本文主要是介绍Mybatis源码分析（3）—— 从Mybatis的视角去看Bean的初始化流程，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
不涉及Spring完整的启动流程，仅仅从Mybatis的视角去分析几个关键的方法，找到Mybatis是如何通过这几个扩展点植入进去的，反过来看Spring是如何设计，埋下这些伏笔，实现其可扩展性。
springContext-mybatis.xml的配置：
<!-- simplest possible SqlSessionFactory configuration -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="dataSource" ref="dataSource" /><property name="configLocation" value="classpath:/mybatis-config.xml"></property>
</bean><!-- Scan for mappers and let them be autowired; notice there is no UserDaoImplementation needed. The required SqlSessionFactory will be autowired. -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"><property name="basePackage" value="com.fcs.**.dao,fcs.common.**.dao" />
</bean>一般情况下，要植入进去，必须通过接口实现，这也是Spring的扩展点。SqlSessionFactoryBean和MapperScannerConfigurer分别实现了这些接口：
public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>,InitializingBean,ApplicationListener<ApplicationEvent> {
}public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {
}public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;}从AbstractApplicationContext的invokeBeanFactoryPostProcessors方法开始分析：
Map<String, BeanDefinitionRegistryPostProcessor> beanMap = beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans = new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());OrderComparator.sort(registryPostProcessorBeans);
for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {postProcessor.postProcessBeanDefinitionRegistry(registry);
}第一步：获取指定类型（BeanDefinitionRegistryPostProcessor）的beanMap
DefaultListableBeanFactory#getBeansOfType：
public <T> Map<String, T> getBeansOfType(Class<T> type, boolean includeNonSingletons, boolean allowEagerInit)throws BeansException {String[] beanNames = getBeanNamesForType(type, includeNonSingletons, allowEagerInit);Map<String, T> result = new LinkedHashMap<String, T>(beanNames.length);for (String beanName : beanNames) {try {result.put(beanName, getBean(beanName, type));}catch (BeanCreationException ex) {Throwable rootCause = ex.getMostSpecificCause();if (rootCause instanceof BeanCurrentlyInCreationException) {BeanCreationException bce = (BeanCreationException) rootCause;if (isCurrentlyInCreation(bce.getBeanName())) {if (this.logger.isDebugEnabled()) {this.logger.debug("Ignoring match to currently created bean '" + beanName + "': " +ex.getMessage());}onSuppressedException(ex);// Ignore: indicates a circular reference when autowiring constructors.// We want to find matches other than the currently created bean itself.continue;}}throw ex;}}return result;
}- String[] beanNames = getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
获取匹配类型的beanNames
- result.put(beanName, getBean(beanName, type));
根据名称和类型获取bean，放到result集合中
接下来会走bean的创建流程，在AbstractAutowireCapableBeanFactory的doCreateBean方法中：
// Initialize the bean instance.
Object exposedObject = bean;
try {populateBean(beanName, mbd, instanceWrapper);if (exposedObject != null) {exposedObject = initializeBean(beanName, exposedObject, mbd);}
}这里会调用MapperScannerConfigurer的afterPropertiesSet方法：
public void afterPropertiesSet() throws Exception {notNull(this.basePackage, "Property 'basePackage' is required");
}第二步：执行postProcessor的postProcessBeanDefinitionRegistry方法
postProcessor.postProcessBeanDefinitionRegistry(registry);这样就会调用MapperScannerConfigurer的postProcessBeanDefinitionRegistry方法：
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {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.registerFilters();scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}这里会开启扫描mapper.xml，ClassPathMapperScanner继承自Spring的ClassPathBeanDefinitionScanner，重写了doScan方法：
public Set<BeanDefinitionHolder> doScan(String... basePackages) {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 {for (BeanDefinitionHolder holder : beanDefinitions) {GenericBeanDefinition 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 MapperFactoryBeandefinition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());definition.setBeanClass(MapperFactoryBean.class);definition.getPropertyValues().add("addToConfig", this.addToConfig);// ......}}return beanDefinitions;}- Set beanDefinitions = super.doScan(basePackages);
调用父类的doScan方法构造每个Mapper的BeanDefinitionHolder，同service一样。
definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
definition.setBeanClass(MapperFactoryBean.class);definition.getPropertyValues().add("addToConfig", this.addToConfig);往definition里设置相关属性，方便后面构造mapper代理类。
第三步：获取指定类型的postProcessorNames（BeanFactoryPostProcessor）并处理
String[] postProcessorNames =beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {if (processedBeans.contains(ppName)) {// skip - already processed in first phase above}else if (isTypeMatch(ppName, PriorityOrdered.class)) {priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));}else if (isTypeMatch(ppName, Ordered.class)) {orderedPostProcessorNames.add(ppName);}else {nonOrderedPostProcessorNames.add(ppName);}
}// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
OrderComparator.sort(priorityOrderedPostProcessors);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);processedBeans集合包含之前两个beanName：
0 = "org.mybatis.spring.mapper.MapperScannerConfigurer#0"
1 = "org.springframework.context.annotation.internalConfigurationAnnotationProcessor"postProcessorNames数组包含三个beanName
0 = "propertyConfigurer"
1 = "org.springframework.context.annotation.internalConfigurationAnnotationProcessor"
2 = "org.mybatis.spring.mapper.MapperScannerConfigurer#0"之前的两个已经创建过了，现在处理剩下的”propertyConfigurer” 一个了。
根据类关系图，自定义的propertyConfigurer刚好也实现了PriorityOrdered接口：
所以将会调用其postProcessBeanFactory方法：
private void invokeBeanFactoryPostProcessors(Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {for (BeanFactoryPostProcessor postProcessor : postProcessors) {postProcessor.postProcessBeanFactory(beanFactory);}
}propertyConfigurer可以是我们自定义的XxPropertyPlaceholderConfigurer，继承自PropertyPlaceholderConfigurer就行了。这里也是一个切入点（关于dataSource的配置等）。
AbstractApplicationContext的registerBeanPostProcessors方法：
第四步：处理BeanPostProcessor相关
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
这里找到7个类：
org.springframework.context.annotation.internalAutowiredAnnotationProcessororg.springframework.context.annotation.internalRequiredAnnotationProcessororg.springframework.context.annotation.internalCommonAnnotationProcessororg.springframework.aop.config.internalAutoProxyCreator&shiroFilterlifecycleBeanPostProcessororg.springframework.context.annotation.ConfigurationClassPostProcessor.importAwareProcessor同处理BeanFactoryPostProcessor一样，也是分为PriorityOrdered、Ordered和其他类型的顺序分别获取bean，然后调用其registerBeanPostProcessors方法注册：
private void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {for (BeanPostProcessor postProcessor : postProcessors) {beanFactory.addBeanPostProcessor(postProcessor);}
}lifecycleBeanPostProcessor在shiroFilter之前初始化。
这里重点看postProcessorNames中name为&shiroFilter。
在AbstractAutowireCapableBeanFactory的applyPropertyValues方法中找到了securityMannger属性，然后又在安全管理器中带出了realm属性，接着又找到adminUserService属性。
第五步：由一个Mapper的初始化引起所有Mapper的创建
这个的重点在于sqlSessionFactory这个属性，中间是根据这个特殊的type去匹配所有的beandefine，adminUserService中有个@autowire注解的adminUserMapper：
if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {MutablePropertyValues newPvs = new MutablePropertyValues(pvs);// Add property values based on autowire by name if applicable.if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {autowireByName(beanName, mbd, bw, newPvs);}// Add property values based on autowire by type if applicable.if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {autowireByType(beanName, mbd, bw, newPvs);}pvs = newPvs;
}看了下AbstractAutowireCapableBeanFactory中的autowireByType方法：
protected void autowireByType(String beanName, AbstractBeanDefinition mbd, BeanWrapper bw, MutablePropertyValues pvs) {TypeConverter converter = getCustomTypeConverter();if (converter == null) {converter = bw;}Set<String> autowiredBeanNames = new LinkedHashSet<String>(4);String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);for (String propertyName : propertyNames) {try {PropertyDescriptor pd = bw.getPropertyDescriptor(propertyName);// Don't try autowiring by type for type Object: never makes sense,// even if it technically is a unsatisfied, non-simple property.if (!Object.class.equals(pd.getPropertyType())) {MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);// Do not allow eager init for type matching in case of a prioritized post-processor.boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());DependencyDescriptor desc = new AutowireByTypeDependencyDescriptor(methodParam, eager);Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);if (autowiredArgument != null) {pvs.add(propertyName, autowiredArgument);}for (String autowiredBeanName : autowiredBeanNames) {registerDependentBean(autowiredBeanName, beanName);if (logger.isDebugEnabled()) {logger.debug("Autowiring by type from bean name '" + beanName + "' via property '" +propertyName + "' to bean named '" + autowiredBeanName + "'");}}autowiredBeanNames.clear();}}catch (BeansException ex) {throw new UnsatisfiedDependencyException(mbd.getResourceDescription(), beanName, propertyName, ex);}}
}- String[] propertyNames = unsatisfiedNonSimpleProperties(mbd, bw);
此方法获取了两个属性：
0 = "sqlSessionFactory"
1 = "sqlSessionTemplate"MapperFactoryBean继承了SqlSessionDaoSupport类：
public abstract class SqlSessionDaoSupport extends DaoSupport {private SqlSession sqlSession;private boolean externalSqlSession;public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {if (!this.externalSqlSession) {this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);}}public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {this.sqlSession = sqlSessionTemplate;this.externalSqlSession = true;}// ......}遍历这两个属性名称，对于sqlSessionFactory：
MethodParameter methodParam = BeanUtils.getWriteMethodParameter(pd);
// Do not allow eager init for type matching in case of a prioritized post-processor.
