从Spring源码探究IOC初始化流程

古城微笑少年丶 2023-10-08 16:03 72阅读 0赞

> 随着不断地使用Spring，以及后续的Boot、cloud，不断的体会到这个拯救Java的生态体系的强大，也使我对于这个框架有了极大的好奇心，以至于产生了我为什么不能写一个这样的框架的思考。  
> 通过自学及参考谭勇德(Tom)老师的《Spring 5核心原理于30个类手写实战》这本书，记录此系列博客 。  
> 愿每个想探究Spring原理的人，学习道路一帆风顺

本文是基于**注解**的IOC初始化，不是XML！！！  
代码的含义我都以注释的形式写在代码块中了，请放心查阅

#### 文章目录 ####

*  Annotation 的前世今生
 *  1 定位Bean扫描路径
 *  2 读取Annotation 元数据
 *   *  2.1 AnnotationConfigApplicationContext通过调用注解Bean定义读取器
     *  2.2 AnnotationScopeMetadataResolver解析作用域元数据
     *  2.3 AnnotationConfigUtils处理注解Bean定义类中的通用注解
     *  2.4 AnnotationConfigUtils根据注解 Bean定义类中配置的作用域为其应用相应的代理策略
     *  2.5 BeanDefinitionReaderUtils向容器注册Bean
 *  3 扫描指定包并解析为BeanDefinition
 *   *  3.1 ClassPathBeanDefinitionScanner扫描给定的包及其子包
     *  3.2 ClassPathScanningCandidateComponentProvider扫描给定包及其子包的类
 *  4 注册注解BeanDefinition

## Annotation 的前世今生 ##

从Spring2.0以后的版本中，Spring也引入了基于注解(Annotation)方式的配置，注解(Annotation)是JDK1.5中引入的—个新特性，用于简化Bean的配置，可以取代XML配置文件。  
而开发入员对注解(Annotation)的态度也是萝卜青菜各有所爱，个人认为注解可以大大简化配置，提高开发速度，但也给后期维护增加了难度。目前来说XML方式发展的相对成熟，方便千统—管理。随看SpringBoot的兴起，基于注解的开发甚至实现了零配置。

SpringIOC容器对于**类级别的注解**和**类内部的注解**分以下两种处理策略：

1.  类级别的注解：如@Component,@Repository、@Controller、@Service以及JavaEE6的@ManagedBean和@Named注解都是添加在类上面的类级别注解，Spring容器根据注解的过泡规则扫描读取注解Bean定义类，并将其注册到SpringIOC容器中。
2.  类内部的注解∶如@Autowire、@Value、@Resource以及EJB和WebService相关的注解等，都是添加在类内部的字段或者方法上的类内部注解，SpringlOC容器通过Bean后置注解处理器解析Bean内部的注解。

下面将根据这两种处理策略，分别分析Spring处理注解相关的源码。

## 1 定位Bean扫描路径 ##

在Spring中管理注解Bean定义的容器有两个: AnnotationConfigApplicationContext和AnnotationConfigWebApplicationContex。

这两个类是专门处理Spring 注解方式配置的容器，直接依赖于注解作为容器配置信息来源的IOC容器。

AnnotationConfigWebApplicationContext 是AnnotationConfigApplicationContext 的 Web版本，两者的用法以及对注解的处理方式几乎没有差别。现在我们以AnnotationConfigApplicationContext为例看看它的源码︰

public class AnnotationConfigApplicationContext extends GenericApplicationContext implements AnnotationConfigRegistry {
 
 
 	//保存一个读取注解的Bean定义读取器，并将其设置到容器中
 	private final AnnotatedBeanDefinitionReader reader;
 
 	//保存一个扫描指定类路径中注解Bean定义的扫描器，并将其设置到容器中
 	private final ClassPathBeanDefinitionScanner scanner;
 
