hibernate架構之session中get與load方法的區別
hibernate是一個用於連接數據庫的升級版JDBC，與一般JDBC不同的是，hibernate架構是通過hql進行查找，通過session建立連接。其工作原理是：將實例分為瞬時狀態、持久狀態、遊離狀態，通過hql對持久狀態的實例進行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()方法獲取對象時，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，代碼示例如下：
get()方法源代碼：
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()方法源代碼：
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()方法默認使用了懶加載，也就是說調用load()會把數據加載到緩存中，而只有當實際調用時才會在數據庫中執行查找語句，這樣就引起了矛盾：load()得到的實例是持久狀態的實例，實際調用時已經關閉了session，那麽此時的實例就是遊離狀態的實例，只有持久狀態的實例才能在數據庫中得到數據，因此會拋出異常。
hibernate架構之session中get與load方法的區別