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));
		}
	}