Hibernate学习之get和load区别
结论：
insert()：插入记录并将同步更新到session缓存。
update()：更新记录并同步更新到session缓存。
delete()：删除记录并同步更新session缓存。
get()： 如果缓存中存在要查找的记录，直接返回该条记录。
如果缓存中不存在要查找的记录，则执行查询语句，在数据库中查找。
load()：若上次已执行过load，也查找不到该记录并抛出ObjectNotFoundException异常，则这次也会直接抛出异常，不会再执行Sql查询，而且不管在这中间是否插入了记 录。
若上次已执行过get，也查找不到该记录并返回Null，这次依旧会执行SQL查询，若查找不到抛出ObjectNotFoundException异常。
实例：
代码：
@Test
public void test9(){
try{
test1();
Session s = sessionFactory.openSession();
System.out.println(s.get(Person.class, 1L));//get查询
System.out.println(s.get(Person.class, 1L));//get查询
System.out.println(s.load(Person.class, 1L));//load查询
System.out.println(s.load(Person.class, 2L));
System.out.println(s.get(Person.class, 2L));
System.out.println(s.get(Person.class, 3L));
System.out.println(s.get(Person.class, 3L));
try{
System.out.println(s.load(Person.class, 3L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
save(s, 3L);
try{
System.out.println(s.load(Person.class, 3L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
System.out.println(s.get(Person.class, 3L));
System.out.println(s.load(Person.class, 3L));
try{
System.out.println(s.load(Person.class, 4L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
save(s, 4L);
try{
System.out.println(s.load(Person.class, 4L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
Person p = (Person) s.get(Person.class, 4L);
System.out.println(s.get(Person.class, 4L));
System.out.println(s.load(Person.class, 4L));
p.setAge(121212);
update(s, p);
System.out.println(s.get(Person.class, 4L));
delete(s, p);
System.out.println(s.get(Person.class, 4L));
try{
System.out.println(s.load(Person.class, 4L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
}日志：
Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?) Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?) Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? Person [id=1, name=张三, age=12, birthDay=2014-08-29] Person [id=1, name=张三, age=12, birthDay=2014-08-29] Person [id=1, name=张三, age=12, birthDay=2014-08-29] Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? Person [id=2, name=李四, age=22, birthDay=2014-08-29] Person [id=2, name=李四, age=22, birthDay=2014-08-29] Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? null Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? null Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#3] Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?) ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#3] Person [id=3, name=张三, age=12, birthDay=Fri Aug 29 16:33:31 CST 2014] Person [id=3, name=张三, age=12, birthDay=Fri Aug 29 16:33:31 CST 2014] Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4] Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?) ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4] Person [id=4, name=张三, age=12, birthDay=Fri Aug 29 16:33:31 CST 2014] Person [id=4, name=张三, age=12, birthDay=Fri Aug 29 16:33:31 CST 2014] Hibernate: update person set pname=?, birthDay=?, age=? where pid=? Person [id=4, name=张三, age=121212, birthDay=Fri Aug 29 16:33:31 CST 2014] Hibernate: delete from person where pid=? Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? null Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=? ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
日志分析：
@Test
public void test9(){
try{
test1();
//新增id为1，2的两条记录
//Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?)
//Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?)
