spring+mybaits xml配置解析----转

一、项目中spring+mybaits xml配置解析

一般我们会在datasource.xml中进行如下配置，但是其中每个配置项原理和用途是什么，并不是那么清楚，如果不清楚的话，在使用时候就很有可能会遇到坑，所以下面对这些配置项进行一一解说

（1）配置数据源
 <bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
        <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver" />
        <property name="url" value="${db_url}" />
        <property name="username" value="$db_user}" />
        <property name="password" value="${db_passwd}" />
        <property name="maxWait" value="${db_maxWait}" />
        <property name="maxActive" value="28" />
        <property name="initialSize" value="2" />
        <property name="minIdle" value="0" />
        <property name="timeBetweenEvictionRunsMillis" value="db_time" />
    </bean>

（2）创建sqlSessionFactory
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="mapperLocations" value="classpath*:com/**/mapper/*Mapper*.xml" />
        <property name="dataSource" ref="dataSource" />
        <property name="typeAliasesPackage" value="com.test.***.dal" />
</bean>

（3）配置扫描器，扫描指定路径的mapper生成数据库操作代理类
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
    <property name="annotationClass" value="javax.annotation.Resource"></property>
        <property name="basePackage" value="com.test.***.dal.***.mapper" />
        <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

（4）配置事务管理器
<bean id="transactionManager"
    class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource" />
</bean>

（5）声明使用注解式事务
<tx:annotation-driven transaction-manager="transactionManager" />
（6）注册各种beanfactory处理器
<context:annotation-config />    

（7）该配置创建了一个TransactionInterceptor的bean，作为事务切面的执行方法
 <tx:advice id="defaultTxAdvice">
    <tx:attributes>
        <tx:method name="*" rollback-for="Exception" />
    </tx:attributes>
</tx:advice>

（8）该配置创建了一个DefaultBeanFactoryPointcutAdvisor的bean，该bean是一个advisor,里面包含了pointcut和advice.前者说明切面加在哪里，后者是执行逻辑。此处可以配多个advisor
<aop:config>
    <aop:pointcut id="myCut" expression="(execution(* *..*BoImpl.*(..))) "/>
    <aop:advisor pointcut-ref="myCut" advice-ref="defaultTxAdvice" />
</aop:config>

1.1 数据源配置

(1）是数据源配置，这个没啥好说的。

1.2 配置SqlSessionFactory

(2) 作用是根据配置创建一个SqlSessionFactory，看下SqlSessionFactoryBean的代码知道它实现了FactoryBean和InitializingBean类，由于实现了InitializingBean，所以自然它的afterPropertiesSet方法，由于实现了FactoryBean类，所以自然会有getObject方法。下面看下时序图：

screenshot.png

从时序图可知，SqlSessionFactoryBean类主要是通过属性配置创建SqlSessionFactory实例，具体是解析配置中所有的mapper文件放到configuration,然后作为构造函数参数实例化一个DefaultSqlSessionFactory作为SqlSessionFactory。

1.3 配置扫描器，扫描指定路径的mapper生成数据库操作代理类

MapperScannerConfigurer 实现了 BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware接口，所以会重写一下方法：

1.3.1
//在bean注册到ioc后创建实例前修改bean定义和新增bean注册，这个是在context的refresh方法调用
void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
1.3.2
//在bean注册到ioc后创建实例前修改bean定义或者属性值
void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;
1.3.3
//set属性设置后调用
void afterPropertiesSet() throws Exception;
1.3.4
//获取IOC容器上下文，在context的prepareBeanFactory中调用
void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
1.3.5
//获取bean在ioc容器中名字，在context的prepareBeanFactory中调用
void setBeanName(String name);

先上个扫描mapper生成代理类并注册到ioc时序图：

screenshot.png

首先MapperScannerConfigurer实现的afterPropertiesSet方法用来确保属性basePackage不为空

public void afterPropertiesSet() throws Exception {
    notNull(this.basePackage, "Property 'basePackage' is required");
  }

postProcessBeanFactory里面啥都没做，setBeanName获取了bean的名字，setApplicationContext里面获取了ioc上下文。下面看重要的方法postProcessBeanDefinitionRegistry，由于mybais是运行时候才通过解析mapper文件生成代理类注入到ioc，所以postProcessBeanDefinitionRegistry正好可以干这个事情。

