Spring启动过程源码分析(1)

　　　　　　　　　　　——AnnotationConfigApplicationContext之初始化Scanner和Reader

我们以AnnotationConfigApplicationContext为起点来探究Spring的启动过程

首先引入眼帘的就是AnnotationConfigApplicationContext的构造方法，而我们今天只来探讨this();

public AnnotationConfigApplicationContext(Class<?>... componentClasses) {
//this()方法这里就创建了一个Bean工厂和Reader和Scanner
	this();
	register(componentClasses);
	refresh();
}

public AnnotationConfigApplicationContext() {
StartupStep createAnnotatedBeanDefReader = this.getApplicationStartup().start("spring.context.annotated-bean-reader.create");
   // 生成并注册5个BeanDefinition
   // 1.ConfigurationClassPostProcessor
   // 2.AutowiredAnnotationBeanPostProcessor
   // 3.CommonAnnotationBeanPostProcessor
   // 4.EventListenerMethodProcessor
   // 5.DefaultEventListenerFactory
   this.reader = new AnnotatedBeanDefinitionReader(this);
   createAnnotatedBeanDefReader.end();
   // 注册默认的includeFilter
   this.scanner = new ClassPathBeanDefinitionScanner(this);
}

AnnotationConfigApplicationContext首先会生成Reader和Scanner，但在这之前，BeanFactory其实已经实例化完成了

因为AnnotationConfigApplicationContext是GenericApplicationContext的子类，父类的构造器要优先于子类构造器执行，所以在执行AnnotationConfigApplicationContext类的无参构造时，会先执行GenericApplicationContext的无参构造：

public GenericApplicationContext() {
		this.beanFactory = new DefaultListableBeanFactory();
}

一、AnnotatedBeanDefinitionReader

Spring在实例化AnnotatedBeanDefinitionReader做了很多，最主要的就是将内部的后置处理器注册到Spring中

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;
    　　 //ConditionEvaluator对象封装了spring容器的信息
	this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
	/**
	 * 将所有相关的后置处理器注册到这个registry中
	 */
	AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}

　　将spring相关信息记录到conditionEvaluator对象后，spring开始注册相关后置处理器

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(BeanDefinitionRegistry registry, @Nullable Object source) {
	//将刚刚开始第一次new得bean工厂获得，
	DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
	if (beanFactory != null) {
	   //加载组件，其中包括AnnotationAwareOrderComparator和ContextAnnotationAutowireCandidateResolver
	   //AnnotationAwareOrderComparator可以对实现PriorityOrdered、Ordered以及被@Order注解修饰的类进行统一的排序
	   if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
		beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
	    }
           //AutowireCandidateResolver 用来判断一个给定的 bean 是否可以注入，最主要的方法是 isAutowireCandidate
	   if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
		beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
	    }
	}
	//BeanDefinitionHolder中有beanDefinition，beanName,alias
	Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
	if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
	   RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class);
	   def.setSource(source);  //null
	   /**
	    * registerPostProcessor方法：
	    * 将beanName和BeanDefinition按Key—value键值对得方式放在BeanDefinitionMap中
	    * 将BeanName放在BeanDefinitionNames列表中，
	    * 将BeanName和BeanDefinition封装在BeanDefinitionHolder中，
	    * 将封装好得BeanDefinitionHolder放在BeanDefs列表中。
	    * 这里其实就是注册内部的后置处理器
	    */
	   beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
	}
        //AutowiredAnnotationBeanPostProcessor
	if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
	   RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class);
	   def.setSource(source);
	   beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_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);
	   beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
	}
	// Check for JPA support, and if present add the PersistenceAnnotationBeanPostProcessor.
	if (jpaPresent && !registry.containsBeanDefinition(PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME)) {
	   RootBeanDefinition def = new RootBeanDefinition();
	   try {
		def.setBeanClass(ClassUtils.forName(PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME,AnnotationConfigUtils.class.getClassLoader()));
	   }catch (ClassNotFoundException ex) {
		throw new IllegalStateException(
				"Cannot load optional framework class: " + PERSISTENCE_ANNOTATION_PROCESSOR_CLASS_NAME, ex);
	   }
	   def.setSource(source);
	   beanDefs.add(registerPostProcessor(registry, def, PERSISTENCE_ANNOTATION_PROCESSOR_BEAN_NAME));
	}
        //EventListenerMethodProcessor
	if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
	   RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
	   def.setSource(source);
	   beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
	}
        //DefaultEventListenerFactory
	if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
	   RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
	   def.setSource(source);
	   beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
	}
	return beanDefs;
}

二、ClassPathBeanDefinitionScanner

public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry, boolean useDefaultFilters,
										Environment environment, @Nullable ResourceLoader resourceLoader) {

	Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
	this.registry = registry;
	if (useDefaultFilters) {
	//添加includeFilters
	//注册一个@Component注解对应的Filter
		registerDefaultFilters();
	}
	setEnvironment(environment);
	setResourceLoader(resourceLoader);
}

　　在开篇的时候我们提到了Scanner的用法，其中就提及到了includeFilters

DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
ClassPathBeanDefinitionScanner classPathBeanDefinitionScanner = new ClassPathBeanDefinitionScanner(factory);
//得到该包下类的个数
// int scan = classPathBeanDefinitionScanner.scan("com.beans");
// System.out.println(scan);//6
//扫描没有加@Componment注解的类，并注册到容器中，未通过注解或其他方式定义Bean的类也不会添加到容器中
//classPathBeanDefinitionScanner.addExcludeFilter(new AnnotationTypeFilter(Component.class));
//扫描加了@Componment注解的类，并注册到容器中
classPathBeanDefinitionScanner.addIncludeFilter(new AnnotationTypeFilter(Component.class));
//获取bean
Object bean = factory.getBean(BeanTest.class);
System.out.println(bean);//com.beans.BeanTest@5ccddd20

　　Spring会默认向includeFilters添加了@Componment注解

protected void registerDefaultFilters() {
　　this.includeFilters.add(new AnnotationTypeFilter(Component.class));
　　ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
　　try {
　　　　this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
　　　　logger.trace("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning");
　　}catch (ClassNotFoundException ex) {
	// JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.
　　}
　　try {
　　　　this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));
　　　　logger.trace("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");
　　}catch (ClassNotFoundException ex) {
　　　　// JSR-330 API not available - simply skip.
　　}
}

　　到这里Spring就完成了AnnotatedBeanDefinitionReader和ClassPathBeanDefinitionScanner注解的实例化