boolean eager = !PriorityOrdered.class.isAssignableFrom(bw.getWrappedClass());MethodParameter跟SqlSessionDaoSupport中的set方法有关，eager判断也为true，接着：
Object autowiredArgument = resolveDependency(desc, beanName, autowiredBeanNames, converter);
public Object resolveDependency(DependencyDescriptor descriptor, String beanName,Set<String> autowiredBeanNames, TypeConverter typeConverter) throws BeansException {descriptor.initParameterNameDiscovery(getParameterNameDiscoverer());if (descriptor.getDependencyType().equals(ObjectFactory.class)) {return new DependencyObjectFactory(descriptor, beanName);}else if (descriptor.getDependencyType().equals(javaxInjectProviderClass)) {return new DependencyProviderFactory().createDependencyProvider(descriptor, beanName);}else {return doResolveDependency(descriptor, descriptor.getDependencyType(), beanName, autowiredBeanNames, typeConverter);}
}在doResolveDependency方法中：
Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor);DefaultListableBeanFactory的findAutowireCandidates方法：
String[] candidateNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(
this, requiredType, true, descriptor.isEager());
在这个方法中传入的还是adminUserMapper，要求的类型是SqlSessionFactory，还有个参数是DependencyDescriptor。
BeanFactoryUtils的beanNamesForTypeIncludingAncestors方法中：
String[] result = lbf.getBeanNamesForType(type, includeNonSingletons, allowEagerInit);
然后在DefaultListableBeanFactory中getBeanNamesForType：
public String[] getBeanNamesForType(Class<?> type, boolean includeNonSingletons, boolean allowEagerInit) {if (!isConfigurationFrozen() || type == null || !allowEagerInit) {return doGetBeanNamesForType(type, includeNonSingletons, allowEagerInit);}//......
}doGetBeanNamesForType方法中遍历所有beanDefinitionName并判断是否匹配：
boolean matchFound = (allowEagerInit || !isFactoryBean || containsSingleton(beanName)) &&(includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type);isTypeMatch方法中就会针对不同的beanName，与type为SqlSessionFactory做匹配：
if (FactoryBean.class.isAssignableFrom(beanType)) {if (!BeanFactoryUtils.isFactoryDereference(name)) {// If it's a FactoryBean, we want to look at what it creates, not the factory class.beanType = getTypeForFactoryBean(beanName, mbd);if (beanType == null) {return false;}}
}beanType由于是MapperFactoryBean，就会获取相关bean。
getTypeForFactoryBean方法到这里也该终结了：
FactoryBean<?> factoryBean = doGetBean(FACTORY_BEAN_PREFIX + beanName, FactoryBean.class, null, true);这样就开始创建一个个mapper了。
试想一下，就是有没有这样一种可能，当Spring在创建bean的过程中依赖了其他bean，它就会去处理其依赖（创建依赖对象），然后它根据某种情况判断，将所有用到该属性的bean一起都创建了，这样就引起了所有Mapper对象的创建，合乎逻辑。
留下几个问题：
- 其他的属性都是通过配置找到的 mapper是通过注解 如何处理这些差异
- 如何牵一发而动全身 引起200多个mapper的初始化
- 如果没有使用shiro，初始化过程又会是怎么样的 怎么触发 有无规律可循
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