mapper接口代理对象创建原理

springboot整合mybatis

    org.mybatis.spring.boot
    mybatis-spring-boot-starter
    1.3.2

mapper接口代理对象的创建

写在前面：Mapper接口对象时通过org.mybatis.spring.mapper.MapperFactoryBean#getObject方法创建的。

org.mybatis.spring.mapper.MapperFactoryBean#getObject
​
@Override
public T getObject() throws Exception {
  return getSqlSession().getMapper(this.mapperInterface);
}

自动配置类 （MybatisAutoConfiguration）

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter({ DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class })
public class MybatisAutoConfiguration implements InitializingBean {
​
    @Bean
    @ConditionalOnMissingBean
    public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
      // 通过SqlSessionFactoryBean对象的getObject创建SqlSessionFactory
      SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
    ........
      return factory.getObject();
    }
    
  // 创建 SqlSessionTemplate对象 
  @Bean
  @ConditionalOnMissingBean
  public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
    ExecutorType executorType = this.properties.getExecutorType();
    if (executorType != null) {
      return new SqlSessionTemplate(sqlSessionFactory, executorType);
    } else {
      return new SqlSessionTemplate(sqlSessionFactory);
    }
  }
}

org.mybatis.spring.SqlSessionFactoryBean#getObject

class : org.mybatis.spring.SqlSessionFactoryBean
​
@Override
public SqlSessionFactory getObject() throws Exception {  
  if (this.sqlSessionFactory == null) {
     // 会创建 configLocation对象作为sqlSessionFactory的属性
    afterPropertiesSet();
  }
  return this.sqlSessionFactory;
}
​
@Override
public void afterPropertiesSet() throws Exception {
    // 创建sqlSessionFactory
    this.sqlSessionFactory = buildSqlSessionFactory();
}
​
protected SqlSessionFactory buildSqlSessionFactory() throws Exception {
  final Configuration targetConfiguration;
   ..........
  return this.sqlSessionFactoryBuilder.build(targetConfiguration);
}

class: org.apache.ibatis.session.SqlSessionFactoryBuilder#build(org.apache.ibatis.session.Configuration)
​
public SqlSessionFactory build(Configuration config) {
   // SqlSessionFactory实质是 DefaultSqlSessionFactory
  return new DefaultSqlSessionFactory(config);
}

小结：自动配置类中，创建两大对象（DefaultSqlSessionFactory和SqlSessionTemplate），交给spring容器管理。

SqlSessionFactory（DefaultSqlSessionFactory）创建过程：解析mapper.xml,创建configuration对象，交给SqlSessionFactory对象。configuration是DefaultSqlSessionFactory对象的属性。

 

注解@MapperScan

@Import(MapperScannerRegistrar.class)
public @interface MapperScan {
    ...... 
}

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {}

说明：MapperScan注解中，是通过import注解导入MapperScannerRegistrar.class。而MapperScannerRegistrar（Mapper扫描注册器）实现了ImportBeanDefinitionRegistrar接口。所以spring启动时，会调用该接口的registerBeanDefinitions方法给spring容器注册bean definitions。也就是个beanDefinitonMap中加入beanDefinition

 

MapperScannerRegistrar#registerBeanDefinitions分析

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
​
  private ResourceLoader resourceLoader;
​
  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
​
    AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    ......
    // 扫描
    scanner.doScan(StringUtils.toStringArray(basePackages));
  }
}
​

org.mybatis.spring.mapper.ClassPathMapperScanner#doScan

// 扫描类 ---> 创建BeanDefinitions ---> 注册到beanDefinionMap中 ---> 修改BeanDefinitions

class: org.mybatis.spring.mapper.ClassPathMapperScanner extends ClassPathBeanDefinitionScanner
​
@Override
public Set doScan(String... basePackages) {
  // 通过指定的包路径，扫描mapper接口，创建BeanDefinition
  Set beanDefinitions = super.doScan(basePackages);
    .......
  processBeanDefinitions(beanDefinitions);
    .......
  return beanDefinitions;
}

org.mybatis.spring.mapper.ClassPathMapperScanner#processBeanDefinitions

   
private MapperFactoryBean mapperFactoryBean = new MapperFactoryBean