 
 	/**
 	 * Create a new AnnotationConfigApplicationContext that needs to be populated
 	 * through {@link #register} calls and then manually {@linkplain #refresh refreshed}.
 	 */
 	//默认构造函数，初始化一个空容器，容器不包含任何 Bean 信息，需要在稍后通过调用其register()
 	//方法注册配置类，并调用refresh()方法刷新容器，触发容器对注解Bean的载入、解析和注册过程
 	public AnnotationConfigApplicationContext() {
 
 		this.reader = new AnnotatedBeanDefinitionReader(this);
 		this.scanner = new ClassPathBeanDefinitionScanner(this);
 	}
 
 	/**
 	 * Create a new AnnotationConfigApplicationContext with the given DefaultListableBeanFactory.
 	 * @param beanFactory the DefaultListableBeanFactory instance to use for this context
 	 */
 	public AnnotationConfigApplicationContext(DefaultListableBeanFactory beanFactory) {
 
 		super(beanFactory);
 		this.reader = new AnnotatedBeanDefinitionReader(this);
 		this.scanner = new ClassPathBeanDefinitionScanner(this);
 	}
 
 	/**
 	 * Create a new AnnotationConfigApplicationContext, deriving bean definitions
 	 * from the given annotated classes and automatically refreshing the context.
 	 * @param annotatedClasses one or more annotated classes,
 	 * e.g. {@link Configuration @Configuration} classes
 	 */
 	//最常用的构造函数，通过将涉及到的配置类传递给该构造函数，以实现将相应配置类中的Bean自动注册到容器中
 	public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {
 
 		this();
 		register(annotatedClasses);
 		refresh();
 	}
 
 	/**
 	 * Create a new AnnotationConfigApplicationContext, scanning for bean definitions
 	 * in the given packages and automatically refreshing the context.
 	 * @param basePackages the packages to check for annotated classes
 	 */
 	//该构造函数会自动扫描以给定的包及其子包下的所有类，并自动识别所有的Spring Bean，将其注册到容器中
 	public AnnotationConfigApplicationContext(String... basePackages) {
 
 		this();
 		//我们自己模拟写过
 		scan(basePackages);
 		refresh();
 	}
 
 
 	/**
 	 * {@inheritDoc}
 	 * Delegates given environment to underlying {@link AnnotatedBeanDefinitionReader}
 	 * and {@link ClassPathBeanDefinitionScanner} members.
 	 */
 	@Override
 	public void setEnvironment(ConfigurableEnvironment environment) {
 
 		super.setEnvironment(environment);
 		this.reader.setEnvironment(environment);
 		this.scanner.setEnvironment(environment);
 	}
 
 	/**
 	 * Provide a custom {@link BeanNameGenerator} for use with {@link AnnotatedBeanDefinitionReader}
 	 * and/or {@link ClassPathBeanDefinitionScanner}, if any.
 	 * Default is {@link org.springframework.context.annotation.AnnotationBeanNameGenerator}.
 	 * Any call to this method must occur prior to calls to {@link #register(Class...)}
 	 * and/or {@link #scan(String...)}.
 	 * @see AnnotatedBeanDefinitionReader#setBeanNameGenerator
 	 * @see ClassPathBeanDefinitionScanner#setBeanNameGenerator
 	 */
 	//为容器的注解Bean读取器和注解Bean扫描器设置Bean名称产生器
 	public void setBeanNameGenerator(BeanNameGenerator beanNameGenerator) {
 
 		this.reader.setBeanNameGenerator(beanNameGenerator);
 		this.scanner.setBeanNameGenerator(beanNameGenerator);
 		getBeanFactory().registerSingleton(
 				AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, beanNameGenerator);
 	}
 
