Incompatible types, equality constraints and method not found during Java 9 Migration

Question

While migrating one of our projects to Java 9(build 9+181), I am facing a peculiar problem what looks like an incorrect implementation in some libr

Answer 1

From the sample project I was able to fix the compilation issue. There were 2 exceptions in com.SomeService#run method. There were missing modules in your module-info.java, once you add these the code should compile.

requires dropwizard.jersey;
requires dropwizard.jetty;

JerseyEnvironment comes from io.dropwizard:dropwizard-jersey:1.1.0

ServletEnvironment comes from io.dropwizard:dropwizard-jetty:1.1.0

Since they are different jars, they export different modules. Hence, the requires needs to be explicitly added. Your code works fine without module-info.java because at that time module system is not used.

I found the fix by doing the below, method mentioned in comments:

@Override
public void run(SomeServiceConfig config, Environment environment) throws Exception {
    Injector injector = Guice.createInjector(new SomeServiceModule());
    // Fix: Extract to variable to find Type of jersey and then find the module to add under requires
    JerseyEnvironment jersey = environment.jersey(); 
    jersey.register(injector.getInstance(SomeResource.class));
    // Fix 2: Same method as Fix 1
    ServletEnvironment servlets = environment.servlets();
    servlets.addFilter("Some-Filter", SomeFilter.class);
}