MyBatis Spring整合源码解析

MapperScan源码分析？mapperScan如何生效的？

在项目中大多数用的都是@MapperScan注解，指定basePackages，扫描mybatis Mapper接口类,另外一种方式是用@Mapper注解，其实这两种方法扫描配置用的是一个地方，只是扫描入口不同。

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
//自动配置
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {
}

怎样让Spring 加载自己自定义的注解？

@MapperScan中加入Spring的注解@Import ,即导入一个配置类MapperScannerRegister,@MapperScan是根据其注解上MapperScannerRegistrar进行自动配置的，这个类会被Spring加载,Spring发现他实现了ImpoerBeanDefinitionRegistar这个接口，就会调用这个registerBeanDefinition的方法，顾名思义就是按照Spring的规则，注册自己的bean definition到Spring 的注册机中

怎样找到了mapper? 又是怎样将mapper 注册到 spring 容器中

下面就是自己实现的类扫描ClassPathMapperScanner，继承自Spring原生的ClassPathBeanDefinitionScanner

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {

  private ResourceLoader resourceLoader;

  /**
   * {@inheritDoc}
   */
  @Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    //拿到MapperScan类里面的属性
    AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
   //自定义注册机registry
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

    // this check is needed in Spring 3.1
    if (resourceLoader != null) {
      scanner.setResourceLoader(resourceLoader);
    }

    Class annotationClass = annoAttrs.getClass("annotationClass");
    if (!Annotation.class.equals(annotationClass)) {
      scanner.setAnnotationClass(annotationClass);
    }

    Class markerInterface = annoAttrs.getClass("markerInterface");
    if (!Class.class.equals(markerInterface)) {
      scanner.setMarkerInterface(markerInterface);
    }

    Class generatorClass = annoAttrs.getClass("nameGenerator");
    if (!BeanNameGenerator.class.equals(generatorClass)) {
      scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
    }

    Class mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
    if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
      scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
    }

    scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
    scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));

    List basePackages = new ArrayList();
    for (String pkg : annoAttrs.getStringArray("value")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
   //如果配置了包路径则将入进去
    for (String pkg : annoAttrs.getStringArray("basePackages")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
    for (Class clazz : annoAttrs.getClassArray("basePackageClasses")) {
      basePackages.add(ClassUtils.getPackageName(clazz));
    }
    scanner.registerFilters();
   //具体执行扫描
    scanner.doScan(StringUtils.toStringArray(basePackages));
  }
}

然后我们进入ClassPathMapperScanner#doScan方法调用父类ClassPathBeanDefinitionScanner#doScan来实现扫描并注册到spring ioc中，关于processBeanDefinitions方法后面我们会分析。

  public Set doScan(String... basePackages) {
    //调用父类ClassPathBeanDefinitionScanner#doScan来实现扫描并注册到spring ioc中
    Set beanDefinitions = super.doScan(basePackages);

    if (beanDefinitions.isEmpty()) {
      logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
    } else {
      processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
  }

	protected Set doScan(String... basePackages) {
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set beanDefinitions = new LinkedHashSet();
		for (String basePackage : basePackages) {
            //获取配置的路径下面所有的mapper全限定类名
			Set candidates = findCandidateComponents(basePackage);
			for (BeanDefinition candidate : candidates) {
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				//如果是基包下的一个抽象类，我们配置的mapper接口如果不是注解方式也会走这处理
				if (candidate instanceof AbstractBeanDefinition) {
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}

				//如果基包下的类是有注解的
				if (candidate instanceof AnnotatedBeanDefinition) {
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
            //是否beanName查看是否存在以及注册过
				if (checkCandidate(beanName, candidate)) {
                     //包装一下
					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
					definitionHolder =
							AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                    //加入到当前列表中
					beanDefinitions.add(definitionHolder);
                   //注册到IOC中
					registerBeanDefinition(definitionHolder, this.registry);
				}
			}
		}
		return beanDefinitions;
	}

