Question

我是hibernate的新手。当我试图调用session.get（）方法时，Nullpointer Exception正在发生。我该如何解决呢？

我的pojo课程： -

package test;
import java.util.*;

public class user1 implements java.io.Serializable{

private int id;
private String name;
private String department;
private String password;

public user1() {}

public user1(int id,String name, String department, String password) {
      this.id = id;
      this.name = name;
      this.department = department;
      this.password = password;
}

public int getId() {
    return id;
}

public void setId(int id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getDepartment() {
    return department;
}

public void setDepartment(String department) {
    this.department = department;
}

public String getPassword() {
    return password;
}

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

}

我的user1.hbm.xml文件：

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>
<class name="test.user1" table="users">

<id name="id" column="id" type="int">
</id>
<property name="name" column="name" type="string"/>
<property name="department" column="department" type="string"/>
<property name="password" column="password" type="string"/>

</class>
</hibernate-mapping>

我在updateUser（）函数中调用了session.get（user1.class，id）方法。在运行时抛出Nullpointer异常。

public class user2 {

private static SessionFactory factory;
public static void main(String [] args){

    try{
        factory = new Configuration().configure().buildSessionFactory();

    }
    catch (Throwable ex) { 
        System.err.println("SessionFactory object could not be created"+ex);
        throw new ExceptionInInitializerError(ex); 
    }

    user2 User = new user2();
    //User.addUser(3,"cc","cse","cc");
    //User.showUser();
    User.updateUser(Integer.valueOf(3),"dd","cse","dd");

}

public void addUser(int id,String name,String department,String password){
    Session session = factory.openSession();
    Transaction t = null;
    try{
        t = session.beginTransaction();
        user1 User1 = new user1(id,name,department,password);
        session.save(User1);
        t.commit();
    }
    catch (HibernateException e) {
         if (t!=null) t.rollback();
            e.printStackTrace(); 
    }
    finally {
         session.close(); 
    }
}



public void updateUser(Integer id,String name,String department,String password){
    Session session = factory.openSession();
    Transaction t = null;
    try{
        user1 user = (user1)session.get(user1.class,id);

        user.setName(name);
        user.setDepartment(department);
        user.setPassword(password);
        session.update(user);
        t.commit();
    }
    catch (HibernateException e) {
         if (t!=null) t.rollback();
            e.printStackTrace(); 
    }
    finally {
         session.close(); 
    }

}
}

}

Answer 1

Hibernate要求实体表具有主键。故事结束。

Hibernate without Primary Key

Answer 2

您在NullPointerException方法的第t.commit();行获得了updateUser(...)，因为您的事务变量t已在{{1}行初始化为null }}

因此，只需在Transaction t = null;方法中添加此行即可解决问题：

updaeUser

在Hibernate中调用session.get（）方法时出现Nullpointer异常

2 个答案: