Question

如何在下面实际实例化JPA控制器？

我对如何实际使用Netbeans创建JPA控制器感到困惑。在这种情况下，我当然很欣赏Netbeans向导，这很有趣 - 我试图理解它是如何工作的以及为什么它以这种方式工作。

ejb模块可以从这些行注入Glassfish：

@PersistenceUnit(unitName="JSFPU") //inject from your application server
EntityManagerFactory emf;
@Resource //inject from your application server
UserTransaction utx;

然后，实例化控制器，如下所示：

    PersonEntityJpaController pejc = new PersonEntityJpaController(utx, emf); //create an instance of your jpa controller and pass in the injected emf and utx
    try {
        pejc.create(pe); //persist the entity

在哪里可以找到有关如何注射PU的更多信息，在本例中为Glassfish，以及@Resource的工作原理？我根本不介意从Oracle或其他参考资料中阅读Glassfish for JavaEE文档。

控制器Netbeans生成：

package db;

import db.exceptions.NonexistentEntityException;
import db.exceptions.RollbackFailureException;
import java.io.Serializable;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Query;
import javax.persistence.EntityNotFoundException;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import javax.transaction.UserTransaction;

public class ClientsJpaController implements Serializable {

    public ClientsJpaController(UserTransaction utx, EntityManagerFactory emf) {
        this.utx = utx;
        this.emf = emf;
    }
    private UserTransaction utx = null;
    private EntityManagerFactory emf = null;

    public EntityManager getEntityManager() {
        return emf.createEntityManager();
    }

    public void create(Clients clients) throws RollbackFailureException, Exception {
        EntityManager em = null;
        try {
            utx.begin();
            em = getEntityManager();
            em.persist(clients);
            utx.commit();
        } catch (Exception ex) {
            try {
                utx.rollback();
            } catch (Exception re) {
                throw new RollbackFailureException("An error occurred attempting to roll back the transaction.", re);
            }
            throw ex;
        } finally {
            if (em != null) {
                em.close();
            }
        }
    }

    public void edit(Clients clients) throws NonexistentEntityException, RollbackFailureException, Exception {
        EntityManager em = null;
        try {
            utx.begin();
            em = getEntityManager();
            clients = em.merge(clients);
            utx.commit();
        } catch (Exception ex) {
            try {
                utx.rollback();
            } catch (Exception re) {
                throw new RollbackFailureException("An error occurred attempting to roll back the transaction.", re);
            }
            String msg = ex.getLocalizedMessage();
            if (msg == null || msg.length() == 0) {
                Integer id = clients.getId();
                if (findClients(id) == null) {
                    throw new NonexistentEntityException("The clients with id " + id + " no longer exists.");
                }
            }
            throw ex;
        } finally {
            if (em != null) {
                em.close();
            }
        }
    }

    public void destroy(Integer id) throws NonexistentEntityException, RollbackFailureException, Exception {
        EntityManager em = null;
        try {
            utx.begin();
            em = getEntityManager();
            Clients clients;
            try {
                clients = em.getReference(Clients.class, id);
                clients.getId();
            } catch (EntityNotFoundException enfe) {
                throw new NonexistentEntityException("The clients with id " + id + " no longer exists.", enfe);
            }
            em.remove(clients);
            utx.commit();
        } catch (Exception ex) {
            try {
                utx.rollback();
            } catch (Exception re) {
                throw new RollbackFailureException("An error occurred attempting to roll back the transaction.", re);
            }
            throw ex;
        } finally {
            if (em != null) {
                em.close();
            }
        }
    }

    public List<Clients> findClientsEntities() {
        return findClientsEntities(true, -1, -1);
    }

    public List<Clients> findClientsEntities(int maxResults, int firstResult) {
        return findClientsEntities(false, maxResults, firstResult);
    }

    private List<Clients> findClientsEntities(boolean all, int maxResults, int firstResult) {
        EntityManager em = getEntityManager();
        try {
            CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
            cq.select(cq.from(Clients.class));
            Query q = em.createQuery(cq);
            if (!all) {
                q.setMaxResults(maxResults);
                q.setFirstResult(firstResult);
            }
            return q.getResultList();
        } finally {
            em.close();
        }
    }

    public Clients findClients(Integer id) {
        EntityManager em = getEntityManager();
        try {
            return em.find(Clients.class, id);
        } finally {
            em.close();
        }
    }

    public int getClientsCount() {
        EntityManager em = getEntityManager();
        try {
            CriteriaQuery cq = em.getCriteriaBuilder().createQuery();
            Root<Clients> rt = cq.from(Clients.class);
            cq.select(em.getCriteriaBuilder().count(rt));
            Query q = em.createQuery(cq);
            return ((Long) q.getSingleResult()).intValue();
        } finally {
            em.close();
        }
    }

}

将在控制器上创建和调用方法的类;它旨在为Web模块提供单个队列，以便从以下位置弹出元素（在此int中）：

package db;

import javax.ejb.Singleton;

@Singleton
public class MySingletonQueue implements RemoteQueue {

    private int next = 3;   //dummy
    private ClientsJpaController cjc;  //instantiate how?

    @Override
    public int getNext() {
        return next;  //get next int from perhaps another class or method...
    }

}

for context，网页用EL实例化的bean：

package dur;

import db.RemoteQueue;
import java.io.Serializable;
import java.util.logging.Logger;
import javax.ejb.EJB;
import javax.enterprise.context.SessionScoped;
import javax.inject.Named;

@Named
@SessionScoped
public class MySessionBean implements Serializable {

    @EJB
    private RemoteQueue mySingletonQueue;

    private static final long serialVersionUID = 1L;
    private static final Logger log = Logger.getLogger(MySessionBean.class.getName());

    public MySessionBean() {
    }

    public int getNext() {
        log.info("getting next int from remote EJB");
        return mySingletonQueue.getNext();
    }

}

http://forums.netbeans.org/viewtopic.php?t=47442&highlight=jpa+controller+constructor

Answer 1

答案很简单：

package db;

import javax.ejb.Singleton;


import javax.annotation.PostConstruct;
import javax.ejb.Singleton;

@Singleton
public class MySingletonQueue implements RemoteQueue {

    private int next = 3;
    private ClientsJpaController cjc;

    @PersistenceUnit
    private EntityManagerFactory emf;

    @Resource
    private UserTransaction utx; 

    @PostConstruct
    public void initBean() {
        // Instantiate your controller here
        cjc = new ClientsJpaController(utx, emf);
    }

    // rest of the class ...

}

但请记住，虽然它会起作用，但你所做的事情非常混乱且难以维护，被视为不良做法。

更新

一些建议：

您应该向ClientsJpaController注入实体经理（也考虑将其重命名为ClientDAO）
不管理服务器环境中的事务，让服务器执行此操作。您的代码将简化为几行。
您的实体Clients是复数形式，它应该是单数的，因为它代表单个客户，不是吗？
您绝对不应该执行以下操作：catch (Exception ex) {，因为它是所有异常的根。只捕获最具体的例外。

因此，例如，您的编辑功能可以缩短为：

  public Client edit(Client client) {
    return em.merge(client);
  }

你一定要看一些EJB / JPA书或阅读一些体面的指南。

通过从glassfish注入来实例化JPA控制器

1 个答案:

更新