我们使用MapperScan注解时，会将包路径一起设置进入。通过扫描MapperScan注解的类，通过AnnotationConfigUtils.processCommonDefinitionAnnotations来解析。然后包装为BeanDefinitionHolder，然后注册到Spring IOC里面

	protected boolean checkCandidate(String beanName, BeanDefinition beanDefinition) throws IllegalStateException {
//如果spring中没注册这个beanName对应的bean那么就是mybaits需要的类，一般mybaits的mapper类是一个接口不会被spring实例化加载到IOC容器中
		if (!this.registry.containsBeanDefinition(beanName)) {
			return true;
		}
//如果spring中有这个类的bean定义
		BeanDefinition existingDef = this.registry.getBeanDefinition(beanName);
		BeanDefinition originatingDef = existingDef.getOriginatingBeanDefinition();
		if (originatingDef != null) {
			existingDef = originatingDef;
		}

		//如果重复扫描此类或者或者重复获取同一个类的源文件或者是其它类的子类则是不兼容的，这样的类是不符合mybaits加载要求返回false
		if (isCompatible(beanDefinition, existingDef)) {
			return false;
		}
		throw new ConflictingBeanDefinitionException("Annotation-specified bean name '" + beanName +
				"' for bean class [" + beanDefinition.getBeanClassName() + "] conflicts with existing, " +
				"non-compatible bean definition of same name and class [" + existingDef.getBeanClassName() + "]");
	}

回过头来看看ClassPathMapperScanner#doScan#processBeanDefinitions方法

 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());

      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) {
        if (logger.isDebugEnabled()) {
          logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
        }
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
    }
  }

这就是开始注册自己的bean ,在这里发现获取到spring 给的后，类名没有修改，但是将类修改成了MapperFactoryBean, 即修改了具体的实现。通过构造器注入了原来的mapper的类名，下面开始往MapperFactoryBean里注入数据源等属性，这就是Spring bean 定义的修改器。
 

既然通过mapper类名这个ID, 找到的是MapperFactoryBean ，那这个类有什么用呢？

其实这个bean只是一个工厂方法,实现了Spring 定义的FactoryBean,所有得调用他的getObject()方法,才是真正注入的对象。

public class MapperFactoryBean extends SqlSessionDaoSupport implements FactoryBean {
     @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }
}

Spring发现这个bean是一个 工厂bean,会直接获取它真实的 bean.那这个sqlSession.getMapper(mapper接口类) 返回的对象是什么呢？

//sqlsession getMapper方法，返回Configuration的getMapper方法 
@Override
  public  T getMapper(Class type) {
    return configuration.getMapper(type, this);
  }

//Configuration getMapper方法
public  T getMapper(Class type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

发现每个Mapper 都映射成MapperProxyFactory,  顾名思义就是mapper的代理工厂，具体的对象就是返回一个代理对象

 protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

MapperProxy通过method找到mapperMethod，每个mapper 的方法都映射成一个MapperMethod.  MapperMethod 有sqlCommand ，有他来执行方法。

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    try {
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
      } else if (isDefaultMethod(method)) {
        return invokeDefaultMethod(proxy, method, args);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

最后调用execute方法转换成sqlSession执行对应的crud。所以mapper最后还是转到了SqlSession(Configuration,Executor具体执行者)

 

我们再来看看MapperFactoryBean的checkDaoConfig函数，看它是怎么将DAO关联到对应的mapper.xml的：

  @Override
  protected void checkDaoConfig() {

	//调用父类同名方法
    super.checkDaoConfig();

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

//获取sqlSessionFactoryBean中配置文件在java中的对象Configuration
    //如果没有mapperInterface的定义则加入此mapper的定义
    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Exception e) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
        throw new IllegalArgumentException(e);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }

这样Mapper接口就被注册到sqlSession中，每当操作sqlSession时就会根据这个mapperInterface去查找对应的mapper.xml构建mapper从而完成数据库操作。经过以上过程mybaits找到了所有mapper并将其加载到了spring ioc容器里。