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

    //构造一个ClassPathMapperScanner查找mapper
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    scanner.setAddToConfig(this.addToConfig);
    //javax.annotation.Resource
    scanner.setAnnotationClass(this.annotationClass);
    scanner.setMarkerInterface(this.markerInterface);
    //引用sqlSessionFactory
    scanner.setSqlSessionFactory(this.sqlSessionFactory);
    scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
    scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
    scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
    //ioc上下文
    scanner.setResourceLoader(this.applicationContext);
    scanner.setBeanNameGenerator(this.nameGenerator);
    scanner.registerFilters();
   //basePackage=com.alibaba.***.dal.***.mapper,com.alibaba.rock.auth.mapper,com.alibaba.rock.workflow.dal.workflow.mapper
    scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

下面重点看下scan方法：

 public Set<BeanDefinitionHolder> doScan(String... basePackages) {
    //根据指定路径去查找对应mapper的接口类，并转化为beandefination
    Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

    if (beanDefinitions.isEmpty()) {
      logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
    } else {
      //修改接口类bean的beandefination
      processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
  }

其中super.doScan(basePackages);根据指定路径查找mapper接口类，并生成bean的定义对象，对象中包含beanclassname,beanclass属性，最后注册该bean到ioc容器。下面看下最重要的processBeanDefinitions方法对bean定义的改造。

 private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (GenericBeanDefinition) holder.getBeanDefinition();

      // 上面讲的扫描后beanclass设置的为mapper接口类，但是这里修改为MapperFactoryBean，MapperFactoryBean代理了mapper接口类,并且实际mapper接口类作为构造函数传入了      definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName());
      definition.setBeanClass(this.mapperFactoryBean.getClass());
      definition.getPropertyValues().add("addToConfig", this.addToConfig);

      //设置属性配置中的sqlSessionFactory
      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);
      }
    }
  }

注：这里修改了mapper接口类的beandefination中的beanclass为MapperFactoryBean，它则负责生产数据类操作代理类，实际mapper接口类作为构造函数传入了 。由于只修改了beanclass,没有修改beanname，所以我们从容器中获取时候无感知的。

在上一个代理bean如何构造的时序图：

screenshot.png

下面看下MapperFactoryBean是如何生成代理类的:
首先，上面代码设置了MapperFactoryBean的setSqlSessionFactory方法：

  public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (!this.externalSqlSession) {
      this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
    }
  }

上面方法创建了sqlSession，由于MapperFactoryBean为工厂bean所以实例化时候会调用getObject方法：

 public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }

其实是调用了SqlSessionTemplate->getMapper,其中mapperInterface就是创建MapperFactoryBean时候的构造函数参数。

public <T> T getMapper(Class<T> type) {
    return getConfiguration().getMapper(type, this);
  }

这里调用getConfiguration().getMapper(type, this);实际是DefaultSqlSessionFactory里面的configration的getMapper方法:

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
   //knownMappers是上面时序图中步骤6设置进入的。
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) 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);
    }
  }
 protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
   //代理回调类为MapperProxy
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

在上一个实际执行sql时候调用代理类的序列图：

screenshot.png

所以当调用实际的数据库操作时候会调用MapperProxy的invoke方法：

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

mapperMethod.execute(sqlSession, args);里面实际是调用当前mapper对应的SqlSessionTemplate的数据库操作，而它有委托给了代理类sqlSessionProxy，sqlSessionProxy是在SqlSessionTemplate的构造函数里面创建的：

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
    notNull(executorType, "Property 'executorType' is required");

    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }

所以最终数据库操作有被代理SqlSessionInterceptor执行：

 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      //有TransactionSynchronizationManager管理
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
          .....
      }
    }

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sessionFactory, NO_SQL_SESSION_FACTORY_SPECIFIED);
    notNull(executorType, NO_EXECUTOR_TYPE_SPECIFIED);

    SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

    SqlSession session = sessionHolder(executorType, holder);
    if (session != null) {
      return session;
    }

    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("Creating a new SqlSession");
    }
   //这里看到了使用sessionfactory熟悉的打开了一个session
    session = sessionFactory.openSession(executorType);

    registerSessionHolder(sessionFactory, executorType, exceptionTranslator, session);

    return session;
  }

注意：这里3里面配置的扫描文件在4的扫描文件里面一定要有，因为3给每个扫描文件生成了一个代理，如果4里面多了一个mapper，那么在4中将找不到。

1.4 配置事务管理器

事务管理器作用见名知意，是用来管理事务的。

1.5 advice配置

作用是创建了一个TransactionInterceptor的bean，作为事务切面的执行方法。标签解析的流程图：

screenshot.png

由于是tx标签，自然要查找TxNamespaceHandler，代码如下：

public class TxNamespaceHandler extends NamespaceHandlerSupport {

    static final String TRANSACTION_MANAGER_ATTRIBUTE = "transaction-manager";
    static final String DEFAULT_TRANSACTION_MANAGER_BEAN_NAME = "transactionManager";

    static String getTransactionManagerName(Element element) {
        return (element.hasAttribute(TRANSACTION_MANAGER_ATTRIBUTE) ?
                element.getAttribute(TRANSACTION_MANAGER_ATTRIBUTE) : DEFAULT_TRANSACTION_MANAGER_BEAN_NAME);
    }

