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牛旦教育IT课堂 2019-03-05 15:25:54

原文： http://www.jianshu.com/p/573bdae020e9

Spring 基于注解启动

主要有两个Class实现注解启动

• AnnotationConfigApplicationContext
• AnnotationConfigWebApplicationContext

我们以AnnotationConfigApplicationContext 为研究对象

AnnotationConfigApplicationContext.png

引入Spring 最小依赖

    
    
     org.springframework
     
    
     spring-context
     
    
     ${spring.version}
     
   

编写器启动代码

public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(); applicationContext.register(BeanConfig.class); applicationContext.refresh(); Date date = applicationContext.getBean("date",Date.class); System.out.println(date); }

AnnotationConfigApplicationContext 构造函数

public AnnotationConfigApplicationContext() { //负责注册Class ，读取器 this.reader = new AnnotatedBeanDefinitionReader(this); //负责扫描指定类路径下的Class，注册bean this.scanner = new ClassPathBeanDefinitionScanner(this); }

AnnotatedBeanDefinitionReader 构造方法

public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) { this(registry, getOrCreateEnvironment(registry)); } public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) { Assert.notNull(registry, "BeanDefinitionRegistry must not be null"); Assert.notNull(environment, "Environment must not be null"); this.registry = registry; //初始化ConditionEvaluator this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);  /** 在給定的注册表中註冊所有相关的post processors * 判断容器是否已经存在给定注册表的bean，如果没有注册bean，并将bean放入容器中 * 把所有的处理处理器列出来 * ConfigurationClassPostProcessor 內部管理的配置注解处理器 * AutowiredAnnotationBeanPostProcessor 内部管理@Autowired 的处理器 * RequiredAnnotationBeanPostProcessor @Required的处理器 * CommonAnnotationBeanPostProcessor JSR-250注解处理器 ，先判断是否支持jsr，如果支持注册 * PersistenceAnnotationBeanPostProcessor JPA管理 先使用类加载器查找是否存在，如果有这个包则注册 * EventListenerMethodProcessor @EventListener的处理器 * DefaultEventListenerFactory 管理EventListenerFactory处理器 */ AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry); }

ConditionEvaluator这个对象干什么,点击进去

public ConditionEvaluator(@Nullable BeanDefinitionRegistry registry, @Nullable Environment environment, @Nullable ResourceLoader resourceLoader) { this.context = new ConditionContextImpl(registry, environment, resourceLoader);  } //ConditionContextImpl 实现了ConditionContext接口，ConditionEvaluator静态内部类 public ConditionContextImpl(@Nullable BeanDefinitionRegistry registry, @Nullable Environment environment, @Nullable ResourceLoader resourceLoader) { this.registry = registry; this.beanFactory = deduceBeanFactory(registry); this.environment = (environment != null ? environment : deduceEnvironment(registry)); this.resourceLoader = (resourceLoader != null ? resourceLoader : deduceResourceLoader(registry)); this.classLoader = deduceClassLoader(resourceLoader, this.beanFactory); }

可以知道 ConditionEvaluator 使用外部传参的方法初始化了Spring容器顶级对象

BeanFactory , Environment , ResourceLoader , ClassLoader 。再将这些传给ConditionContextImpl为接下来的解析 @Conditional 注解做好准备

ClassPathBeanDefinitionScanner构造函数

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) { this(registry, true); } public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters) { this(registry, useDefaultFilters, getOrCreateEnvironment(registry)); } public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters, Environment environment) { this(registry, useDefaultFilters, environment, (registry instanceof ResourceLoader ? (ResourceLoader) registry : null)); } public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters, Environment environment, @Nullable ResourceLoader resourceLoader) { Assert.notNull(registry, "BeanDefinitionRegistry must not be null"); this.registry = registry; if (useDefaultFilters) { registerDefaultFilters(); } setEnvironment(environment); setResourceLoader(resourceLoader); } protected void registerDefaultFilters() { this.includeFilters.add(new AnnotationTypeFilter(Component.class)); ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader(); try { this.includeFilters.add(new AnnotationTypeFilter( ((Class
   ) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false)); logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning"); } catch (ClassNotFoundException ex) { } try { this.includeFilters.add(new AnnotationTypeFilter( ((Class
   ) ClassUtils.forName("javax.inject.Named", cl)), false)); logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning"); } catch (ClassNotFoundException ex) { // JSR-330 API not available - simply skip. } }

绕了地球几圈了，其实就是将Spring 顶级接口 Environment , ResourceLoader 赋值，使用默认注解过滤器，首先将@Component加入List中，判断当前环境是否支持 JSR-250 ， JSR-330 ，相应加入过滤器中。也就是这个扫描器默认只扫描 @Component 或者 JSR-250 ， JSR-330 的标记的Class。

applicationContext.register(BeanConfig.class)

public void register(Class
   ... annotatedClasses) { Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified"); this.reader.register(annotatedClasses); //调用 刚刚初始化读取器 } |============================AnnotatedBeanDefinitionReader 读取器代码====================================================================================================== public void register(Class
   ... annotatedClasses) { for (Class
    annotatedClass : annotatedClasses) { registerBean(annotatedClass); } } public void registerBean(Class
    annotatedClass) { doRegisterBean(annotatedClass, null, null, null); }  /** *从给定的bean解析Class给定的注解，执行相应的初始化，保存到Spring容器中 */ 
   