 	/**
 	 * Set the {@link ScopeMetadataResolver} to use for detected bean classes.
 	 * The default is an {@link AnnotationScopeMetadataResolver}.
 	 * Any call to this method must occur prior to calls to {@link #register(Class...)}
 	 * and/or {@link #scan(String...)}.
 	 */
 	//为容器的注解Bean读取器和注解Bean扫描器设置作用范围元信息解析器
 	public void setScopeMetadataResolver(ScopeMetadataResolver scopeMetadataResolver) {
 
 		this.reader.setScopeMetadataResolver(scopeMetadataResolver);
 		this.scanner.setScopeMetadataResolver(scopeMetadataResolver);
 	}
 
 
 	//---------------------------------------------------------------------
 	// Implementation of AnnotationConfigRegistry
 	//---------------------------------------------------------------------
 
 	/**
 	 * Register one or more annotated classes to be processed.
 	 * Note that {@link #refresh()} must be called in order for the context
 	 * to fully process the new classes.
 	 * @param annotatedClasses one or more annotated classes,
 	 * e.g. {@link Configuration @Configuration} classes
 	 * @see #scan(String...)
 	 * @see #refresh()
 	 */
 	//为容器注册一个要被处理的注解Bean，新注册的Bean，必须手动调用容器的
 	//refresh()方法刷新容器，触发容器对新注册的Bean的处理
 	public void register(Class<?>... annotatedClasses) {
 
 		Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
 		this.reader.register(annotatedClasses);
 	}
 
 	/**
 	 * Perform a scan within the specified base packages.
 	 * Note that {@link #refresh()} must be called in order for the context
 	 * to fully process the new classes.
 	 * @param basePackages the packages to check for annotated classes
 	 * @see #register(Class...)
 	 * @see #refresh()
 	 */
 	//扫描指定包路径及其子包下的注解类，为了使新添加的类被处理，必须手动调用
 	//refresh()方法刷新容器
 	public void scan(String... basePackages) {
 
 		Assert.notEmpty(basePackages, "At least one base package must be specified");
 		this.scanner.scan(basePackages);
 	}
 
 
 	//---------------------------------------------------------------------
 	// Convenient methods for registering individual beans
 	//---------------------------------------------------------------------
 
 	/**
 	 * Register a bean from the given bean class, deriving its metadata from
 	 * class-declared annotations, and optionally providing explicit constructor
 	 * arguments for consideration in the autowiring process.
 	 * The bean name will be generated according to annotated component rules.
 	 * @param annotatedClass the class of the bean
 	 * @param constructorArguments argument values to be fed into Spring's
 	 * constructor resolution algorithm, resolving either all arguments or just
 	 * specific ones, with the rest to be resolved through regular autowiring
 	 * (may be {@code null} or empty)
 	 * @since 5.0
 	 */
 	public <T> void registerBean(Class<T> annotatedClass, Object... constructorArguments) {
 
 		registerBean(null, annotatedClass, constructorArguments);
 	}
 
 	/**
 	 * Register a bean from the given bean class, deriving its metadata from
 	 * class-declared annotations, and optionally providing explicit constructor
 	 * arguments for consideration in the autowiring process.
 	 * @param beanName the name of the bean (may be {@code null})
 	 * @param annotatedClass the class of the bean
 	 * @param constructorArguments argument values to be fed into Spring's
 	 * constructor resolution algorithm, resolving either all arguments or just
 	 * specific ones, with the rest to be resolved through regular autowiring
 	 * (may be {@code null} or empty)
 	 * @since 5.0
 	 */
 	public <T> void registerBean(@Nullable String beanName, Class<T> annotatedClass, Object... constructorArguments) {
 
 		this.reader.doRegisterBean(annotatedClass, null, beanName, null,
 				bd -> {
 
 					for (Object arg : constructorArguments) {
 
 						bd.getConstructorArgumentValues().addGenericArgumentValue(arg);
 					}
 				});
 	}
 
 	@Override
 	public <T> void registerBean(@Nullable String beanName, Class<T> beanClass, @Nullable Supplier<T> supplier,
 			BeanDefinitionCustomizer... customizers) {
 
 
 		this.reader.doRegisterBean(beanClass, supplier, beanName, null, customizers);
 	}
 
