spring - java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType

Question

I am stuck with this issue for a long time. I searched for this issue for sometime but none of solution worked.

Structure:

public interface GenericDAO<T extends Serializable, ID extends Serializable>

@Repository
public class AbstractGenericDAO<T extends Serializable, ID extends Serializable> 
    implements GenericDAO<T, ID> {

   private Class<T> persistentClass;

   @Autowired
   private SessionFactory sessionFactory;

   static Logger LOGGER = Logger.getLogger(AbstractGenericDAO.class);


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

   /**
    * @param entity
    * @return T
    * @throws DBException
    */
   @SuppressWarnings("unchecked")
   public T saveEntity(T entity) throws DBException {
       return saveEntity(entity, false);
   }

   /**
    * @param entity
    * @param explicitFlush
    * @return T
    * @throws DBException
    */
   @SuppressWarnings("unchecked")
   public T saveEntity(T entity, boolean explicitFlush) throws DBException {
       Session session = getSessionFactory().getCurrentSession();

       try {
           session.save(entity);
           if(explicitFlush) {
               session.flush();
               session.refresh(entity);
           }
       } catch (HibernateException he) {
           String errorMsg = "Could not save entity. Reason: " + he.getMessage();
           LOGGER.error(errorMsg, he);
           throw new DBException(errorMsg, he);
       }

       return entity;
   }

   /* (non-Javadoc)
    * @see com.amazon.fc.receive.dbaccess.dao.GenericDAO#getPersistentClass()
    */
   @SuppressWarnings("unchecked")
   public Class<T> getPersistentClass() {
       return persistentClass;
   }

   /**
    * @return the sessionFactory
    */
   public SessionFactory getSessionFactory() {
       return this.sessionFactory;
   }

   /**
    * @param sessionFactory the sessionFactory to set
    */
   @Autowired
   public void setSessionFactory(SessionFactory sessionFactory) {
       this.sessionFactory = sessionFactory;
   }
}

public interface ShlkActiveWorkflowDAO 
    extends GenericDAO<ShlkActiveWorkflow, Serializable> 

@Repository
public class ShlkActiveWorkflowDAOImpl 
    extends AbstractGenericDAO<ShlkActiveWorkflow, Serializable>
    implements ShlkActiveWorkflowDAO

I am also using <context:component-scan> in my application-config.xml + <tx:annotation-driven /> in my application-config.xml.

Please provide some information about how to fix this issue.

Exception:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'abstractGenericDAO' 

Constructor threw exception; nested exception is java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:946)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:890)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:479)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:450)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:290)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:287)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:189)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:557)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:842)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:416)
    at com.coral.spring.Launcher.<init>(Launcher.java:95)
    at com.coral.spring.Launcher.main(Launcher.java:56)
Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.workflow.dao.AbstractGenericDAO]: Constructor threw exception; nested exception is     
java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:141)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:72)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:938)
    ... 12 more
Caused by: java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType
    at com.workflow.dao.AbstractGenericDAO.<init>(AbstractGenericDAO.java:43)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:126)
    ... 14 more

Answer 1

Remove @Repository annotation from AbstractGenericDAO and make it abstract:

public abstract class AbstractGenericDAO<T extends Serializable, ID extends Serializable> 
   implements GenericDAO<T, ID>

Your problem occurs because @Repository is a specialization of @Component, which means that Spring will try to create AbstractGenericDAO instances for injection. Since AbstractGenericDAO superclass (Object) is not generic, you will not be able to downcast its Type to ParameterizedType, and so this line of code will fail (in the same way that it would if you tried to instantiate it manually with new AbstractGenericDAO()):

this.persistentClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];

The specialized class ShlkActiveWorkflowDAOImpl should still be annotated with @Repository. When spring tries to create a instance of this class a implicit call to AbstractGenericDAO constructor will occur, but this time the line of code mentioned above will run as expected. This happens because getClass() returns ShlkActiveWorkflowDAOImpl.class which is a subclass of the generic AbstractGenericDAO (so the downcast to ParameterizedType works).

Since ShlkActiveWorkflowDAOImpl extends AbstractGenericDAO<ShlkActiveWorkflow, Serializable> the actual type ShlkActiveWorkflow will be correctly reflected at runtime. This is a known workaround to avoid passing a Class<T> reference to the AbstractGenericDAO constructor.

If you are worried about the @Autowired annotation at AbstractGenericDAO, don't be. Spring will correctly wire everything up when you inject a instance of one of its subclasses.