     void doRegisterBean(Class
    
      annotatedClass, @Nullable Supplier
     
       instanceSupplier, @Nullable String name, @Nullable Class
      [] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) { //根据Class的Annotated 得出元数据 AnnotationMetadata AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass); /** * 判断注册的Class 是否包含@Conditional注解，如果有获取全部value，放入List中 * 排序后，遍历所有的Conditiion的实现，使用反射获取对象，执行matches方法， * 如果发现有返回false，中断循环直接返回true， */ if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) { //如果 @Conditional条件不满足，不进行注册 return; } abd.setInstanceSupplier(instanceSupplier); //解析Class是否有@Scope,解析@Scope注解返回ScopeMetadata对象，没有直接返回空 ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd); abd.setScope(scopeMetadata.getScopeName()); //判断注解上Value是否有值，有就使用这个作为BeanName，没有则取类名  String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry)); //继续解析AnnotationMetadata的@Lazy,@Primary，@DependsOn，@Role，@Description的注解，放入结果放入对象的属性中 AnnotationConfigUtils.processCommonDefinitionAnnotations(abd); //这个类只是BeanDefinition 包装类 BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName); //是否需要代理类，如果是则修改内部属性，重新生成BeanDefinition 对象 definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry); //调用DefaultListableBeanFactory.registerBeanDefinition的方法，做一些安全性校验再，将definitionHolder 放入register容器中 BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry); }
     
    
   

这个方法就是将注册的Bean，解析Class上的注解，初始化注解数据，做相应处理，转化成BeanDefinition ,放入Spring 容器中保存起来。

我们看下 BeanDefinition 是怎么实现注册到Spring的容器中，主要由 DefaultListableBeanFactory.registerBeanDefinition 来实现

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException { Assert.hasText(beanName, "Bean name must not be empty"); Assert.notNull(beanDefinition, "BeanDefinition must not be null"); if (beanDefinition instanceof AbstractBeanDefinition) { try { //对beanDefinition 进行校验判断MethodOverrides不能为空，必须拥有工厂方法 ((AbstractBeanDefinition) beanDefinition).validate(); } catch (BeanDefinitionValidationException ex) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex); } } BeanDefinition oldBeanDefinition; oldBeanDefinition = this.beanDefinitionMap.get(beanName);  if (oldBeanDefinition != null) { //这个方法是判断是否允许出现重名bean，并且是不同的定义bean，是否可以覆盖前者 if (!isAllowBeanDefinitionOverriding()) { throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound."); } else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) { // e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE if (this.logger.isWarnEnabled()) { this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else if (!beanDefinition.equals(oldBeanDefinition)) { if (this.logger.isInfoEnabled()) { this.logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } else { if (this.logger.isDebugEnabled()) { this.logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]"); } } this.beanDefinitionMap.put(beanName, beanDefinition); } else { //调用alreadyCreated.isEmpty()，alreadyCreated Set对象，保存已经创建beanName //文档中表示created，跟这里注册应该不是同一个行为，这个要看到后面才知道什么意思 if (hasBeanCreationStarted()) { synchronized (this.beanDefinitionMap) {//更新数据 this.beanDefinitionMap.put(beanName, beanDefinition); List
   
     updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1); updatedDefinitions.addAll(this.beanDefinitionNames); updatedDefinitions.add(beanName); this.beanDefinitionNames = updatedDefinitions; if (this.manualSingletonNames.contains(beanName)) { Set
    
      updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames); updatedSingletons.remove(beanName); this.manualSingletonNames = updatedSingletons; } } } else {  //Spring beanDefinition 容器，一个Map转载 this.beanDefinitionMap.put(beanName, beanDefinition); //保存beanName，主要用于记录每个bean注册顺序 this.beanDefinitionNames.add(beanName); //删除单例，注册成一个普通bean this.manualSingletonNames.remove(beanName); } this.frozenBeanDefinitionNames = null; } if (oldBeanDefinition != null || containsSingleton(beanName)) {  //更新Spring容器里beanName resetBeanDefinition(beanName); } }
    
   

将beanDefinition注册到Spring容器中，并没有太多复杂的逻辑，只是做一些安全性的检查。

BeanDefinition

一个BeanDefinition描述了一个bean的实例，包括属性值，构造方法参数值和继承自它的类的更多信息。BeanDefinition仅仅是一个最简单的接口，主要功能是允许BeanFactoryPostProcessor 例如PropertyPlaceHolderConfigure 能够检索并修改属性值和别的bean的元数据（译注）

Spring 容器 beanDefinition 主要分为 RootBeanDefinition , AnnotatedGenericBeanDefinition 这两种

• RootBeanDefinition Spring Factory中的特定bean
• AnnotatedGenericBeanDefinition 用户自定义bean

Spring 启动流程总结

AnnotationConfigApplicationContext 初始化.png

这些BeanDefinition只是放入到Spirng 容器中，并没有进行任何初始化对象的操作，真正的IOC操作都在 refresh() ,这个方法有空再进行分析。