java - 无法将类转换为 java.lang.reflect.ParameterizedType

Question

目前 VariableService 在我的 Controller 中是 @Autowired。

我知道我可以实现类 ParameterizedType 来消除这个错误，但我担心我可能会走错方向。有没有更好的方法来做到这一点，还是我需要硬着头皮实现 ParameterizedType 的方法？

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'contentController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.fettergroup.cmt.service.VariableService com.fettergroup.cmt.web.ContentController.variableService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'variableService' defined in ServletContext resource [/WEB-INF/dispatcher-servlet.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [com.fettergroup.cmt.service.VariableService]: Constructor threw exception; nested exception is java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType

可变服务

public class VariableService extends EntityService {
    public VariableService () {
        super.setEntityRepository(new VariableRepository());
    }
}

实体服务

public abstract class EntityService<T> {

    public EntityRepository<T> entityRepository;

    public T create(T entity) {
        return entityRepository.create(entity);
    }

    public T update(T entity) {
        return entityRepository.update(entity);
    }

    public void delete(T entity) {
        entityRepository.delete(entity);
    }

    public void setEntityRepository(EntityRepository<T> entityRepository) {
        this.entityRepository = entityRepository;
    }
}

变量存储库

public class VariableRepository extends EntityRepository {

}

实体库

@Repository
public abstract class EntityRepository<T> {

    //the equivalent of User.class
    protected Class<T> entityClass;

    @PersistenceContext(type= PersistenceContextType.TRANSACTION)
    public EntityManager entityManager;

    public EntityRepository () {
        //Get "T" and assign it to this.entityClass
        ParameterizedType genericSuperclass = (ParameterizedType) getClass().getGenericSuperclass();
        this.entityClass = (Class<T>) genericSuperclass.getActualTypeArguments()[0];
    }

    /**
     * Create this entity
     * @param t
     * @return 
     */
    public T create(T t) {
        entityManager.persist(t);
        return t;
    }

    /**
     * Update this entity
     * @param t
     * @return 
     */
    public T update(T t) {
        return entityManager.merge(t);
    }

    /**
     * Delete this entity
     * @param entity 
     */
    public void delete(T t) {
        t = this.update(t);
        entityManager.remove(t);
    }

    public void setEntityManager(EntityManager entityManager) {
        this.entityManager = entityManager;
    }
}

Answer 1

只是说，这是一个非常糟糕的确定实体类型的设计。您应该执行以下操作，而不是依靠反射来推断其类定义。它不仅会消除该错误，而且总体上会更干净，在低级别上比反射更快(并不是说它真的会成为问题)。

@Repository
public abstract class EntityRepository<T>{
    protected Class<T> entityClass;

    public EntityRepository(Class<T> entityClass){
        this.entityClass = entityClass;
    }

    //...
}


public class UserEntityRepository extends EntityRepository<User>{
    public UserEntityRepository(){
        super(User.class);
    }
}