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Asked: 2026-05-13T22:34:56+00:00

I’m refatoring a home-grown DAO container, hoping to make the class generic. It internally

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I’m refatoring a home-grown DAO container, hoping to make the class generic. It internally uses an ArrayList to store the retrieved objects.

One usage of this class puts the container’s list into a request scope, and due to a limitation of Websphere, I can’t pass the generic List<Foo> to the request scope (Websphere doesn’t handle generics out-of-the-box)

If I go ahead with my refactorings, I will need to convert/cast the List<Foo> into a non-generic List object..

// Boils down to this...
List<Foo> listFoo = new FooListing().findAllFoo();
List listThings = listFoo;
request.setAttribute("listThings", listThings);

What are the implications of reversing a generification like this? Should I avoid doing this kind of manipulation?

EDIT: The code snippet is verbose to explicitly demonstrate what I’m describing..

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1 Answer

  1. Editorial Team

    If the component type of the List does match the expected type, there is no problem.

    Generics in Java are only used for type-checks by the compiler, they have not effect at runtime. If you are using an older library that does not support generics, you have no choice but to ignore the generic type.
    Things should continue to work, as this system has been designed with backwards compatibility in mind.

    So all you are losing is the compile-time type checking (it puts you back to where Java was at 1.4, which means, if the types match, everything will work, if not, you’ll get ClassCastExceptions or other unwanted behaviour at runtime).

    However, I think you can just write

    request.setAttribute("listThings", listFoo);

    This method takes any kind of Object. Even if it wanted a List, you could still pass a List<Foo> (which is still a List).

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