Using Java generics for JPA findAll() query with WHERE clause

Question

So, After a 10+ year break I\'m coming back to Java and trying out stuff with JPA and Java generics. I\'ve created a generics based findAll(other) JPA query tha

Answer 1

I found this page very useful

https://code.google.com/p/spring-finance-manager/source/browse/trunk/src/main/java/net/stsmedia/financemanager/dao/GenericDAOWithJPA.java?r=2

public abstract class GenericDAOWithJPA {

    private Class persistentClass;

    //This you might want to get injected by the container
    protected EntityManager entityManager;

    @SuppressWarnings("unchecked")
    public GenericDAOWithJPA() {
            this.persistentClass = (Class) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }

    @SuppressWarnings("unchecked")
    public List findAll() {
            return entityManager.createQuery("Select t from " + persistentClass.getSimpleName() + " t").getResultList();
    }
}