摘要:引言再回顾一下问题场景教师班级学生在单元测试中跑这段代码,是报错的,,说明执行完之后,就已经关闭了。如果是在单元测试中,就去想想是不是事务配错了,导致挂掉了。兹可谓一劳而久逸。班固封燕然山铭一劳永逸,这是程序员最快乐的时候。
引言
再回顾一下问题场景:
Iterableteachers = teacherRepository.findAll(); for (Teacher teacher : teachers) { logger.debug("教师: " + teacher.getName()); for (Klass klass : teacher.getKlasses()) { logger.debug("班级: " + klass.getName()); for (Student student : klass.getStudents()) { logger.debug("学生: " + student.getName()); } } }
在单元测试中跑这段代码,是报错的,no Session,说明执行完teacherRepository.findAll()之后,session就已经关闭了。继续执行,session已经关闭,再去数据库查教师关联的班级信息,就错了。
然而呢?把这段代码再放到Service里,写一个接口,交给浏览器去调用,却正常执行,说明session还在。
然后就一直研究为什么不好使?如果能把这个原因分析明白,以后再遇到no session错误的时候就可以一劳永逸了。
探究 调试调试最简单的方法就是中断,但是咱水平还不行,也不知道JPA内部去找Hibernate怎么调用的,中断哪个方法呢?
后台发现了另一种调试的方法,JPA的源码中也是像我们开发时经常写日志的,logger.debug()什么的。
slf4j中常用的日志级别就ERROR、WARN、INFO、DEBUG四种,我们可以将JPA的日志级别设置为DEBUG级别,这样我们就可以根据日志推测到JPA内部到底是怎么执行的了。
修改日志级别logging.level.org.springframework.orm.jpa=debug
修改配置文件,将JPA的日志级别设置为DEBUG。
在单元测试中执行完整日志:
2019-06-06 11:36:40.415 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly 2019-06-06 11:36:40.416 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Opened new EntityManager [SessionImpl(1334204880分析)] for JPA transaction 2019-06-06 11:36:40.429 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@73b74615] 2019-06-06 11:36:40.449 INFO 11391 --- [ main] o.h.h.i.QueryTranslatorFactoryInitiator : HHH000397: Using ASTQueryTranslatorFactory Hibernate: select teacher0_.id as id1_2_, teacher0_.name as name2_2_ from teacher teacher0_ 2019-06-06 11:36:40.598 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Initiating transaction commit 2019-06-06 11:36:40.598 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Committing JPA transaction on EntityManager [SessionImpl(1334204880 )] 2019-06-06 11:36:40.601 DEBUG 11391 --- [ main] o.s.orm.jpa.JpaTransactionManager : Closing JPA EntityManager [SessionImpl(1334204880 )] after transaction 2019-06-06 11:36:40.602 DEBUG 11391 --- [ main] com.yunzhiclub.jpa.JpaApplicationTests : 教师: 张三 org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.yunzhiclub.jpa.entity.Teacher.klasses, could not initialize proxy - no Session
Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly Opened new EntityManager [SessionImpl(1334204880)] for JPA transaction Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@73b74615] HHH000397: Using ASTQueryTranslatorFactory Hibernate: select teacher0_.id as id1_2_, teacher0_.name as name2_2_ from teacher teacher0_ Initiating transaction commit Committing JPA transaction on EntityManager [SessionImpl(1334204880 )]
上来是先执行了一个事务,为什么会有事务呢?
JPA创建的仓库实现是SimpleJpaRepository,我们看看源码:
实现类上添加了事务注解,并采用了默认的REQUIRED传播级别。
如果当前存在事务,则使用当前事务。如果不存在任何事务,则创建一个新的事务。
当前不存在事务,所以是teacherRepository.findAll()方法自己创建的事务。
Hibernate: select teacher0_.id as id1_2_, teacher0_.name as name2_2_ from teacher teacher0_ Initiating transaction commit Committing JPA transaction on EntityManager [SessionImpl(1334204880)] Closing JPA EntityManager [SessionImpl(1334204880 )] after transaction 教师: 张三 org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.yunzhiclub.jpa.entity.Teacher.klasses, could not initialize proxy - no Session
再接着看下面的日志,执行了数据库的查询操作,提交了一个事务,然后Closing JPA EntityManager [SessionImpl(1334204880
事务执行之后,就关闭了EntityManager,也就是Hibernate中的Session。
Session is a hibernate-specific API, EntityManager is a standardized API for JPA.
