specific settings and
   2. in the section Build path problems choose for Circular dependencies Warning instead of Error

Answer 2

In Maven, dependencies have a scope. They can be declared as "compile", "runtime", "test" etc.

You can declare a compile dependency on Project1 in Project2 and a runtime dependency in Project1 on Project2. I have never tried to define dependencies in such a way, but it will probably work.

But, much more important: If Project1 cannot be used without Project2 and vice versa, why are they different projects?

Answer 3

So based on @JF-Meier's comments, I found another way how to make this work. The whole idea was basically to have Project 2 loosely coupled to Project 1 , to allow Project 2 to be swapped with other implementations, while still being a vital part to Project 1 to work.

To solve the circular dependency issue, I've just created another project that sets Project 1 and Project 2 as it's dependency, and from there I launch Project 1 . This solved the circular dependency issue for me and everything works.

The result:

• Project 0 : Launcher to start Project 1
• Project 1 : Core Module (Has Core Implementation and API Interfaces)
• Project 2 : Auxiliary Module (A Server)

And the dependencies:

• Project 1 --- Depends on nothing

• Project 2 --- Depends on ---> Project 1

• Project 0 --- Depends on ---> Project 1 and Project 2

And like this I can launch Project 1 from Project 0 while having Project 2 on the classpath (So Project 1 can find Project 2 as required).

I marked the response from @howlger as accepted as it also fixed my issue. But in case my question was not well understantable, I'm putting here how I finally fixed it, in case it may be helpfull for somebody else trying to achieve the same like me.

Thanks for all the help as always here!