Deriving Class from Generic T

java generics reflection derived-class
bowsie picture bowsie · Apr 29, 2009 · Viewed 8.5k times · Source

I have a parameterized hibernate dao that performs basic crud operations, and when parameterized is used as a delegate to fulfil basic crud operations for a given dao.

public class HibernateDao <T, ID extends Serializable> implements GenericDao<T, ID>

I want to be able to derive Class from T at runtime to create criteria queries in Hibernate, such that:

public T findByPrimaryKey(ID id) {
    return (T) HibernateUtil.getSession().load(T.getClass(), id);
}

I know:

T.getClass()

does not exist, but is there any way to derive the correct Class object from T at runtime?

I have looked at generics and reflection but have not come up with a suitable solution, perhaps I am missing something.

Thanks.

Answer

Adam Paynter picture Adam Paynter · Apr 29, 2009

You could have the Class passed as a constructor argument.

public class HibernateDao <T, ID extends Serializable> implements GenericDao<T, ID> {

    private final Class<? extends T> type;

    public HibernateDao(Class<? extends T> type) {
        this.type = type;
    }

    // ....

}

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