 }

通过上面的源码分析，我们可以看啊到Spring对注解的处理分为两种方式︰

1.  直接将注解Bean注册到容器中  
    可以在初始化容器时注册;也可以在容器创建之后手动调用注册方法向容器注册，然后通过手动刷新容器，使得容器对注册的注解Bean进行处理。
2.  通过扫描指定的包及其子包下的所有类  
    在初始化注解容器时指定要自动扫描的路径，如果容器创建以后向给定路径动态添加了注解Bean，则需要手动调用容器扫描的方法，然后手动刷新容器，使得容器对所注册的 Bean进行处理。

接下来，将会对两种处理方式详细分析其实现过程。

## 2 读取Annotation 元数据 ##

当创建注解处理容器时，如果传入的初始参数是具体的注解Bean定义类时，注解容器读取并注册。

### 2.1 AnnotationConfigApplicationContext通过调用注解Bean定义读取器 ###

AnnotatedBeanDefinitionReader的register()方法向容器注册指定的注解Bean ,注解Bean定义读取器向容器注册注解Bean的源码如下:

//注册多个注解Bean定义类
 	public void register(Class<?>... annotatedClasses) {
 
 		for (Class<?> annotatedClass : annotatedClasses) {
 
 			registerBean(annotatedClass);
 		}
 	}
 	//注册一个注解Bean定义类
 	public void registerBean(Class<?> annotatedClass) {
 
 		doRegisterBean(annotatedClass, null, null, null);
 	}
 	public <T> void registerBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier) {
 
 		doRegisterBean(annotatedClass, instanceSupplier, null, null);
 	}
 	public <T> void registerBean(Class<T> annotatedClass, String name, @Nullable Supplier<T> instanceSupplier) {
 
 		doRegisterBean(annotatedClass, instanceSupplier, name, null);
 	}
 	//Bean定义读取器注册注解Bean定义的入口方法
 	@SuppressWarnings("unchecked")
 	public void registerBean(Class<?> annotatedClass, Class<? extends Annotation>... qualifiers) {
 
 		doRegisterBean(annotatedClass, null, null, qualifiers);
 	}
 	//Bean定义读取器向容器注册注解Bean定义类
 	@SuppressWarnings("unchecked")
 	public void registerBean(Class<?> annotatedClass, String name, Class<? extends Annotation>... qualifiers) {
 
 		doRegisterBean(annotatedClass, null, name, qualifiers);
 	}
 	//Bean定义读取器向容器注册注解Bean定义类
 	<T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
 			@Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
 
 
 		//根据指定的注解Bean定义类，创建Spring容器中对注解Bean的封装的数据结构
 		AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
 		if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
 
 			return;
 		}
 
 		abd.setInstanceSupplier(instanceSupplier);
 		//========第一步===========================
 
 		//解析注解Bean定义的作用域，若@Scope("prototype")，则Bean为原型类型；
 		//若@Scope("singleton")，则Bean为单态类型
 		ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
 		//为注解Bean定义设置作用域
 		abd.setScope(scopeMetadata.getScopeName());
 		//为注解Bean定义生成Bean名称
 		String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
 
 
 		//========第二步===========================
 		//处理注解Bean定义中的通用注解
 		AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
 		//如果在向容器注册注解Bean定义时，使用了额外的限定符注解，则解析限定符注解。
 		//主要是配置的关于autowiring自动依赖注入装配的限定条件，即@Qualifier注解
 		//Spring自动依赖注入装配默认是按类型装配，如果使用@Qualifier则按名称
 		if (qualifiers != null) {
 
 			for (Class<? extends Annotation> qualifier : qualifiers) {
 
 				//如果配置了@Primary注解，设置该Bean为autowiring自动依赖注入装//配时的首选
 				if (Primary.class == qualifier) {
 
