JPA本机查询联接返回对象，但取消引用引发类强制转换异常

Question

我正在使用JPQL本机查询来联接表，查询结果存储在中List<Object[]>。

public String getJoinJpqlNativeQuery() {



            String final SQL_JOIN = 
               "SELECT v1.bitbit, v1.numnum, v1.someTime, t1.username, 
                t1.anotherNum FROM MasatosanTest t1 
                JOIN MasatoView v1 ON v1.username = t1.username;"

            System.out.println("get join jpql native query is being called 
        ============================");

            EntityManager em = null;
            List<Object[]> out = null;
            try {
                em = EmProvider.getDefaultManager();
                Query query = em.createNativeQuery(SQL_JOIN);
                out = query.getResultList();

                System.out.println("return object ==========>" + out);

                System.out.println(out.get(0));

                String one = out.get(0).toString(); //LINE 77 where ClassCastException
                System.out.println(one);
            }
            catch(Exception e) {
            }
            finally {
                if(em != null) { em.close; }
            }
}

问题是

System.out.println("return object ==========>" + out); 输出：

return object ==========>
[[true, 0, 2010-12-21 15:32:53.0, masatosan, 0.020], 
[false, 0, 2010-12-21 15:32:53.0, koga, 0.213]]

System.out.println(out.get(0)) 输出：

[true, 0, 2010-12-21 15:32:53.0, masatosan, 0.020]

所以我假设我可以分配out.get（0）的返回值，该值应该是String：

String one = out.get(0).toString();

但是我得到了奇怪的ClassCastException。

java.lang.ClassCastException: java.util.Vector cannot be cast to 
[Ljava.lang.Object;
        at local.test.jaxrs.MasatosanTestResource.getJoinJpqlNativeQuery
(MasatosanTestResource.java:77)

那么到底是怎么回事？甚至Object[] foo = out.get(0);会抛出ClassCastException :(

Answer 1

我对JPQL本机查询不熟悉，但是您只需使用以下命令进行调试：

对象o = out.get（0）; System.out.println（o.getClass（））;

然后从那里开始。如果是向量，请遍历并查找向量中的内容。