MyBatis實現註冊及獲取Mapper

2022-03-29 19:00:02

一、搭建環境

1.1 pom.xml

 <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
        </dependency>

1.2 BlogMapper.java

public interface BlogMapper {
    List<Blog> selectBlog(String id);
}

1.3 BlogMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mybatis.source.study.BlogMapper">
    <select id="selectBlog" resultType="mybatis.source.study.Blog">
    select * from t_blog where id= #{id}
  </select>
</mapper>

BlogMapper.xml放在resource目錄下與BlogMapper.java包路徑相同的路徑下

1.4 MyBatisDemo.java

public class MyBatisDemo {
    public static void main(String[] args) {
    	//建立資料來源
        DataSource dataSource = getDataSource();
        TransactionFactory transactionFactory = new JdbcTransactionFactory();
        //建立sql執行環境
        Environment environment = new Environment("development", transactionFactory, dataSource);
        //建立mybatis的所有設定
        Configuration configuration = new Configuration(environment);
        //註冊mapper
        configuration.addMapper(BlogMapper.class);
//        configuration.addInterceptor(new PaginationInterceptor());
		//根據設定建立sql對談工廠
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(configuration);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);
        System.out.println(mapper.selectBlog("001"));
    }

    private static DataSource getDataSource() {
        DruidDataSource druidDataSource = new DruidDataSource();
        druidDataSource.setUrl("jdbc:mysql://localhost:3306/demo?characterEncoding=utf-8&serverTimezone=Asia/Shanghai");
        druidDataSource.setUsername("root");
        druidDataSource.setPassword("root");
        return druidDataSource;
    }

二、addMapper詳細分析

2.1 MapperRegistry

這塊就是判斷這個mapper.xml解析過沒有，解析是在 parser.parse();中做的，來看

loadXmlResource();根據xml解析每個mapper介面的方法，將得到的MapperStatement放進了configuration，然後記錄該xml的namespace表示已經處理過。具體呼叫鏈：

loadXmlResource()–>xmlParser.parse()–>configurationElement(parser.evalNode("/mapper"))–> buildStatementFromContext(context.evalNodes(“select|insert|update|delete”))–> buildStatementFromContext(list, null)–>statementParser.parseStatementNode()–>builderAssistant.addMappedStatement–>configuration.addMappedStatement(statement);