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

DAO层有很多操作其实可以用范式加反射来实现的，所以我就开始构想我的万金油BaseDAO了。

BaseHibernateDaoAdvance.java

public class BaseHibernateDaoAdvance<T extends ModifyInfoEntity, PK extends Serializable, DTO extends BaseDto>
        extends HibernateDaoSupport implements BaseDaoAdvance<T, PK, DTO> {

    private final Logger logger = LoggerFactory.getLogger(getClass());

    @Autowired
    private void getSessionFactory(SessionFactory sessionFactory){
        super.setSessionFactory(sessionFactory);
    }

    // 实体类类型(由构造方法自动赋值)
    private Class<T> entityClass;
    private Class<DTO> dtoClass;
    // 构造方法，根据实例类自动获取实体类类型
    public BaseHibernateDaoAdvance() {
        System.out.println("-------------->in BaseHibernateDaoAdvance");

        this.entityClass = null;
        Class c = getClass();
        System.out.println(c);
        Type t = c.getGenericSuperclass();
        System.out.println(t);
        if (t instanceof ParameterizedType) {
            System.out.println("in if");
            Type[] p = ((ParameterizedType) t).getActualTypeArguments();
            System.out.println(Arrays.toString(p));
            this.entityClass = (Class<T>) p[0];
            this.dtoClass = (Class<DTO>) p[2];
        }
    }
}

写好，准备些测试类

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = { "classpath:/config/applicationContext.xml",
"classpath:/config/service.xml","classpath:/config/dao.xml" })
public class BaseDAOImplAdvanceTest {

    private BaseDaoAdvance<Course, Serializable, CourseDTO> baseDAOImpl;

    public BaseDaoAdvance<Course, Serializable, CourseDTO> getBaseDAOImpl() {
        return baseDAOImpl;
    }

    @Autowired
    public void setBaseDAOImpl(
            BaseDaoAdvance<Course, Serializable, CourseDTO> baseDAOImpl) {
        this.baseDAOImpl = baseDAOImpl;
    }

    @Test
    public void queryList(){
        CourseDTO dto = new CourseDTO();
        baseDAOImpl.queryList(dto);
        System.out.println("here-------------------->");
    }
}

但是提示错误java.lang.NullPointerException

了解一下代码，发现应该是这一段判断不通过

        if (t instanceof ParameterizedType) {
            System.out.println("in if");
            Type[] p = ((ParameterizedType) t).getActualTypeArguments();
            System.out.println(Arrays.toString(p));
            this.entityClass = (Class<T>) p[0];
            this.dtoClass = (Class<DTO>) p[2];
        }

去掉if测试一下，还是报错，java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType

~~~~(>_<)~~~~

其实原因是因为范式的使用方式不对。

增加了具体的DAO和实现

public interface CourseDao extends BaseDaoAdvance<Course, Serializable,CourseDTO> {

}

@Repository
public class CourseDaoImpl extends BaseHibernateDaoAdvance<Course, Serializable,CourseDTO> implements CourseDao {

}

测试类

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = { "classpath:/config/applicationContext.xml",
"classpath:/config/service.xml","classpath:/config/dao.xml" })
public class CourseDaoImplTest {
//    private BaseDaoAdvance<Course, Serializable, CourseDTO> baseDAOImpl;
    @Autowired
    private CourseDao courseDao;

    @Test
    public void queryList(){

        CourseDTO dto = new CourseDTO();
        courseDao.queryList(dto);
        System.out.println("here-------------------->");
    }
}

OK，成功！

范式应该在编译的时候就指定，而不是运行时。