    @Override
    public void init() {
        registerBeanDefinitionParser("advice", new TxAdviceBeanDefinitionParser());
        registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
        registerBeanDefinitionParser("jta-transaction-manager", new JtaTransactionManagerBeanDefinitionParser());
    }

}

从init方法知道advice标签需要TxAdviceBeanDefinitionParser这个解析类。
结合流程图第一步设置了事务管理器的引用，我们看下引用的bean的名字：

static final String DEFAULT_TRANSACTION_MANAGER_BEAN_NAME = "transactionManager";

static String getTransactionManagerName(Element element) {
        return (element.hasAttribute(TRANSACTION_MANAGER_ATTRIBUTE) ?
                element.getAttribute(TRANSACTION_MANAGER_ATTRIBUTE) : DEFAULT_TRANSACTION_MANAGER_BEAN_NAME);
    }

可以知道如果没有配置这个属性，那么默认查找依赖beanname=transactionManager。
然后parseAttributeSource主要循环解析我们配置的method标签，和设置的方法的事务属性。
另外代码：

protected Class<?> getBeanClass(Element element) {
        return TransactionInterceptor.class;
    }

可以知道这个advice标签实际是创了TransactionInterceptor对象，并且通过调用setTransactionManager设置了事务管理器，通过setTransactionAttributeSources设置了事务属性。

1.6 设置advisor

标签<aop:config>作用是创建了DefaultBeanFactoryPointcutAdvisor作为拦截器，把满足切点的bean进行代理使用事务拦截器进行拦截。具体标签逻辑先看流程图：

screenshot.png

从标签<aop:config>可知要查找AopNamespaceHandler,代码如下：

public class AopNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
        registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
        registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());

        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
    }
}

可知config标签是ConfigBeanDefinitionParser来解析的，根据流程图知configureAutoProxyCreator注册了AspectJAwareAdvisorAutoProxyCreator类，然后createAdvisorBeanDefinition创建了DefaultBeanFactoryPointcutAdvisor，它是个advisor,并且设置引用了advice,这个adivce就是上面1.5讲解的，然后createPointcutDefinition创建了切点AspectJExpressionPointcut，最后把切点设置到了advisor。
DefaultBeanFactoryPointcutAdvisor作用就是对满足pointcut表达式的类的方法进行代理，并且使用advice进行拦截处理，而advice就是事务拦截器。

1.7 设置注解式事务

上面介绍完后就可以使用事务切面了，但是有时候还需要在具体类或者方法上进行注解行事务，那么这就需要加 <tx:annotation-driven transaction-manager=”transactionManager” />配置
先上时序图：

screenshot.png

!
同理1.6 不同是这里创建了advisor,设置了advice（事务拦截器），但是好像没有设置pointcut，看下BeanFactoryTransactionAttributeSourceAdvisor源码知道：

public class BeanFactoryTransactionAttributeSourceAdvisor extends AbstractBeanFactoryPointcutAdvisor {

    private TransactionAttributeSource transactionAttributeSource;

    private final TransactionAttributeSourcePointcut pointcut = new TransactionAttributeSourcePointcut() {
        @Override
        protected TransactionAttributeSource getTransactionAttributeSource() {
            return transactionAttributeSource;
        }
    };
}

直接内置了pointcut,只不过1.6是AspectJExpressionPointcut表达式的切点，这里是注解。
那么这个BeanFactoryTransactionAttributeSourceAdvisor什么时候被用来增强注解事务的类那，那是InfrastructureAdvisorAutoProxyCreator所做的事情，InfrastructureAdvisorAutoProxyCreator是个BeanPostProcessor，会在bean创建初始化后时候调用postProcessAfterInitialization，就是这个方法。

另外注意如果配置了多个注解式标签在datasource.xml里面时候只有第一个生效

public static void configureAutoProxyCreator(Element element, ParserContext parserContext) {
            AopNamespaceUtils.registerAutoProxyCreatorIfNecessary(parserContext, element);

            String txAdvisorBeanName = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME;
            //如果配置了多个注解式标签在datasource.xml里面时候只有第一个生效
            if (!parserContext.getRegistry().containsBeanDefinition(txAdvisorBeanName)) {
                Object eleSource = parserContext.extractSource(element);