EntityManager和Session还是有一些差别的,但是我们目前还未接触到底层的实现,只需要把他们当成一个东西,只不过在不同领域叫法不同罢了。
在SpringMVC中执行执行得很顺利,完整日志如下:
2019-06-06 11:58:28.788 DEBUG 11443 --- [nio-8080-exec-1] o.j.s.OpenEntityManagerInViewInterceptor : Opening JPA EntityManager in OpenEntityManagerInViewInterceptor 2019-06-06 11:58:28.800 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Found thread-bound EntityManager [SessionImpl(193939447分析)] for JPA transaction 2019-06-06 11:58:28.800 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly 2019-06-06 11:58:28.808 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@56eb5438] 2019-06-06 11:58:28.820 INFO 11443 --- [nio-8080-exec-1] o.h.h.i.QueryTranslatorFactoryInitiator : HHH000397: Using ASTQueryTranslatorFactory Hibernate: select teacher0_.id as id1_2_, teacher0_.name as name2_2_ from teacher teacher0_ 2019-06-06 11:58:28.897 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Initiating transaction commit 2019-06-06 11:58:28.898 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Committing JPA transaction on EntityManager [SessionImpl(193939447 )] 2019-06-06 11:58:28.901 DEBUG 11443 --- [nio-8080-exec-1] o.s.orm.jpa.JpaTransactionManager : Not closing pre-bound JPA EntityManager after transaction 2019-06-06 11:58:28.902 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 教师: 张三 Hibernate: select klasses0_.teacher_id as teacher_3_0_0_, klasses0_.id as id1_0_0_, klasses0_.id as id1_0_1_, klasses0_.name as name2_0_1_, klasses0_.teacher_id as teacher_3_0_1_ from klass klasses0_ where klasses0_.teacher_id=? 2019-06-06 11:58:28.915 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 班级: 软件工程 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 2019-06-06 11:58:28.917 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: Hello Kitty 2019-06-06 11:58:28.917 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 史努比 2019-06-06 11:58:28.917 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 班级: 网络工程 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 2019-06-06 11:58:28.919 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 米老鼠 2019-06-06 11:58:28.919 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 唐老鸭 2019-06-06 11:58:28.919 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 教师: 李四 Hibernate: select klasses0_.teacher_id as teacher_3_0_0_, klasses0_.id as id1_0_0_, klasses0_.id as id1_0_1_, klasses0_.name as name2_0_1_, klasses0_.teacher_id as teacher_3_0_1_ from klass klasses0_ where klasses0_.teacher_id=? 2019-06-06 11:58:28.921 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 班级: 计算机科学与技术 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 2019-06-06 11:58:28.923 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 哪吒 2019-06-06 11:58:28.923 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 小竹熊 2019-06-06 11:58:28.923 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 班级: 物联网 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 2019-06-06 11:58:28.925 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 喜羊羊 2019-06-06 11:58:28.925 DEBUG 11443 --- [nio-8080-exec-1] c.y.jpa.service.TeacherServiceImpl : 学生: 灰太狼 2019-06-06 11:58:28.944 DEBUG 11443 --- [nio-8080-exec-1] o.j.s.OpenEntityManagerInViewInterceptor : Closing JPA EntityManager in OpenEntityManagerInViewInterceptor
Opening JPA EntityManager in OpenEntityManagerInViewInterceptor Found thread-bound EntityManager [SessionImpl(193939447)] for JPA transaction Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findAll]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@56eb5438] HHH000397: Using ASTQueryTranslatorFactory Hibernate: select teacher0_.id as id1_2_, teacher0_.name as name2_2_ from teacher teacher0_ Initiating transaction commit Committing JPA transaction on EntityManager [SessionImpl(193939447 )]
这段没什么说的,和上面一样,创建事务,执行完提交事务。
Not closing pre-bound JPA EntityManager after transaction 教师: 张三 Hibernate: select klasses0_.teacher_id as teacher_3_0_0_, klasses0_.id as id1_0_0_, klasses0_.id as id1_0_1_, klasses0_.name as name2_0_1_, klasses0_.teacher_id as teacher_3_0_1_ from klass klasses0_ where klasses0_.teacher_id=? 班级: 软件工程 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 学生: Hello Kitty 学生: 史努比 班级: 网络工程 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 学生: 米老鼠 学生: 唐老鸭 教师: 李四 Hibernate: select klasses0_.teacher_id as teacher_3_0_0_, klasses0_.id as id1_0_0_, klasses0_.id as id1_0_1_, klasses0_.name as name2_0_1_, klasses0_.teacher_id as teacher_3_0_1_ from klass klasses0_ where klasses0_.teacher_id=? 班级: 计算机科学与技术 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 学生: 哪吒 学生: 小竹熊 班级: 物联网 Hibernate: select students0_.klass_id as klass_id4_1_0_, students0_.id as id1_1_0_, students0_.id as id1_1_1_, students0_.email as email2_1_1_, students0_.klass_id as klass_id4_1_1_, students0_.name as name3_1_1_ from student students0_ where students0_.klass_id=? 学生: 喜羊羊 学生: 灰太狼 Closing JPA EntityManager in OpenEntityManagerInViewInterceptor
这块就有意思了。
第一行:Not closing pre-bound JPA EntityManager after transaction
最后一行:Closing JPA EntityManager in OpenEntityManagerInViewInterceptor
在事务之后没有关闭Session,一直到最后,才将Session关闭,所以没出错。
而在单元测试中呢?Closing JPA EntityManager [SessionImpl(1334204880
找着关键了,Service里好使是因为Session在findAll的事务执行完之后没有关闭。
之前怎么没发现呢?StackOverflow上这老哥和我是一样的问题:Hibernate jpa entity manager not being closed in spring service layer - StackOverflow
User和Address一对多。
我写了一个getUser方法,惰性加载的一对多,但是为什么序列化的时候去找addresses的时候,它不报lazy initialization的错误呢?
这是回答,大家注意一下我圈起来的几个关键词:
OpenEntityManagerInViewInterceptor:在Spring Boot项目中,Session是归OpenEntityManagerInViewInterceptor管理的,这个是干什么的呢?
它是确保EntityManager(Session)一直保持开启的状态,直到请求结束之后(complete request)。所以session在本次请求中,一直open着,惰性加载的数据随便查。
如果你不想这么干,你可以配置spring.jpa.open-in-view=false来禁用此行为。
作将spring.jpa.open-in-view配置为false作一把。
果然,session关闭了,报错位置在TeacherServiceImpl第28行,就是查询惰性加载的klasses出错了。
总结从上周想到这个问题开始,到今天解决,也是花了许久的时间。
所以以后再遇到no session的问题,如果是在项目里的,就先去想想是不是complete request了,请求结束前,session一直有效。
如果是在单元测试中,就去想想是不是事务配错了,导致session挂掉了。
兹可谓一劳而久逸。暂费而永无宁者也。 ——班固《封燕然山铭》
一劳永逸,这是程序员最快乐的时候。
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