In-depth analysis of MyBatis caching mechanism: exploring first-level cache and second-level cache

MyBatis is an excellent persistence layer framework that provides a rich caching mechanism, including first-level cache and second-level cache. This article will comprehensively analyze the caching mechanism of MyBatis from the first level cache to the second level cache, and provide specific code examples.

First-level cache

MyBatis's first-level cache is a SqlSession-based cache, also called a local cache. When executing the same SQL statement and passing in the same parameters, MyBatis will cache the query results in the SqlSession to avoid repeated queries to the database and improve query performance.

By default, the first level cache is enabled. But in the first-level cache, it will only take effect when the same SQL statement is executed in the same SqlSession. If the same SQL statement is executed in different SqlSession, the first-level cache will not hit.

The following is a sample code for the first-level cache:

// 获取 SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();

// 执行查询
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
User user1 = userMapper.getUserById(1);
User user2 = userMapper.getUserById(1);

// 关闭 SqlSession
sqlSession.close();

In the above example, the first time the getUserById method is executed, the query results will be cached in the SqlSession , the second time the same SQL statement is executed, the results will be obtained directly from the first-level cache.

Second level cache

The second level cache is a cache based on SqlSessionFactory, also known as the global cache. When executing the same SQL statement in different SqlSession, the second-level cache can be used to avoid repeated queries to the database and improve query performance.

The second-level cache needs to be configured and enabled in the MyBatis configuration file, and the corresponding Mapper interface needs to be configured for caching. At the same time, it should be noted that the entity object needs to implement the serialization interface so that it can be transmitted between different SqlSession.

The following is a sample code for the second-level cache:

// 开启二级缓存
<mapper namespace="com.example.mapper.UserMapper">
    <cache/>
</mapper>

// 获取 SqlSession
SqlSession sqlSession1 = sqlSessionFactory.openSession();
UserMapper userMapper1 = sqlSession1.getMapper(UserMapper.class);
User user1 = userMapper1.getUserById(1);
sqlSession1.close();

// 开启新的 SqlSession
SqlSession sqlSession2 = sqlSessionFactory.openSession();
UserMapper userMapper2 = sqlSession2.getMapper(UserMapper.class);
User user2 = userMapper2.getUserById(1);
sqlSession2.close();

In the above example, the first execution of the getUserById method will cache the query results in the second-level cache , the second time the same SQL statement is executed, the results will be obtained directly from the second-level cache.

Summary

The caching mechanism of MyBatis provides two caching methods: first-level cache and second-level cache, which can effectively improve query performance and avoid repeated queries to the database. In actual development, the appropriate caching method can be selected according to the application situation to optimize performance.

We hope that the introduction of this article can help readers fully understand the caching mechanism of MyBatis and apply it flexibly in actual projects.

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