Question

I have spent most of a day trying to understand why Java cannot compile a simple generic method with a generic type argument, but only when the enclosing class is imported. Basically, I am exposing a Spring context operation as a static method in a class called SpringApplicationContext:

public static <T> List<T> listBeansOfType(Class<T> type)
{
  return new ArrayList<T>(context.getBeansOfType(type).values());
}

When I call it from a unit test in the same package, it works. Here’s the test call:

 List<DomainRepo> repos =
   SpringApplicationContext.listBeansOfType(DomainRepo.class);

However, the exact same code fails when I call it from code in another package. The compiler says it cannot find the symbol listBeansOfType(java.lang.Class). I have imported the class, but I have not done a static import on the method.

Even stranger is the fact that this code worked a week ago when I wrote it. Since then, I had to put it all aside while working through a release process. The same error occurs when I compile with maven or Eclipse, using java 1.6. Any hints will be more than welcome.

Answer 1

Make sure you have all needed maven dependencies. If your Junit Test works, but mvn compile fails the dependency could be included with scope Test.

    <dependency>
       <groupId>group-a</groupId>
       <artifactId>artifact-b</artifactId>
       <version>1.0</version>
       <scope>TEST</scope> <!-- would explain why you can run your code as junit -->
    </dependency>

Check the type of “context” and where the method getBeansOfType() is defined. They might be missing as mvn dependency.