 					abd.setPrimary(true);
 				}
 				//如果配置了@Lazy注解，则设置该Bean为非延迟初始化，如果没有配置，
 				//则该Bean为预实例化
 				else if (Lazy.class == qualifier) {
 
 					abd.setLazyInit(true);
 				}
 				//如果使用了除@Primary和@Lazy以外的其他注解，则为该Bean添加一
 				//个autowiring自动依赖注入装配限定符，该Bean在进autowiring
 				//自动依赖注入装配时，根据名称装配限定符指定的Bean
 				else {
 
 					abd.addQualifier(new AutowireCandidateQualifier(qualifier));
 				}
 			}
 		}
 		for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
 
 			customizer.customize(abd);
 		}
 
 		//创建一个指定Bean名称的Bean定义对象，封装注解Bean定义类数据
 		BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
 		//========第三步===========================
 		//根据注解Bean定义类中配置的作用域，创建相应的代理对象
 		definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
 		//========第四步===========================
 		//向IOC容器注册注解Bean类定义对象
 		BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
 	}

从上面的源码我们可以看出，注册注解Bean定义类的基本步骤︰  
**a、需要使用注解元数据解析器解析注解Bean中关于作用域的配置。**

**b、使用AnnotationConfigUtils的processCommonDefinitionAnnotations()方法处理注解Bean定义类中通用的注解。**

**c、使用AnnotationConfigUtils的applyScopedProxyMode()方法创建对于作用域的代理对象。**

**d、通过BeanDefinitionReaderUtils向容器注册 Bean。**  
我们对上面这四步的源码进行分析：

### 2.2 AnnotationScopeMetadataResolver解析作用域元数据 ###

AnnotationScopeMetadataResolver通过resolveScopeMetadata()方法解析注解Bean定义类的作用域元信息，即判断注册的Bean是原生类型(prototype)还是单态(singleton)类型，其源码如下︰

//解析注解Bean定义类中的作用域元信息
    	@Override
    	public ScopeMetadata resolveScopeMetadata(BeanDefinition definition) {
        
    		ScopeMetadata metadata = new ScopeMetadata();
    		if (definition instanceof AnnotatedBeanDefinition) {
        
    			AnnotatedBeanDefinition annDef = (AnnotatedBeanDefinition) definition;
    			//从注解Bean定义类的属性中查找属性为”Scope”的值，即@Scope注解的值
    			//AnnotationConfigUtils.attributesFor()方法将Bean
    			//中所有的注解和注解的值存放在一个map集合中
    			AnnotationAttributes attributes = AnnotationConfigUtils.attributesFor(
    					annDef.getMetadata(), this.scopeAnnotationType);
    			//将获取到的@Scope注解的值设置到要返回的对象中
    			if (attributes != null) {
        
    				metadata.setScopeName(attributes.getString("value"));
    				//获取@Scope注解中的proxyMode属性值，在创建代理对象时会用到
    				ScopedProxyMode proxyMode = attributes.getEnum("proxyMode");
    				//如果@Scope的proxyMode属性为DEFAULT或者NO
    				if (proxyMode == ScopedProxyMode.DEFAULT) {
        
    					//设置proxyMode为NO
    					proxyMode = this.defaultProxyMode;
    				}
    				//为返回的元数据设置proxyMode
    				metadata.setScopedProxyMode(proxyMode);
    			}
    		}
    		//返回解析的作用域元信息对象
    		return metadata;
    	}

上述代码中的annDef.getMetadata().getAnnotationAttributes()方法就是获取对象中指定类型的注解的值。

### 2.3 AnnotationConfigUtils处理注解Bean定义类中的通用注解 ###

AnnotationConfigUtils类的processCommonDefinitionAnnotations()在向容器注册Bean之前,首先对注解Bean定义类中的通用Spring注解进行处理，源码如下:

//处理Bean定义中通用注解
    	static void processCommonDefinitionAnnotations(AnnotatedBeanDefinition abd, AnnotatedTypeMetadata metadata) {
        
