Mybatis中缓存

1、一级缓存

SqlSession sqlSession = SqlSessionUtils.getSqlSession();CacheMapper mapper = sqlSession.getMapper(CacheMapper.class);Emp emp1 = mapper.getEmpByEid(1);System.out.println(emp1);Emp emp2 = mapper.getEmpByEid(1);System.out.println(emp2);

可以看到只访问了一次数据库（因为只有一条sql语句记录）

SqlSession sqlSession = SqlSessionUtils.getSqlSession();CacheMapper mapper1 = sqlSession.getMapper(CacheMapper.class);CacheMapper mapper2 = sqlSession.getMapper(CacheMapper.class);Emp emp1 = mapper1.getEmpByEid(1);Emp emp2 = mapper2.getEmpByEid(1);System.out.println(emp1);System.out.println(emp2);

一样的结果

但是此情况下：

 SqlSession sqlSession1 = SqlSessionUtils.getSqlSession();SqlSession sqlSession2 = SqlSessionUtils.getSqlSession();CacheMapper mapper = sqlSession1.getMapper(CacheMapper.class);Emp emp1 = mapper.getEmpByEid(1);CacheMapper mapper1 = sqlSession2.getMapper(CacheMapper.class);Emp emp2 = mapper1.getEmpByEid(1);System.out.println(emp1);System.out.println(emp2);

可以看到访问了2次数据库，因为我们创建了两个sqlSession

因此可以看到一级缓存的范围在同一个sqlSession下。

2、使一级缓存失效

在中间增加一个添加操作

 SqlSession sqlSession = SqlSessionUtils.getSqlSession();CacheMapper mapper = sqlSession.getMapper(CacheMapper.class);Emp emp1 = mapper.getEmpByEid(1);System.out.println(emp1);int result = mapper.insertEmp(new Emp(null, "ab", 21, "女", "ab@qq.com"));System.out.println(result);Emp emp2 = mapper.getEmpByEid(1);System.out.println(emp2);

可以看到访问了三次，说明一级缓存失效了。

2、二级缓存

1）二级缓存的实现

（1）添加cache标签

（2）对应的实体类序列化

  try {InputStream is = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);SqlSession sqlSession1 = sqlSessionFactory.openSession(true);CacheMapper mapper1 = sqlSession1.getMapper(CacheMapper.class);Emp emp1 = mapper1.getEmpByEid(1);System.out.println(emp1);sqlSession1.close();SqlSession sqlSession2 = sqlSessionFactory.openSession();CacheMapper mapper2 = sqlSession2.getMapper(CacheMapper.class);Emp emp2 = mapper2.getEmpByEid(1);System.out.println(emp2);} catch (IOException e) {e.printStackTrace();}}

一个SqlSessionFactory建立了sqlSession1和sqlSession2

注意当缺sqlSession1.close()或是sqlSession1.commit() 不会实现二级缓存，不满足条件c