mybatis - @MapperScan

一. 测试代码

 

 

//实体类
public class User   {
    private Integer id;
    private String name;
    private Integer age;
    private String email;
    private SexEnum sex;
    //getter / setter
}

public enum SexEnum {

    Male("Male", "男"),

    Female("Female", "女");

    private String code;

    private String desc;    

    SexEnum(String code, String desc){
        this.code = code;
        this.desc = desc;
    }   
}

//Repository
@Repository
public interface UserMapper  {

    public User getById(Integer id);

    public List getByAge(Integer age);

    public int insert(User user);
}

@SpringBootApplication
@MapperScan("com.study.demo.mybatis.mapper")
public class MybatisApplication {
    public static void main(String[] args) {
        SpringApplication.run(MybatisApplication.class, args);
    }    
}

@Test
public void getById(){
    System.out.println("getById 开始执行...");
    User user = userMapper.getById(1);
    System.out.println(user);
    System.out.println("getById 结束执行...");
}

mapper.xml文件:

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="com.study.demo.mybatis.mapper.UserMapper">
    <insert id="insert">
        insert into user (name,age,email,sex) values(#{name}, #{age}, #{email}, #{sex})
    insert>

    <select id="getById" resultType="com.study.demo.mybatis.vo.User">
        select * from user where id = #{id}
    select>

    <select id="getByAge" resultType="com.study.demo.mybatis.vo.User">
        select * from user where age = #{age}
    select>
mapper>

配置文件:

spring:
    datasource:
        #type: com.alibaba.druid.pool.DruidDataSource
        driver-class-name: com.mysql.jdbc.Driver
        url: jdbc:mysql://localhost:3306/deco?characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true&useSSL=false
        username: root
        password: 123456

mybatis:
    mapper-locations: classpath:mapper/**Mapper.xml

@MapperScan("com.study.demo.mybatis.mapper") 主要做了两件事情:

1. 根据 "com.study.demo.mybatis.mapper" 配置进行mapper.java文件扫描.

　　此处扫描到的就是 SchoolMapper.java 和 UserMapper.java 两个文件

2. 为扫描到的文件进行 BeanDefinition 注册

//关键代码: 
private void processBeanDefinitions(Set beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (GenericBeanDefinition) holder.getBeanDefinition();

      if (logger.isDebugEnabled()) {
        logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
          + "' and '" + definition.getBeanClassName() + "' mapperInterface");
      }

      // the mapper interface is the original class of the bean
      // but, the actual class of the bean is MapperFactoryBean
      definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
      definition.setBeanClass(this.mapperFactoryBean.getClass());
......
}

在进入此方法之前,  beanDefinitions 已经通过扫描得到, 

beanName	beanClass
schoolMapper	com.study.demo.mybatis.mapper.SchoolMapper
userMapper	com.study.demo.mybatis.mapper.UserMapper

进入方法后, 会执行以下代码, 对 beanClass 进行重新赋值:

definition.setBeanClass(this.mapperFactoryBean.getClass());

这里的 mapperFactoryBean 是 ClassPathMapperScanner 的一个私有属性:

private MapperFactoryBean mapperFactoryBean = new MapperFactoryBean