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：
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 {@Beanpublic 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@Autowiredprivate UserMapper userMapper;@Autowiredprivate OrderMapper orderMapper;@Autowiredprivate 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 value();
}
1.6 自定义fanctoryBean
public class CondorHeroFactoryBean implements FactoryBean {private Class mapperInterface;private SqlSession sqlSession;public CondorHeroFactoryBean(Class mapperInterface) {this.mapperInterface = 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();}@Overridepublic Object getObject() throws Exception {//动态代理获取UserMapper接口对象System.out.println("6.……getObject……");return sqlSession.getMapper(mapperInterface);}@Overridepublic Class<?> getObjectType() {return mapperInterface;}
}
1.7 自定义Bean注册类
public class CondorHeroImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {@Overridepublic 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() {@Overridepublic 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);}@Overrideprotected 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*/@Overrideprotected 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
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
2.3 在registerBeanDefinitions方法中注册一个MapperScannerConfigurer类型的BeanDefinition
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
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
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 = true;}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);}}
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> {}
@Overridepublic T getObject() throws Exception {return getSqlSession().getMapper(this.mapperInterface);}@Overridepublic 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：
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 {@Beanpublic 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
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。
@Autowiredprivate OrderMapper orderMapper;
即：这时候的orderMapper就 是赋值了代理对象的对象是有值 的。
