关于JPA(Hibernate)+spring在未使用web的情况下使用懒加载,导致no sesssion or session has closed!

来源：互联网发布：公司网络时断时续编辑：程序博客网时间：2024/05/05 19:44

Spring与JPA结合时,如何解决懒加载no session or session was closed!!!

请注意,是懒加载的情况下...

如:

@Entity
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
@ManyToOne(cascade = { CascadeType.PERSIST }, optional = false, fetch = FetchType.LAZY)
private Teacher banzhuren;
@Entity
public class Teacher {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private Integer id;
@OneToMany(cascade = { CascadeType.ALL }, fetch = FetchType.LAZY, mappedBy = "banzhuren")
private Set <Student> students = new HashSet <Student>();

直接使用EntityManager对象的时候并不会出错,如:

@Test
public void testRead(){
Teacher teacher = manager.find(Teacher.class, 1);
System.out.println(teacher.getId());
System.out.println(teacher.getStudents().size());
}
@Test
public void testRead2(){
Student student = manager.find(Student.class, 1);
System.out.println(student.getId());
System.out.println(student.getBanzhuren().getId());
}

但是,在使用Spring后,封装EntityManager后,如:TeacherService中使用EntityManager,单独读取Teacher或Student正常,但是在读取Tacher后,读取Student,就会出现no session or session was closed的懒加载异常...

如果,不设置懒加载,几乎代码是没有什么问题的...为什么设置懒加载后,spring与JPA集合使用就出现这个异常...

这个异常的原因,我的理解是spring上的一个不足...

因为,如果是开发的web项目.这个问题,可以在web.xml中增加配置:

<filter>
        <filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
        <filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
    </filter>
<filter-mapping>
        <filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
        <url-pattern>/*</url-pattern>
</filter-mapping>

当session closed!而需要session的时候,就会自动获取session...从而解决以上的问题....而在不是web项目的开发时候(或者单元测试的时候),这个问题的解决办法,尚未找到...请高人留言...

0 0