null在entityManager中的nullpointerexception

我正在使用Hibernate註釋項目，我有問題instanciating EntityManager ..當嘗試EntityManager.find（）我得到一個nullpointerexception 我不明白爲什麼！請幫忙嗎？這裏是一些代碼null在entityManager中的nullpointerexception

Users.java 
    package com.rimweb.users.persistance; 

    // Generated 6 mars 2014 12:00:34 by Hibernate Tools 3.4.0.CR1 

    import javax.persistence.Column; 
    import javax.persistence.Entity; 
    import javax.persistence.FetchType; 
    import javax.persistence.GeneratedValue; 
    import javax.persistence.GenerationType; 

    import static javax.persistence.GenerationType.IDENTITY; 
    import javax.persistence.Id; 
    import javax.persistence.JoinColumn; 
    import javax.persistence.ManyToOne; 
    import javax.persistence.Table; 

    /** 
    * Users generated by hbm2java 
    */ 
    @Entity 
    @Table(name = "users", catalog = "user") 
    public class Users implements java.io.Serializable { 

private Integer userid; 
private Address address; 
private String username; 
private String password; 
private String firstname; 
private String lastname; 
private String email; 

public Users() { 
} 

public Users(Address address, String username, String password, 
     String firstname, String lastname, String email) { 
    this.address = address; 
    this.username = username; 
    this.password = password; 
    this.firstname = firstname; 
    this.lastname = lastname; 
    this.email = email; 
} 

@Id 
@GeneratedValue(strategy =GenerationType.IDENTITY) 
@Column(name = "userid", unique = true, nullable = false) 
public Integer getUserid() { 
    return this.userid; 
} 

public void setUserid(Integer userid) { 
    this.userid = userid; 
} 

@ManyToOne(fetch = FetchType.LAZY) 
@JoinColumn(name = "addressid") 
public Address getAddress() { 
    return this.address; 
} 

public void setAddress(Address address) { 
    this.address = address; 
} 

@Column(name = "username") 
public String getUsername() { 
    return this.username; 
} 

public void setUsername(String username) { 
    this.username = username; 
} 

@Column(name = "password", length = 64) 
public String getPassword() { 
    return this.password; 
} 

public void setPassword(String password) { 
    this.password = password; 
} 

@Column(name = "firstname") 
public String getFirstname() { 
    return this.firstname; 
} 

public void setFirstname(String firstname) { 
    this.firstname = firstname; 
} 

@Column(name = "lastname") 
public String getLastname() { 
    return this.lastname; 
} 

public void setLastname(String lastname) { 
    this.lastname = lastname; 
} 

@Column(name = "email") 
public String getEmail() { 
    return this.email; 
} 

public void setEmail(String email) { 
    this.email = email; 
} 

@Override 
public String toString() { 
    return "Users [userid=" + userid + ", username=" + username 
      + ", password=" + password + ", firstname=" + firstname 
      + ", lastname=" + lastname + ", email=" + email + "]"; 
} 

/* (non-Javadoc) 
* @see java.lang.Object#hashCode() 
*/ 
@Override 
public int hashCode() { 
    final int prime = 31; 
    int result = 1; 
    result = prime * result + ((address == null) ? 0 : address.hashCode()); 
    result = prime * result + ((email == null) ? 0 : email.hashCode()); 
    result = prime * result 
      + ((firstname == null) ? 0 : firstname.hashCode()); 
    result = prime * result 
      + ((lastname == null) ? 0 : lastname.hashCode()); 
    result = prime * result 
      + ((password == null) ? 0 : password.hashCode()); 
    result = prime * result + ((userid == null) ? 0 : userid.hashCode()); 
    result = prime * result 
      + ((username == null) ? 0 : username.hashCode()); 
    return result; 
} 

/* (non-Javadoc) 
* @see java.lang.Object#equals(java.lang.Object) 
*/ 
@Override 
public boolean equals(Object obj) { 
    if (this == obj) 
     return true; 
    if (obj == null) 
     return false; 
    if (getClass() != obj.getClass()) 
     return false; 
    Users other = (Users) obj; 
    if (address == null) { 
     if (other.address != null) 
      return false; 
    } else if (!address.equals(other.address)) 
     return false; 
    if (email == null) { 
     if (other.email != null) 
      return false; 
    } else if (!email.equals(other.email)) 
     return false; 
    if (firstname == null) { 
     if (other.firstname != null) 
      return false; 
    } else if (!firstname.equals(other.firstname)) 
     return false; 
    if (lastname == null) { 
     if (other.lastname != null) 
      return false; 
    } else if (!lastname.equals(other.lastname)) 
     return false; 
    if (password == null) { 
     if (other.password != null) 
      return false; 
    } else if (!password.equals(other.password)) 
     return false; 
    if (userid == null) { 
     if (other.userid != null) 
      return false; 
    } else if (!userid.equals(other.userid)) 
     return false; 
    if (username == null) { 
     if (other.username != null) 
      return false; 
    } else if (!username.equals(other.username)) 
     return false; 
    return true; 
} 



} 

    UsersHome.java: 

    package com.rimweb.users.dao; 

