测试DAO时出错：sun.reflect.generics.reflectiveObjects.TypeVariableImpl无法强制转换为java.lang.Class

Question

I am very new to Spring + Hibernate, and I am running tests to see if my DAOs are working. I get the following error which upon searching in Google yields a lot of different answers (mostly of typos, which I have checked). I'm hoping you can help me out on this:

java.lang.IllegalStateException: Failed to load ApplicationContext
        at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:308)
        at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.injectDependencies(DependencyInjectionTestExecutionListener.java:109)
        at org.springframework.test.context.support.DependencyInjectionTestExecutionListener.prepareTestInstance(DependencyInjectionTestExecutionListener.java:75)
        at org.springframework.test.context.TestContextManager.prepareTestInstance(TestContextManager.java:321)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.createTest(SpringJUnit4ClassRunner.java:220)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner$1.runReflectiveCall(SpringJUnit4ClassRunner.java:301)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.methodBlock(SpringJUnit4ClassRunner.java:303)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:240)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
        at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
        at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
        at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
        at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
        at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
        at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:180)
        at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
        at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:71)
        at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:199)
        at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:62)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
    Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'nominationDao' defined in file [C:\IdeaProjects\Projects\branch\dev\test-dataacess\target\classes\com\dev\test\data\dao\hibernate\NominationHibernateDAO.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.dev.test.data.dao.hibernate.NominationHibernateDAO]: Constructor threw exception; nested exception is java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
        at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:288)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1003)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:907)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:485)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:580)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:900)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:455)
        at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:84)
        at org.springframework.test.context.support.AbstractGenericContextLoader.loadContext(AbstractGenericContextLoader.java:1)
        at org.springframework.test.context.TestContext.loadApplicationContext(TestContext.java:280)
        at org.springframework.test.context.TestContext.getApplicationContext(TestContext.java:304)
        ... 27 more
    Caused by: org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.dev.test.data.dao.hibernate.NominationHibernateDAO]: Constructor threw exception; nested exception is java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:162)
        at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:108)
        at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:280)
        ... 42 more
    Caused by: java.lang.ClassCastException: sun.reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class
        at com.dev.test.data.dao.hibernate.AbstractHibernateDAO.<init>(AbstractHibernateDAO.java:50)
        at com.dev.test.data.dao.hibernate.NominationHibernateDAO.<init>(NominationHibernateDAO.java:36)
        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:147)
        ... 44 more

What could cause this? Please let me know if I have edit in my AbstractHibernateDAO and NominationHibernateDAO.

Thank you!

Edit here are the snippets:

This is a snippet for AbstractHibernateDAO, line 50 is by a comment:

public abstract class AbstractHibernateDAO<T, K extends Serializable>
        implements DAO<T, K> {

    protected Logger logger = LoggerFactory.getLogger(this.getClass());

    private SessionFactory sessionFactory;

    private Class<T> persistentClass;

    protected AbstractHibernateDAO(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
        this.persistentClass = (Class<T>) ((ParameterizedType) //LINE 50
                getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }

Line 36 is followed by a comment on this snippet for NominationHibernateDAO:

@Repository("nominationDao")
public class NominationHibernateDAO<T extends Nomination>
        extends AbstractHibernateDAO<T,Integer>
        implements NominationDAO<T> {


      @Autowired(required = true)
      public NominationHibernateDAO(SessionFactory sessionFactory) {
           super(sessionFactory); //LINE 36
      }

Answer 1

The expression

getClass().getGenericSuperclass()).getActualTypeArguments()[0]

refers to value substituted to first type parameter of AbstractHibernateDAO (which in the AbstractHibernateDAO.java is denoted by T ). The type substituted by subclass NominationHibernateDAO is still not concrete, it is T extends Nomination , which is definitely not a java.lang.Class instance, but a Type instance ( TypeVariableImpl is an implementation of a Type ).

If the NominationHibernateDAO was declared with something like that:

class NominationHibernateDAO extends AbstractHibernateDAO<Nomination, Integer> { ...

then the AbstractHibernateDAO constructor magic would work. Alternatively, you can (or you even should?) instantiate a subclass of NominationHibernateDAO declared like this:

class ConcreteNominationHibernateDAO
        extends NominationHibernateDAO<ConcreteNominationSubclass> { ...

or

new NominationHibernateDAO<ConcreteNominationSubclass>() {}

This, again, would not trigger the problem.

Are you sure the NominationHibernateDAO class is meant to be used as a Spring bean?