In-depth exploration of the operating mechanism and execution process of MyBatis

In-depth analysis of the working principle and process of MyBatis

MyBatis is a popular persistence layer framework used to simplify the interaction process with the database. It provides a flexible mapping mechanism that can map SQL statements to Java objects, and supports transaction management and caching mechanisms. This article will deeply analyze the working principle and process of MyBatis, and illustrate it through specific code examples.

1. The working principle of MyBatis

The working principle of MyBatis can be simply divided into two stages: the configuration stage and the running stage.

1. Configuration phase

In the configuration phase, MyBatis will read the configuration file (such as mybatis-config.xml) and mapping file (such as UserMapper.xml), and parse they. The configuration file contains configuration items such as database connection information, global settings, and type processors, while the mapping file defines the mapping relationship between SQL statements and Java methods.

2. Running phase

In the running phase, MyBatis first creates a SqlSessionFactory object based on the parsing results of the configuration phase, which is responsible for creating SqlSession instances. SqlSession is the core object for interacting with the database, through which we can execute SQL statements and obtain results.

2. The workflow of MyBatis

The workflow of MyBatis can be simply described as the following steps:

1. Loading the configuration file

First, MyBatis will load the configuration file (mybatis-config.xml). This file contains configuration items such as database connection information, global settings, and the path to the mapping file. When loading the configuration file, MyBatis will create a Configuration object, which saves all configuration information.

2. Parse the mapping file

Next, MyBatis will parse the mapping file (such as UserMapper.xml). The mapping file defines the mapping relationship between SQL statements and Java methods. MyBatis will parse the mapping file into MappedStatement objects, and each MappedStatement object represents the mapping relationship of a SQL statement.

3. Create SqlSessionFactory

According to the parsing results of the configuration phase, MyBatis will create a SqlSessionFactory object. SqlSessionFactory is one of the core interfaces of MyBatis, which is responsible for creating SqlSession objects.

4. Open SqlSession

Next, we need to create a SqlSession object using the SqlSessionFactory object. SqlSession is the core interface for MyBatis to interact with the database. It can execute SQL statements and return execution results. After using the SqlSession, you need to close it manually.

Code example:

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

SqlSession sqlSession = sqlSessionFactory.openSession();
try {
  // 调用SqlSession的方法执行SQL语句
  // ...
} finally {
  sqlSession.close();
}

5. Execute SQL statement

After obtaining the SqlSession object, we can execute the SQL statement through it. MyBatis provides a variety of ways to execute SQL statements, including selectOne, selectList, insert, update and delete methods. We only need to pass in the mapping ID and corresponding parameters corresponding to the SQL statement to execute the SQL statement and obtain the results.

Code example:

User user = sqlSession.selectOne("com.example.UserMapper.getUserById", 1);
System.out.println(user);

6. Submit transaction

If we enable transactions when executing SQL statements, then after all SQL statements are executed, The transaction needs to be committed manually.

Code example:

sqlSession.commit();

7. Close SqlSession

Finally, after using SqlSession, you need to manually close it and release resources.

Code example:

sqlSession.close();

3. Summary

This article provides an in-depth analysis of the working principle and process of MyBatis. The configuration phase mainly reads configuration files and parses mapping files, while the running phase creates SqlSessionFactory objects, through which SqlSession is created and SQL statements are executed. Through specific code examples, we can better understand the workflow of MyBatis and learn how to use it to simplify the interaction process with the database. I hope this article will help everyone understand MyBatis.

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