java - JPA 和 Spring 对带有异常和泛型的 DAO 的处理

Question

javax.transaction.TransactionRequiredException' 永远不会在相应的 try block 中抛出

引用:http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html#merge%28T%29

注意:我不想在我的方法签名中声明抛出新异常

如何处理异常？

我认为 .save .merge 可以在所有 DAO 中使用。因此，使用不同的对象(但相同的模式)为每个 DAO 编写相同的代码并不是明智的OOP。

如何正确制作通用.merge .save或所有此类重复的事情。

我在谷歌上找不到太多稳定的例子。

有示例代码吗？

private EntityManager entityManager;

    public Boards save(Boards board) {
          Boards boardToBeReturned = null;
          try{
              boardToBeReturned = entityManager.merge(board);
          }catch (IllegalArgumentException e){
              e.printStackTrace();
          }catch (TransactionRequiredException e){
              e.printStackTrace();
          }

          return boardToBeReturned;
    } 

类的完整示例代码:

package web.dao.impl.jpa;

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.PersistenceContextType;
import javax.transaction.TransactionRequiredException;

import org.hibernate.Session;
import org.springframework.stereotype.Repository;
import web.dao.BoardsDAO;
import web.entity.Boards;
import web.entity.Users;


@Repository
public class BoardsDAOImpl implements BoardsDAO {

    /**
     * The JPA entity manager
     */
//  @Autowired
    @PersistenceContext(type = PersistenceContextType.EXTENDED)
    private EntityManager entityManager;

    public Boards save(Boards board) {
        Boards boardToBeReturned = null;
        try{
            boardToBeReturned = entityManager.merge(board);
        }catch (IllegalArgumentException e){
             e.printStackTrace();
//        }catch (TransactionRequiredException e){
//            e.printStackTrace();
        }
        return boardToBeReturned;
    }


    public Boards getBoardById(Long id){
        Boards boardToBeReturned = null;
        System.out.println("board id entered for lookup was : "+id);
        try {
            boardToBeReturned=entityManager.find(Boards.class, id);
        }catch (IllegalArgumentException e){
               e.printStackTrace();
        }
        return boardToBeReturned;
    }


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

    /**
     * Helper method to return the hibernate session from the JPA
     * entity manager implementation.
     * 
     * @return the hibernate {#link Session}
     */
    protected Session getHibernateSession() {
        return entityManager.unwrap(Session.class);
    }


        public List<Boards> getBoardListByUser(Users user){

            return null;
        }


}

Answer 1

IllegalArgumentException 和 TransactionRequiredException 是运行时异常，表示存在编程错误。你不应该捕获他们。如果你捕获了他们，最糟糕的事情就是像你现在一样忽视他们，假装什么都没发生。您的方法应该如下所示:

public Boards save(Boards board) {
    return entityManager.merge(board);
}

既然您正在使用 Spring 并寻找通用 DAO，那么请查看 Spring Data JPA项目，它提供了这些，以及更多。