Do newer versions of dependencies override older versions in maven projects?

Question

If I have a maven project which has explicit dependencies on A and B version 2.0 and A has transitive dependency on B version 1.0. Does newer version of B override older version? I used maven depencdy:resolve goal and it looks like older version of B is not resolved. What if A is incompatible with newer version of B? Or if A depends on B version 2.0 and my project has explicit dependency on B version 1.0 after running dependency:resolve goal I don't see newer version of B then. So how do these dependencies get resolved then?

And when I use resolve goal it shows dependencies. But what phase this dependencies will be used in? Compile, test, runtime?

Answer 1

The version that is closer to the root of your dependency tree will be preferred. If both conflicting versions have the same depth in the tree, then the first one (starting from the top of the tree) wins.

Is that a completely stupid rule? Yes it is. The only advantage it has is that you can always force a specific version of a dependency by declaring it as a direct dependency of your project.

So in your case, B:2.0 will be used, since it's declared as a direct dependency. If A doesn't work fine with B:2.0, then, well, either use B:1.0 in your code, or choose another library that does the same thing as A but doesn't cause a conflict.

Answer 2

I maven do not choose the newer version of an artifact when multiple versions are referenced in the dependency tree. Looking at http://maven.apache.org/plugins/maven-dependency-plugin/examples/resolving-conflicts-using-the-dependency-tree.html, it seems it chooses the nearest definition from the root of the tree. That means that the version in the main POM will be preferred to the one in transitive dependencies. So if instead, you had your project depends on B v1.0 and A had a transitive dependency on B v2.0, then your project will have chosen B v1.0.