Session s = sessionFactory.openSession();
System.out.println(s.get(Person.class, 1L));//get查询
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
// Person [id=1, name=张三, age=12, birthDay=2014-08-29]
//分析：执行了查询语句，查到了id为1的记录
System.out.println(s.get(Person.class, 1L));//get查询
//日志输出：Person [id=1, name=张三, age=12, birthDay=2014-08-29]
//分析： 没有执行查询语句，直接获取了结果，说明上次get获取的结果已存入session,而这次get发现session中已存在id为1的记录，直接返回
System.out.println(s.load(Person.class, 1L));//load查询
//日志输出：Person [id=1, name=张三, age=12, birthDay=2014-08-29]
//分析：没有执行查询语句，直接获取了结果，说明上次get获取的结果已存入session,而这次load发现session中已存在id为1的记录，直接返回
System.out.println(s.load(Person.class, 2L));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
// Person [id=2, name=李四, age=22, birthDay=2014-08-29]
//分析：session中没有id为2的记录，执行查询语句，找到了id为2的记录
System.out.println(s.get(Person.class, 2L));
//日志输出：Person [id=2, name=李四, age=22, birthDay=2014-08-29]
//分析：没有执行查询语句，直接获取了结果，说明上次load获取的结果已存入session,而这次get发现session中已存在id为2的记录，直接返回
System.out.println(s.get(Person.class, 3L));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
//null
//分析：查询session缓存中没找到id为3的记录，执行查询语句，也没有查到id为3的记录，返回Null
System.out.println(s.get(Person.class, 3L));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
// null
//分析：在session中没有找到id为3的记录，再次执行查询语句，也没有查到id为3的记录，返回Null
try{
System.out.println(s.load(Person.class, 3L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
// ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
//分析：查询缓冲不存在id为3的记录，执行查询语句，在数据库中也未发现id为3的记录，抛出异常，说明未采用上次get的结果
}
save(s, 3L);
//日志输出：Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?)
//分析：执行插入记录的语句
try{
System.out.println(s.load(Person.class, 3L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
//分析：查询缓冲不存在id为3的记录，但未执行查询语句，抛出异常，说明直接采用了上次load的结果
}
System.out.println(s.get(Person.class, 3L));
//Person [id=3, name=张三, age=12, birthDay=2014-08-29]
//分析：缓冲存在id为3的记录，直接返回。说明save时已经更新了缓存中的记录
System.out.println(s.load(Person.class, 3L));
//日志输出：Person [id=3, name=张三, age=12, birthDay=2014-08-29]
//分析：缓存中存在id为3的记录，直接返回，不执行查询语句
try{
System.out.println(s.load(Person.class, 4L));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
//分析：缓存中不存在id为4的记录，执行查询语句
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
//分析：在数据库中也未查到相应的记录，抛出异常
}
save(s, 4L);
//日志输出：Hibernate: insert into person (pname, birthDay, age, pid) values (?, ?, ?, ?)
//分析：保存id为4的记录
try{
System.out.println(s.load(Person.class, 4L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
//分析：缓存中为找到id为4的记录，但也未执行查询语句，而是直接返回，说明，该次load直接采用了上次load的结果
}
Person p = (Person) s.get(Person.class, 4L);
System.out.println(s.get(Person.class, 4L));
//日志输出：Person [id=4, name=张三, age=12, birthDay=2014-08-29]
//分析：缓存中找到id为4的记录，直接返回，不执行查询语句。
System.out.println(s.load(Person.class, 4L));
//日志输出：Person [id=4, name=张三, age=12, birthDay=2014-08-29]
//分析：缓存中存在id为4的记录，直接返回，不执行查询语句
p.setAge(121212);
update(s, p);
System.out.println(s.get(Person.class, 4L));
//日志输出：Person [id=4, name=张三, age=121212, birthDay=2014-08-29]
//分析：没有执行查询语句，说明update时也同步更新了缓存中的记录
delete(s, p);
//日志输出：Hibernate: delete from person where pid=?
//分析：执行删除语句
try{
System.out.println(s.get(Person.class, 4L));
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
// null
//分析：在缓存中没有找到id为4的记录，执行查询语句，也未找到记录，返回Null
}
try{
System.out.println(s.load(Person.class, 4L));
//日志输出：Hibernate: select person0_.pid as pid0_0_, person0_.pname as pname0_0_, person0_.birthDay as birthDay0_0_, person0_.age as age0_0_ from person person0_ where person0_.pid=?
//分析： 缓存中未找到id为4的记录，执行查询语句
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
//日志输出：ObjectNotFoundException: No row with the given identifier exists: [hibernate.entity.Person#4]
//分析： 在数据库中也未找到id为4的记录，直接抛出异常
}
}catch(Exception e){
System.out.println(ExceptionUtils.getMessage(e));
}
}
