处理maven多模块项目中的相互依赖

Question

I'm been going through the Maven Framework . While going through multi-module projects, I read that cyclic dependency is not acceptable among the modules. So I thought of a scenario, something like...

   root ----------
    - pom.xml    |
                 |
                 |--- moduleA
                 |  - pom.xml (moduleB has been added as a dependancy)
                 |
                 |--- moduleB
                    - pom.xml
                    
                    

Assume that moduleA has a property class AppProperty and a Main class which invokes another class B available in moduleB

Main class available in moduleA :-

someValue = AppProperty.get(propKey);

    //some logic
    
B mb = new B();
B.process(...);

Class B of moduleB :-

process(...) {
someOtherValue = AppProperty.get(someKey)

    // some other logic
}

Now Main will not throw any compile-time errors as its dependancies have been resolved because moduleB has been added as a dependancy in moduleA'a pom.xml . But for class B that is not the case as its invoking AppProperty class which is available in moduleA only. I cannot add moduleA 's dependancy in moduleB 's pom as that would lead to cyclic dependancy (if I understand it correctly).

I understand that ideally it is advised to maintain codes in an acyclic manner, but what if because of some reason removing cyclic dependancy is just not feasible? In such a scenario, is there any way to handle cyclic dependancies without actively changing the existing code logic ?

Answer 1

You cannot build a project with cyclic dependencies. You need to build B before A before B, which is kind of a contradiction.

But problems like yours are easy to solve:

• If the problem is just the class AppProperty or a few others, just move them from A to B.
• If you have some common classes for A and B, create a helper module C and use it as dependency in A and B.
• If A and B call each other all of the time, they should probably be just one module. So merge them to one module.