                // Create the TransactionAttributeSource definition.
                RootBeanDefinition sourceDef = new RootBeanDefinition(
                        "org.springframework.transaction.annotation.AnnotationTransactionAttributeSource");
                sourceDef.setSource(eleSource);
                sourceDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
                String sourceName = parserContext.getReaderContext().registerWithGeneratedName(sourceDef);

                // Create the TransactionInterceptor definition.
                RootBeanDefinition interceptorDef = new RootBeanDefinition(TransactionInterceptor.class);
                interceptorDef.setSource(eleSource);
                interceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
                registerTransactionManager(element, interceptorDef);
                interceptorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
                String interceptorName = parserContext.getReaderContext().registerWithGeneratedName(interceptorDef);

                // Create the TransactionAttributeSourceAdvisor definition.
                RootBeanDefinition advisorDef = new RootBeanDefinition(BeanFactoryTransactionAttributeSourceAdvisor.class);
                advisorDef.setSource(eleSource);
                advisorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
                advisorDef.getPropertyValues().add("transactionAttributeSource", new RuntimeBeanReference(sourceName));
                advisorDef.getPropertyValues().add("adviceBeanName", interceptorName);
                if (element.hasAttribute("order")) {
                    advisorDef.getPropertyValues().add("order", element.getAttribute("order"));
                }
                parserContext.getRegistry().registerBeanDefinition(txAdvisorBeanName, advisorDef);

                CompositeComponentDefinition compositeDef = new CompositeComponentDefinition(element.getTagName(), eleSource);
                compositeDef.addNestedComponent(new BeanComponentDefinition(sourceDef, sourceName));
                compositeDef.addNestedComponent(new BeanComponentDefinition(interceptorDef, interceptorName));
                compositeDef.addNestedComponent(new BeanComponentDefinition(advisorDef, txAdvisorBeanName));
                parserContext.registerComponent(compositeDef);
            }
        }

1.8 注册各种beanfactory处理器

当我们需要使用BeanPostProcessor时，最直接的使用方法是在Spring配置文件中定义这些Bean。单这些会显得比较笨拙，
例如：使用@Autowired注解，必须事先在Spring容器中声明

<bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor "/>

使用 @Required注解，就必须声明：

<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>

通过标签<context:annotation-config/> ，我们可以同时自动注册这些常用的beanfactory处理器，避免了我们一个个配置的繁琐步骤:

public class ContextNamespaceHandler extends NamespaceHandlerSupport {

                ...
        registerJava5DependentParser("annotation-config",
                "org.springframework.context.annotation.AnnotationConfigBeanDefinitionParser");
        ....
}

public class AnnotationConfigBeanDefinitionParser implements BeanDefinitionParser {

    public BeanDefinition parse(Element element, ParserContext parserContext) {
                ...
        // Obtain bean definitions for all relevant BeanPostProcessors.
        Set<BeanDefinitionHolder> processorDefinitions =
                AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);

        // Register component for the surrounding <context:annotation-config> element.
        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
        parserContext.pushContainingComponent(compDefinition);

        // Nest the concrete beans in the surrounding component.
        for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
            parserContext.registerComponent(new BeanComponentDefinition(processorDefinition));
        }

        // Finally register the composite component.
        parserContext.popAndRegisterContainingComponent();

        return null;
    }

}

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
            BeanDefinitionRegistry registry, Object source) {

        Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>(4);

        // Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
        if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition();
            try {
                ClassLoader cl = AnnotationConfigUtils.class.getClassLoader();
                def.setBeanClass(cl.loadClass(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME));
            }
            catch (ClassNotFoundException ex) {
                throw new IllegalStateException(
                        "Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
            }
            def.setSource(source);
            def.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            beanDefinitions.add(registerBeanPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
        if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
            def.setSource(source);
            def.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            beanDefinitions.add(registerBeanPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
            def.setSource(source);
            def.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            beanDefinitions.add(registerBeanPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        if (!registry.containsBeanDefinition(REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
            RootBeanDefinition def = new RootBeanDefinition(RequiredAnnotationBeanPostProcessor.class);
            def.setSource(source);
            def.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
            beanDefinitions.add(registerBeanPostProcessor(registry, def, REQUIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
        }

        return beanDefinitions;
    }

主要注册常用的：
RequiredAnnotationBeanPostProcessor
AutowiredAnnotationBeanPostProcessor
CommonAnnotationBeanPostProcessor
平时我们使用autowired或者required之所以能生效，就是因为这个自动注入ioc已经。

原文地址：

http://ifeve.com/spring%E4%BA%8B%E5%8A%A1%E9%85%8D%E7%BD%AE%E8%A7%A3%E6%83%91/