標籤:游離 結果 資料庫 rom actor 通過 sys 原理 原始碼
hibernate是一個用於串連資料庫的升級版JDBC,與一般JDBC不同的是,hibernate架構是通過hql進行尋找,通過session建立串連。其工作原理是:將執行個體分為瞬時狀態、持久狀態、游離狀態,通過hql對持久狀態的執行個體進行CRUD。在學習的過程中我們遇到了這樣的一個現象:用Session對象調用get()方法和load()方法擷取對象時,類似的代碼會分為兩種結果,get方法運行成功,load方法會報錯,程式碼範例如下:
get()方法原始碼:
Session session= HibernateSessionFactory.getSession();
SysUserEntity user=(SysUserEntity)session.get(SysUserEntity.class,id);
HibernateSessionFactory.closeSession();
運行結果:代碼運行成功
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Hibernate: select sysuserent0_.userId as userId1_0_0_, sysuserent0_.user as
user2_0_0_, sysuserent0_.loginPassWord as loginPas3_0_0_, sysuserent0_.loginUser as
loginUse4_0_0_ from sys_user sysuserent0_ where sysuserent0_.userId=?
曹操
load()方法原始碼:
Session session= HibernateSessionFactory.getSession();
SysUserEntity user=(SysUserEntity)session.load(SysUserEntity.class,id);
HibernateSessionFactory.closeSession();
運行結果:代碼報錯原因是在關閉了session
log4j:WARN No appenders could be found for logger (org.jboss.logging).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.Exception in thread "main" org.hibernate.LazyInitializationException: could not initialize proxy - no Session
at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:165)
at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:286)
at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:185)
at com.lovo.h.entity.SysUserEntity_$$_jvstb09_0.getLoginUser(SysUserEntity_$$_jvstb09_0.java)
at com.lovo.h.test.T.main(T.java:36)
session中的load()方法預設使用了懶載入,也就是說調用load()會把資料載入到緩衝中,而只有當實際調用時才會在資料庫中執行尋找語句,這樣就引起了矛盾:load()得到的執行個體是持久狀態的執行個體,實際調用時已經關閉了session,那麼此時的執行個體就是游離狀態的執行個體,只有持久狀態的執行個體才能在資料庫中得到資料,因此會拋出異常。
hibernate架構之session中get與load方法的區別