    // Generated 6 mars 2014 16:42:25 by Hibernate Tools 3.4.0.CR1 

    import java.util.ArrayList; 
    import java.util.List; 

    import javax.ejb.Stateless; 
    import javax.persistence.EntityManager; 
    import javax.persistence.EntityManagerFactory; 
    import javax.persistence.Persistence; 
    import javax.persistence.PersistenceContext; 
    import javax.persistence.PersistenceUnit; 
    import javax.persistence.Query; 

    import org.apache.commons.logging.Log; 
    import org.apache.commons.logging.LogFactory; 

    import com.rimweb.users.persistance.Users; 

    /** 
    * Home object for domain model class Users. 
    * @see com.rimweb.users.dao.Users 
    * @author Hibernate Tools 
    */ 
    @Stateless 
    public class UsersHome { 

private static final Log log = LogFactory.getLog(UsersHome.class); 

@PersistenceContext(unitName="manager1") 
//@PersistenceUnit 
//EntityManagerFactory entityManagerFactory=  Persistence.createEntityManagerFactory("manager1"); 
//private EntityManager entityManager = entityManagerFactory.createEntityManager(); 
private EntityManager entityManager; 

public void persist(Users transientInstance) { 
    log.debug("persisting Users instance"); 
    try { 
     entityManager.persist(transientInstance); 
     log.debug("persist successful"); 
    } catch (RuntimeException re) { 
     log.error("persist failed", re); 
     throw re; 
    } 
} 

public void remove(Users persistentInstance) { 
    log.debug("removing Users instance"); 
    try { 
     entityManager.remove(persistentInstance); 
     log.debug("remove successful"); 
    } catch (RuntimeException re) { 
     log.error("remove failed", re); 
     throw re; 
    } 
} 

public Users merge(Users detachedInstance) { 
    log.debug("merging Users instance"); 
    try { 
     Users result = entityManager.merge(detachedInstance); 
     log.debug("merge successful"); 
     return result; 
    } catch (RuntimeException re) { 
     log.error("merge failed", re); 
     throw re; 
    } 
} 

public Users findById(Integer id) { 
    log.debug("getting Users instance with id: " + id); 
    try { 
     Users instance = entityManager.find(Users.class, id); 
     log.debug("get successful"); 
     return instance; 
    } catch (RuntimeException re) { 
     log.error("get failed", re); 
     throw re; 
    } 
} 

public List<Users> findAll() { 
    log.debug("getting all User instances"); 
    try { 
     Query query = entityManager.createQuery("select u from Users u"); 
     List<Users> usersList = (List<Users>) query.getResultList(); 
     log.debug("findAll successful"); 
     return usersList; 
    } catch (RuntimeException re) { 
     log.error("findAll failed", re); 
     return new ArrayList<Users>(); 
    } 
    } 
    } 


    MainTest.java 

    package com.rimweb.users.dao; 
    import java.math.BigDecimal; 
    import java.util.List; 
    import org.hibernate.Session; 
    import org.hibernate.criterion.Order; 
    import com.rimweb.users.persistance.Users; 

    public class MainTest { 

/** 
* @param args 
*/ 
public static void main(String[] args) { 
    // TODO Auto-generated method stub 
    UsersHome dao = new UsersHome() ; 

    Users us = dao.findById(new Integer(1)); 
    System.out.println("-Livre :"+us); 

    ////////////////////////////////////////// 

    List<Users> list = dao.findAll(); 
    for(Users l : list) 
    { System.out.println("##"+l);} 


    } 

}

來源

2014-03-07 Developer007

的persistence.xml： – Developer007

在你UserHome.java類有實體管理器，但因爲要創建EntityManager的只是你已經將它定義爲null。

所以當創建實體管理器，請創建的Util類...

例如HibernateUtil.java

public class HibernateUtil { 

    private static final EntityManagerFactory entityManagerFactory; 
    static { 
       try { 
        entityManagerFactory = Persistence.createEntityManagerFactory("abc"); 

       } catch (Throwable ex) { 

        System.err.println("Initial SessionFactory creation failed." + ex); 
        throw new ExceptionInInitializerError(ex); 

        } 
    } 

public static EntityManagerFactory getEntityManagerFactory() { 
     return entityManagerFactory; 
    } 

}

而下面的方法，而不是ABC提供您的持久性單元名稱。

entityManagerFactory = Persistence.createEntityManagerFactory("abc");

然後在您的每個方法中使用事務創建實體管理器。

例如...

public Users merge(Users detachedInstance) { 
    log.debug("merging Users instance"); 
    try { 
     em = HibernateUtil.getEntityManagerFactory().createEntityManager(); 
    em.getTransaction().begin(); 
     Users result = entityManager.merge(detachedInstance); 
     em.getTransaction().commit(); 
    em.close(); 
     log.debug("merge successful"); 
     return result; 
    } catch (RuntimeException re) { 
     em.getTransaction().rollback(); 
     log.error("merge failed", re); 
     throw re; 
    } 
}

這足以爲避免空指針異常....

來源

2014-03-07 17:14:37

謝謝兄弟..我不知道可能是IA具有在我測試它們之前在JBoss服務器上部署這些實體，因爲我使用的是EJB？ – Developer007

是的，你是對的。 –

null在entityManager中的nullpointerexception

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