Question

我正在尝试使用持久性框架检索表

我编写的代码是webapplication中的简单java类文件

java类中的代码

EntityManager em = null;
    EntityManagerFactory emf = null;

public List fname (String id) {
    String fname = null;
    List persons = null;
    try {
        emf = Persistence.createEntityManagerFactory("WebApplicationSecurityPU");
        em = emf.createEntityManager();
        persons = em.createQuery("select r from Roleuser r").getResultList();
        int i=0;
        for (i=0;i<persons.size(); i++)
            System.out.println("Testing n "+ i +" " + persons.get(i));

    } catch(Exception e) {
        System.out.println("" + e);
    }
    finally {
        if(em != null) {
            em.close();
        }
    }
    return persons;
}

但是在运行这个时我得到IllegalArgumentException

是完整的例外

java.lang.IllegalArgumentException：An 创建时出现异常在EntityManager中查询

我认为实体类没有初始化或者没有与数据库连接这就是IllegalArgumentException

的原因

Answer 1

我可以通过代码中的一些更改来纠正它

@PersistenceUnit
public EntityManagerFactory emf;
EntityManager em;


public List fname (String id) {
    String fname = null;
    List persons = null;
    //private PersistenceManagerFactory persistenceManagerFactory;

    try {
        emf = Persistence.createEntityManagerFactory("WebApplicationSecurityPU");

        em = emf.createEntityManager();
        persons = em.createQuery("select r from Roleuser r").getResultList();

        int i=0;
        for (i=0;i<persons.size(); i++)
            System.out.println("Testing n "+ i +" " + persons.get(i));

    } catch(Exception e) {
        System.out.println("" + e);
    }
    finally {
        if(em != null) {
            em.close();
        }
    }
    return persons;
}

谢谢你 Pradyut

持久性查询中的异常

1 个答案: