spring整合mybatis的底层原理分析

2025-05-21 10:06 开发作者：神雕大侠mu

spring整合mybatis的底层原理

原理：

FactoryBean的自定义对象
jdk动态代理Mapper接口对象

一、手写一个spring集成mybatis

目录结构：

spring整合mybatis的底层原理分析

1.1 入口类

public class Test {
    public static void main(String[] args) {

        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        context.register(AppConfig.class);
        context.refresh();

        UserService userService = (UserService)context.getBean("userService");
        userService.test();
    }
}

1.2 配置类

@CondorHeroMapperScan("com.athome.tulin.springmybatis.mapper")
@ComponentScan("com.athome.tulin.springmybatis")
public class AppConfig {
    @Bean
    public SqlSessionFactory sqlSessionFactory() throws IOException {
        System.out.println("4.依赖注入MemberMapper需要先创建对象………AppConfig…………SqlSessionFactory………");
        InputStream inputStream = Resources.getResourceAsStream("mybatis.XML");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }
}

1.3 业务类

@Component
public class UserService {

    public UserService() {
        System.out.println("3.…………创建UserService…………");
    }

    //如何把mybatis生成的UserMapper的代理对象赋值给UserMapper
    @Autowired
    private UserMapper userMapper;

    @Autowired
    private OrderMapper orderMapper;

    @Autowired
    private MemberMapper memberMapper;

    public void test(){
        System.out.println("7.……UserService…test…");
        System.out.println(userMapper.selectById());
        System.out.println(orderMapper.selectById());
        System.out.println(memberMapper.selectById());
    }
}

1.4 创建3个Mapper接口

public interface MemberMapper {

    @Select("select 'member' ")
    String selectById();
}

public interface OrderMapper {
    @Select("select 'order' ")
    String selectById();
}

public interface UserMapper {
    @Select("select 'user' ")
    String selectById();
}

1.5 自定义注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Import(CondorHeroImportBeanDefinitionRegistrar.class)
public @interface CondorHeroMapperScan {
    String www.devze.comvalue();
}

1.6 自定义fanctoryBean

public class CondorHeroFactoryBean implements FactoryBean {
    
    private Class mapperInterface;

    private SqlSession sqlSession;
    public CondorHeroFactoryBean(Class mapperInterface) {
        this.mapperInterfajsce = mapperInterface;
    }
    /**
     * 从容器查找SqlSessionFactory 并获取sqlSession 赋值于sqlSession
     * 扫描的时候有 beanDefinition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
     * 那他就会自动找set方法
     * @param sqlSessionFactory
     */
    public void setSqlSession(SqlSessionFactory sqlSessionFactory) {
        System.out.println("5.……setSqlSession……");
        sqlSessionFactory.getConfiguration().addMapper(mapperInterface);
        this.sqlSession = sqlSessionFactory.openSession();
    }
    
    @Override
    public Object getObject() throws Exception {
        //动态代理获取UserMapper接口对象
        System.out.println("6.……getObject……");

       return sqlSession.getMapper(mapperInterface);
    }

    @Override
    public Class<?> getObjectType() {
        return mapperInterface;
    }
}

1.7 自定义Bean注册类

public class CondorHeroImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry, BeanNameGenerator importBeanNameGenerator) {
        System.out.println("1.……registerBeanDefinitions……");
        //1.获取注解上的指定路径
        Map<String, Object> annotationAttributes = importingClassMetadata.getAnnotationAttributes(CondorHeroMapperScan.class.getName());
        String path = (String)annotationAttributes.get("value");
        //2.扫描
        CondorHeroBeanDefinitionScanner scanner = new CondorHeroBeanDefinitionScanner(registry);
       scanner.addIncludeFilter(new TypeFilter() {
           @Override
           public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
               return true;
           }
       });

        scanner.scan(path);
    }
}

1.8 自定义扫描类

public class CondorHeroBeanDefinitionScanner extends ClassPathBeanDefinitionScanner {
    public CondorHeroBeanDefinitionScanner(BeanDefinitionRegistry registry) {
        super(registry);
    }

    @Override
    protected boolean isCandidateComponent(AnnotatedBeanDefinition beanDefinition)  {
        //只关心接口(判断是否是接口)
       return beanDefinition.getMetadata().isInterface();
    }

    /**
     * 扫描路径并得到beanDefinition
     * @param basePackages
     * @return
     */
    @Override
    protected Set<BeanDefinitionHolder> DOScan(String... basePackages) {
        System.out.println("2.……doScan……");
        Set<BeanDefinitionHolder> beanDefinitionHolders = super.doScan(basePackages);

        for (BeanDefinitionHolder beanDefinitionHolder: beanDefinitionHolders) {
            GenericBeanDefinition beanDefinition = (GenericBeanDefinition)beanDefinitionHolder.getBeanDefinition();
            //设置值
            beanDefinition.getConstructorArgumentValues().addGenericArgumentValue(beanDefinition.getBeanClassName());
            //设置名称
            beanDefinition.setBeanClassName(CondorHeroFactoryBean.class.getName());

            //将MapperFactoryBean的注入模型设置为By-Type。也就是说，MapperFactoryBean中的setXxx中的属性会从容器中来进行查找
            beanDefinition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
        }
        return beanDefinitionHolders;
    }
}

运行结果是:
1.……registerBeanDefinitions……
2.……doScan……
3.…………创建UserService…………
4.依赖注入MemberMapper需要先创建对象………AppConfig…………SqlSessionFactory………
5.……setSqlSession……
6.……getObject……
5.……setSqlSession……
6.……getObject……
5.……setSqlSession……
6.……getObject……
7.……UserService…test… user order member

