CODEWITHSUNDEEP
javahibernategenericscasting
Dagon
Dagon

Reputation: 155

Method generic return java class

I am building generic methods for queries to the database with Hibernate, the following method consults the information of an entity by primary key.

@PersistenceContext(unitName = "UnitPers")
private EntityManager entity;

public Object findByPk(Class clazz, Object pk) throws Exception {
    Object obj = null;
    try {
        obj = entity().find(clazz, pk);
    } catch (Exception e) {
        throw e;
    }
    return obj;
}

This method works correctly, but I do not want to make a cast (object to myTypeEntity) when making the call.

private myTypeEntity entity;    
entity = (myTypeEntity) findByPk(myTypeEntity.class, new Bigdecimal("1"));

//GET and SET Methods

I want to avoid doing the cast when calling this method, bearing in mind that it is one of the purposes of the generic, but I have not managed to do it, any ideas? or what I intend to do is not possible.

Upvotes: 0

Views: 126

Answers (2)

Lino
Lino

Reputation: 19926

By introducing a generic type variable on the method level you can define what type should be returned, this can be seen in @cpr4t3s' answer.

You can also shorten his snippet to the following:

public <T> T findByPk(Class<T> clazz, Object pk) throws Exception {
    return entity().find(clazz, pk);
}

Because:

  1. You're just throwing the exception up in the catch-block
  2. You're doing nothing, but return the obj-variable

Upvotes: 1

cpr4t3s
cpr4t3s

Reputation: 1445

You can use generics instead of using Object:

public <T> T findByPk(Class<T> clazz, Object pk) throws Exception {
    T obj = null;
    try {
        obj = entity().find(clazz, pk);
    } catch (Exception e) {
        throw e;
    }
    return obj;
}

And then it should work without doing the cast

private myTypeEntity entity;    
entity = findByPk(myTypeEntity.class, new Bigdecimal("1"));

Upvotes: 2

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