Spring Generic Dao class name

Question

I have configured a custom generic service DAO for my spring / hibernate project - the idea being that I can reuse it easily from my controllers.

It essentially looks like this:

public class DefaultService<T> {

private Class<T> e;

public String className(Class<T> e) {
    String clip = e.getName();
    clip = clip.substring(clip.lastIndexOf('.') + 1, clip.length());
    return clip;
}
public List<T> getAll(Integer status) {
    Session session = sessionFactory.getCurrentSession();
    Query query = session.createQuery("FROM " + className(e) + " WHERE status = " + status);
    return query.list();
}
...

Which gets referenced by:

@Autowired
public DefaultService<Address> addressService;
addressService.get(1);

However the String clip = e.getName() line throws a Null pointer exception. I can get this to work if I move the class into the attributes section (so addressService.get(Address.class, 1) but I find this somewhat untidy, especially when there are multiple different classes being called upon.

Is there some way to get the class to generate a value correctly without repeatedly adding it into all my functions?

Thanks in advance.

Answer 1

I did something similar, you need the generic class to be a constructor argument as well, mine uses hibernate entities, but you could pass in the string of table name.

public class DomainRepository<T> {

    @Resource(name = "sessionFactory")
    protected SessionFactory sessionFactory;

 public DomainRepository(Class genericType) {
        this.genericType = genericType;
    }

 @Transactional(readOnly = true)
    public T get(final long id) {
        return (T) sessionFactory.getCurrentSession().get(genericType, id);
    }

You can then subclass (if you need to) to customize or simply set up you bean in the spring config like below t :

<bean id="tagRepository" class="com.yourcompnay.data.DomainRepository">
        <constructor-arg value="com.yourcompnay.domain.Tag"/>
</bean>

So in your code you could then reference tagRepository like so (no other cod eis needed than that posted above, and below) :

@Resource(name = "tagRepository")
private DomainRepository<Tag> tagRepository;

Also, I would call it a repository not a service, a service deals with different types and their interactions (not just one). And for specifically your example using SQL strings :

public final String tableName;
public DomainRepository(String tableName) {
      this.tableName = tableName;
}
public List<T> getAll(Integer status) {
    Session session = sessionFactory.getCurrentSession();
    Query query = session.createQuery("FROM " + tableName + " WHERE status = " + status);
    return query.list();
}

and have your beans defined like so

<bean id="addressRepository" class="com.yourcompnay.data.DomainRepository">
  <constructor-arg value="address"/>
</bean>

And then you can alsow create subclasses youself where necessary :

public class PersonRepository extends DomainRepository<Person> {
    public PersonRepository(){
        super("person"); //assumes table name is person
    }