org.hamcrest isNotNullValue(): which to import when multiple dependencies coexist

Question

I have a dependency coexistence here: isNotNullValue() method exists in different jars in my Spring Boot application and this picture shows what I get for now:

As you can see, I have:

• wiremock.org.hamcrest.core.IsNull
• wiremock.org.hamcrest.CoreMatchers
• org.hamcrest.core.IsNull
• org.hamcrest.Matchers
• org.hamcrest.CoreMatchers

Which one should I import?

I guess hamcrest-library is the right jar, but I am not sure.

Some guidelines to follow when:

• same method exists simultaneously in several jars, while some should be shadowed but not(like in wiremock.org.hamcrest)
• same method exists in several different jars of same dependency, as in hamcrest-core and hamcrest-library

?

Answer 1

Among all the hamcrest suggestions, the one that I almost always end up using is from org.hamcrest.CoreMatchers. Both for isNull and is methods.

The reason you see a similar class hierarchy is because wiremock library has shaded a compatible version of hamcrest along with them. Sometimes you build a library that depends on specific version of dependencies but the users might have a different version of that library which may not be compatible with yours. While code might compile things might fail at Runtime while running them. This can happen with most widely used libraries like Guava (in elasticsearch), and in your case hamcrest (in wiremock). The solution to that problem is to shade the version of your dependencies along with a different package name so they don't cause conflicts or runtime issues for the users. The trade off is your artifact becomes slightly heavier since they also contain your dependencies.