无法将java.lang.Class强制转换为java.lang.reflect.ParameterizedType
问题内容：
我长期困扰这个问题。我有一段时间搜索此问题，但没有解决方案。
结构体：
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
我也用<context:component-scan>我application-config.xml + <tx:annotation- driven />在我的application-config.xml。
请提供有关如何解决此问题的一些信息。
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
问题答案：
@Repository从中删除注释AbstractGenericDAO并使其abstract：
public abstract class AbstractGenericDAO<T extends Serializable, ID extends Serializable>
implements GenericDAO<T, ID>
发生您的问题是因为@Repository的特化@Component，这意味着Spring将尝试创建AbstractGenericDAO注入实例。由于AbstractGenericDAOsuperclass（Object）不是通用的，因此您无法将其向下转换Type为ParameterizedType，因此这行代码将失败（与尝试使用手动实例化该代码的方式相同new AbstractGenericDAO()）：
this.persistentClass = (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
专业课ShlkActiveWorkflowDAOImpl仍应使用注释@Repository。当spring尝试创建此类的实例时，AbstractGenericDAO将对构造函数进行隐式调用，但是这一次上面提到的代码行将按预期运行。发生这种情况是因为getClass()return
ShlkActiveWorkflowDAOImpl.class是泛型的子类AbstractGenericDAO（因此向下转换ParameterizedType有效）。
由于ShlkActiveWorkflowDAOImpl extends
AbstractGenericDAO<ShlkActiveWorkflow, Serializable>实际类型ShlkActiveWorkflow将在运行时正确反映。这是避免将Class<T>引用传递给AbstractGenericDAO构造函数的已知解决方法。
如果您对的@Autowired注释感到担心AbstractGenericDAO，请不必担心。当您注入其子类之一的实例时，Spring会正确地连接一切。
