java - 测试 DAO 时出错 : sun. reflect.generics.reflectiveObjects.TypeVariableImpl cannot be cast to java.lang.Class

Question

我是 Spring + Hibernate 的新手，我正在运行测试以查看我的 DAO 是否正常工作。我收到以下错误，在 Google 中搜索时会得到很多不同的答案(主要是拼写错误，我已经检查过了)。我希望你能帮我解决这个问题:

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

什么会导致这种情况？如果我在我的 AbstractHibernateDAO 和 NominationHibernateDAO 中进行了编辑，请告诉我。

谢谢!

编辑这里是片段:

这是 AbstractHibernateDAO 的一个片段，第 50 行是评论:

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];
    }

第 36 行之后是针对 NominationHibernateDAO 的这段代码的注释:

@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

表达式

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

是指代入AbstractHibernateDAO的第一个类型参数的值(在AbstractHibernateDAO.java中用T表示)。子类NominationHibernateDAO替换的类型还是不具体，是T extends Nomination，肯定不是java.lang.Class实例，但是一个 Type 实例(TypeVariableImpl 是一个 Type 的实现)。

如果 NominationHibernateDAO 是这样声明的:

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

那么 AbstractHibernateDAO 构造函数就会起作用。或者，您可以(或者您甚至应该？)实例化 NominationHibernateDAO 的子类，声明如下:

class ConcreteNominationHibernateDAO
        extends NominationHibernateDAO<ConcreteNominationSubclass> { ...

或

new NominationHibernateDAO<ConcreteNominationSubclass>() {}

同样，这不会触发问题。

您确定要将 NominationHibernateDAO 类用作 Spring bean 吗？