1

When packaging Java projects we rely on Maven, but I assume the problems are the same with Gradle or Ant. Sometimes we run into the problem known as "Jar Hell" if one dependency relies on a transitive dependency in a different version than another dependency, guava as an often occurring example. If the loaded library has conflicting classpaths or function signatures you get the infamous ClassNotFoundException or NoSuchMethodError at runtime. ("funny" that one is an Exception and the other an Error btw^^)

I know that the problems can be somewhat solved with dependencyManagement, using the Maven Shade Plugin and detected using the Enforcer Plugin with e.g. "Dependency Convergence". I am also aware of the many questions related to these methods as e.g. SO Link.

Now my question is how can we detect these errors at compile time? As I understand the java compiler javac itself doesn't really have mechanisms for packaging applications itself, but I would assume that a jar packager such as shade, assembly or the like would be able to detect if all classes and methods are present? Obviously assuming that no classes will be loaded at runtime. (Which is the case for us as we mainly build stand-alone applications and don't deal with application servers such as JBoss/Wildfly)

Maximilian Schulz
  • 392
  • 3
  • 12
  • 1
    Simple answer. You can not. The only solution would be having good test suite with a very good coverage. The first best practice is: If you are using classes from an transitive dependency make them to your own dependency and don't rely on transitive dependencies. Furthermore it is not related to packaging cause how should the packaging being able to identify a missing class/method? For example what about reflection/dependency injection etc... so the only solution is having enough tests which cover all things. – khmarbaise Dec 11 '18 at 09:28
  • 1
    You can cause some of these problems to fail fast, at program start up, using the modules feature introduced in Java 9. – Raedwald Dec 11 '18 at 09:45
  • If you start up the application it's too late..it should be found before startup which means at build time (using tests)... – khmarbaise Dec 11 '18 at 09:57
  • We try to avoid dependency injection that cant be checked by a compiler/packager and emulate the behavior of a compiled application e.g. like in C++ with only static libraries, surely this should be possible? I don't see what's the inherent difference between "direct" and transitive dependencies for the build step. Of course, 100% Test coverage is a nice goal but not an answer to the question :-) Modules Feature introduced in Java 9 we are looking into, fail fast is definitely better - even better would be at compile time. – Maximilian Schulz Dec 11 '18 at 16:51

0 Answers0