@Service
public abstract class MainService<E extends AbstractEntity, R extends MainRepository<E>> {
@Autowired
MainRepository<E> repository;
public E find(long id) throws Exception {
return this.repository.find(---, id);
}
}
Here is it possible to find the class reference of the generic type E to pass through this method as first argument instead of the --- ...?
My expectation about the implementation is to create a generic call to avoid the repetition of the below code in all service classes.
return this.repository.find(Entity.class,id);
Yes, here's an example of doing that:
import java.lang.reflect.ParameterizedType;
public class Foo {
public static abstract class Bar<E> {
public E returnAnE() throws InstantiationException, IllegalAccessException {
Class e = (Class)((ParameterizedType)this.getClass().getGenericSuperclass()).getActualTypeArguments()[0];
return (E)e.newInstance();
}
}
public static class Baz extends Bar<String> {
}
public static void main(String[] args) throws InstantiationException, IllegalAccessException {
Baz baz = new Baz();
String s = baz.returnAnE();
}
}
This code will fail with class structures which don't match what we have here, so you should do instance of checks instead of casts, and check array accesses.