Maven compilation issue with Java 9

Question

Trying to compile a Maven project using JDK 9.0.1 I\'m facing this stacktrace without much of an explanation:

Exception in thread \"main\" java.lang.Assertio         


        

Answer 1

UPDATE

Most of the time this error seems to occur, when the compiler is trying to report a compilation error, but it blows up in the process. So far mainly two approach helped to resolve these issues:

• Disable annotation processing by using -proc:none compiler argument (it seems like that annotation processing can upset the compiler, so if you are not meant to use any, this is a free win).
• Debug the compiler using a conditional breakpoint and walk the stack until a compiler error message can be found, and then fix that error...

ORGINAL SOLUTION

After lots of trial and error I was able to work around/fix this problem locally, my approach in the end was the following:

• I had an assumption that maybe the dependencies are somehow interfering with the build result, so I started to comment out Maven entries in the failing module's POM.
• the build then started to fail, but it did so with the expected cannot find symbol and similar compilation errors instead of the unhelpful AssertionError failure
• it turned out that there was one particular dependency that triggered this AssertionError.
• After code analysis, I couldn't determine any good reason why that dependency would cause problems, so I started to look at the transitive dependencies
• I then used the same approach as before, but instead of uncommenting the faulty dependency, I've inserted all of its transitive dependencies into the POM
• the build again failed, and after lots and lots of testing it turned out that I could trigger the AssertionError when both io.vavr:vavr:0.9.0:compile and javax.servlet:servlet-api:3.0.1:test were included in the dependency graph

It is still beyond me how a test scoped dependency could have any effect on the project's compilation... It also turned out that javax.servlet:servlet-api:3.0.1:provided was already amongst the dependencies of the failing module, and the test scoped dependency wasn't actually used for anything.

In the end I just removed the incorrectly defined test scoped servlet-api dependency from the bug triggering module and suddenly Maven was able to compile the previously failing module.

I'm fairly sure that this is a very obscure answer to a very obscure question in the first place, but hopefully my approach will be of use for someone else.