1革砸、概述

原生Mybatis源碼簡析(上)
原生Mybatis源碼簡析(下)
在介紹原生Mybatis源碼簡析文章中爆阶，我們知道泛粹，Mapper接口的生命周期是在方法級別，方法執(zhí)行結(jié)束器仗，Mapper接口的動態(tài)代理實(shí)現(xiàn)類的生命就終結(jié)了。在下一次執(zhí)行時童番，會再次重新生成新的代理類精钮。但是當(dāng)mybatis與spring結(jié)合使用時，mapper接口的代理實(shí)現(xiàn)類的生命周期是全局的剃斧，這是如何實(shí)現(xiàn)的呢轨香？首先在spring中引入mybatis時，是需要加入mybatis-spring包的引用的悯衬。在spring的xml配置中需要加入如下配置：

<!-- spring和MyBatis完美整合弹沽，不需要mybatis的配置映射文件 -->  
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
        <property name="dataSource" ref="dataSource" />  
        <!-- 自動掃描mapping.xml文件 -->  
        <property name="mapperLocations" value="classpath:com/javen/mapping/*.xml"></property>  
    </bean>  
  
    <!-- DAO接口所在包名檀夹，Spring會自動查找其下的類 -->  
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">  
        <property name="basePackage" value="com.javen.dao" />  
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>  
    </bean>  

那mapper接口的代理實(shí)現(xiàn)類的單例實(shí)現(xiàn)機(jī)制，定是與這兩個bean有關(guān)了策橘。

2炸渡、SqlSessionFactoryBean

SqlSessionFactoryBean，從名字就可看出他是一個FactoryBean丽已，如此就直接看起getObject方法

public SqlSessionFactory getObject() throws Exception {
    if (this.sqlSessionFactory == null) {
      afterPropertiesSet();
    }
    return this.sqlSessionFactory;
  }
public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
    state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
              "Property 'configuration' and 'configLocation' can not specified with together");

    this.sqlSessionFactory = buildSqlSessionFactory();
  }

在getObject方法中調(diào)用了afterPropertiesSet方法蚌堵，內(nèi)部又調(diào)用了buildSqlSessionFactory方法，該方法內(nèi)容很長沛婴，不再貼代碼了吼畏，但方法實(shí)現(xiàn)比較簡單，就是根據(jù)SqlSessionFactoryBean的眾多配置屬性來構(gòu)建出Configuration對象嘁灯，進(jìn)而實(shí)例化SqlSessionFactory對象泻蚊。與原廠mybatis的實(shí)現(xiàn)大同小異。

3丑婿、MapperScannerConfigurer

MapperScannerConfigurer類實(shí)現(xiàn)了BeanDefinitionRegistryPostProcessor接口性雄，則重點(diǎn)看下postProcessBeanDefinitionRegistry方法的實(shí)現(xiàn)

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }

    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    scanner.setAddToConfig(this.addToConfig);
    scanner.setAnnotationClass(this.annotationClass);
    scanner.setMarkerInterface(this.markerInterface);
    scanner.setSqlSessionFactory(this.sqlSessionFactory);
    scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
    scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
    scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
    scanner.setResourceLoader(this.applicationContext);
    scanner.setBeanNameGenerator(this.nameGenerator);
    scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
    scanner.registerFilters();
    scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

ClassPathMapperScanner類是mybatis-spring框架提供的類，實(shí)現(xiàn)了spring框架的ClassPathBeanDefinitionScanner類羹奉。

image.png

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
        Assert.notEmpty(basePackages, "At least one base package must be specified");
        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
        for (String basePackage : basePackages) {
            Set<BeanDefinition> 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);
                if (candidate instanceof AbstractBeanDefinition) {
                    postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
                }
                if (candidate instanceof AnnotatedBeanDefinition) {
                    AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
                }
                if (checkCandidate(beanName, candidate)) {
                    BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                    definitionHolder =
                            AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                    beanDefinitions.add(definitionHolder);
                    registerBeanDefinition(definitionHolder, this.registry);
                }
            }
        }
        return beanDefinitions;
    }

ClassPathBeanDefinitionScanner類的doScan方法會根據(jù)傳入的basePackage秒旋，掃描包下的所有.class文件，并根據(jù)該類文件生成相應(yīng)的BeanDefinition對象诀拭。針對mybatis的mapper接口迁筛，這里生成的BeanDefinition對象其實(shí)是半成品的對象，他的beanClass屬性是接口的全限定類名耕挨。然后將半成品的BeanDefinition對象集合返回细卧，在ClassPathMapperScanner類的processBeanDefinitions方法中，對這些半成品的BeanDefinition進(jìn)行二次加工俗孝。

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
      definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
      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() + "'.");
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
    }
  }

重點(diǎn)是definition.setBeanClass(this.mapperFactoryBeanClass);這段方法酒甸。

private Class<? extends MapperFactoryBean> mapperFactoryBeanClass = MapperFactoryBean.class;

MapperFactoryBean類也是一個FactoryBean，重置了beanClass屬性之后赋铝，此時的BeanDefinition就是一個成品的了插勤，之后實(shí)例化的時候，mapper接口對應(yīng)的對象就是MapperFactoryBean的實(shí)例革骨。如此便實(shí)現(xiàn)了mapper接口的全局單例話农尖。
有空得再看看源碼分析下，spring的事務(wù)是如何與mybatis的事務(wù)整合在一起的良哲？