二、原理解析

2.1 通过@MapperScan导入了MapperScannerRegistrar类

spring整合mybatis的底层原理分析

2.2 MapperScannerRegistrar类实现了ImportBeanDefinitionRegistrar接口，所以Spring在启动时会调用MapperScannerRegistrar类中的registerBeanDefinitions方法

spring整合mybatis的底层原理分析

2.3 在registerBeanDefinitions方法中注册一个MapperScannerConfigurer类型的BeanDefinition

spring整合mybatis的底层原理分析

2.4 而MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor接口，所以Spring在启动过程中时会调用它的postProcessBeanDefinitionRegistry()方法

spring整合mybatis的底层原理分析

2.5 在postProcessBeanDefinitionRegistry方法中会生成一个ClassPathMapperScanner对象，然后进行扫描(scanner.scan)2.6 通过利用Spring的扫描后，会把接口扫描出来并且得到对应的BeanDefinition

spring整合mybatis的底层原理分析

2.7 接下来把扫描得到的BeanDefinition进行修改，把BeanClass修改为MapperFactoryBean，把AutowireMode修改为byType(在类ClassPathMapperScanner的方法processBeanDefinitions中)

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (GenericBeanDefinition) holder.getBeanDefinition();
      String beanClassName = definition.getBeanClassName();
      LOGGER.debug(() -> "Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + beanClassName
          + "' mapperInterface");

      // the mapper interface is the original class of the bean
      // but, the actual class of the bean is MapperFactoryBean
      //设置值
      definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
      //设置名称
      definition.setBeanClass(this.mapperFactoryBeanClass);

      definition.getPropertyValues().add("addToConfig", this.addToConfig);

      boolean explicitFactoryUsed = false;
      if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
        definition.getPropertyValues().add("sqlSessionFactory",
            new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
        explicitFactoryUsed = true;
      } else if (this.sqlSessionFactory != null) {
        definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
        explicitFactoryUsed = true;
      }

      if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
        if (explicitFactoryUsed) {
          LOGGER.warn(
              () -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
        }
        definition.getPropertyValues().add("sqlSessionTemplate",
            new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
        explicitFactoryUsed = true;
      } else if (this.sqlSessionTemplate != null) {
        if (explicitFactoryUsed) {
          LOGGER.warn(
              () -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
        }
        definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
        explicitFactoryUsed =www.devze.com true;
   php   }

      if (!explicitFactoryUsed) {
        LOGGER.debug(() -> "Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
        //将MapperFactoryBean的注入模型设置为By-Type。也就是说，MapperFactoryBean中的setXxx中的属性会从容器中来进行查找
       definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
      definition.setLazyInit(lazyInitialization);javascript
    }
  }

2.8 扫描完成后，Spring就会基于BeanDefinition去创建Bean了，相当于每个Mapper对应一个FactoryBean

2.9 在MapperFactoryBean中的getObject方法中，调用了getSqlSession()去得到一个sqlSession对象，然后根据对应的Mapper接口生成一个Mapper接口代理对象，这个代理对象就成为Spring容器中的Bean

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {}

 @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }
  @Override
  public Class<T> getObjectType() {
    return this.mapperInterface;
  }

注意：这里的getObject调用时机是，在创建的对象依赖了Mapper对象就会去创建该Mapper对象，此时通过MapperFactoryBean去获取

2.10 sqlSession对象是Mybatis中的，一个sqlSession对象需要SqlSessionFactory来产生

上面的getSqlSession()对应源码是：

spring整合mybatis的底层原理分析

2.11 MapperFactoryBean的AutowireMode为byType，所以Spring会自动调用set方法，有两个set方法，一个setSqlSessionFactory，一个setSqlSessionTemplate，而这两个方法执行的前提是根据方法参数类型能找到对应的bean，所以Spring容器中要存在SqlSessionFactory类型的bean或者SqlSessionTemplate类型的bean

2.12 如果你定义的是一个SqlSessionFactory类型的bean，那么最终也会被包装为一个SqlSessionTemplate对象，并且赋值给sqlSession属性

这一步是程序员自己定义一个SqlSessionFactory，例如：

@CondorHeroMapperScan("com.athome.tulin.springmybatis.mapper")
@ComponentScan("com.athome.tulin.springmybatis")
public class AppConfig {
    @Bean
    public SqlSessionFactory sqlSessionFactory() throws IOException {
        System.out.println("4.依赖注入MemberMapper需要先创建对象………AppConfig…………SqlSessionFactory………");
        InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;
    }
}

这里定义的SqlSessionFactory 会赋值于2.10的sqlSessionTemplate

2.13 而在SqlSessionTemplate类中就存在一个getMapper方法，这个方法中就产生一个Mapper接口代理对象

spring整合mybatis的底层原理分析

2.14 当执行该代理对象的某个方法时，就会进入到Mybatis框架的底层执行流程

至此：业务类中的引入Mapper对象就复制成功。

 @Autowired
    private OrderMapper orderMapper;

即：这时候的orderMapper就是赋值了代理对象的对象是有值的。

总结

以上为个人经验，希望能给大家一个参考，也希望大家多多支持编程客栈(www.devze.com)。

继续阅读：mybatis底层原理 spring mybatis底层原理 spring整合mybatis的底层原理

spring整合mybatis的底层原理分析

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