    		AnnotationAttributes lazy = attributesFor(metadata, Lazy.class);
    		//如果Bean定义中有@Lazy注解，则将该Bean预实例化属性设置为@lazy注解的值
    		if (lazy != null) {
        
    			abd.setLazyInit(lazy.getBoolean("value"));
    		}
    
    		else if (abd.getMetadata() != metadata) {
        
    			lazy = attributesFor(abd.getMetadata(), Lazy.class);
    			if (lazy != null) {
        
    				abd.setLazyInit(lazy.getBoolean("value"));
    			}
    		}
    		//如果Bean定义中有@Primary注解，则为该Bean设置为autowiring自动依赖注入装配的首选对象
    		if (metadata.isAnnotated(Primary.class.getName())) {
        
    			abd.setPrimary(true);
    		}
    		//如果Bean定义中有@ DependsOn注解，则为该Bean设置所依赖的Bean名称，
    		//容器将确保在实例化该Bean之前首先实例化所依赖的Bean
    		AnnotationAttributes dependsOn = attributesFor(metadata, DependsOn.class);
    		if (dependsOn != null) {
        
    			abd.setDependsOn(dependsOn.getStringArray("value"));
    		}
    
    		if (abd instanceof AbstractBeanDefinition) {
        
    			AbstractBeanDefinition absBd = (AbstractBeanDefinition) abd;
    			AnnotationAttributes role = attributesFor(metadata, Role.class);
    			if (role != null) {
        
    				absBd.setRole(role.getNumber("value").intValue());
    			}
    			AnnotationAttributes description = attributesFor(metadata, Description.class);
    			if (description != null) {
        
    				absBd.setDescription(description.getString("value"));
    			}
    		}
    	}

### 2.4 AnnotationConfigUtils根据注解 Bean定义类中配置的作用域为其应用相应的代理策略 ###

AnnotationConfigUtils类的applyScopedProxyMode()方法根据注解Bean定义类中配置的作用域@Scope注解的值，为Bean定义应用相应的代理模式，主要是在Spring面向切面编程(AOP)中使用。  
源码如下：

//根据作用域为Bean应用引用的代码模式
    	static BeanDefinitionHolder applyScopedProxyMode(
    			ScopeMetadata metadata, BeanDefinitionHolder definition, BeanDefinitionRegistry registry) {
        
    
    		//获取注解Bean定义类中@Scope注解的proxyMode属性值
    		ScopedProxyMode scopedProxyMode = metadata.getScopedProxyMode();
    		//如果配置的@Scope注解的proxyMode属性值为NO，则不应用代理模式
    		if (scopedProxyMode.equals(ScopedProxyMode.NO)) {
        
    			return definition;
    		}
    		//获取配置的@Scope注解的proxyMode属性值，如果为TARGET_CLASS
    		//则返回true，如果为INTERFACES，则返回false
    		boolean proxyTargetClass = scopedProxyMode.equals(ScopedProxyMode.TARGET_CLASS);
    		//为注册的Bean创建相应模式的代理对象
    		return ScopedProxyCreator.createScopedProxy(definition, registry, proxyTargetClass);
    	}

这段为Bean引用创建相应模式的代理，这里不做深入的分析。

### 2.5 BeanDefinitionReaderUtils向容器注册Bean ###

BeanDefinitionReaderUtils主要是校验BeanDefinition 信息，然后将Bean添加到容器中一个管理BeanDefinition的 HashMap 中。

## 3 扫描指定包并解析为BeanDefinition ##

当创建注解处理容器时，如果传入的初始参数是注解Bean定义类所在的包时，注解容器将扫描给定的包及其子包，将扫描到的注解Bean定义载入并注册。

### 3.1 ClassPathBeanDefinitionScanner扫描给定的包及其子包 ###

AnnotationConfigApplicationContext通过调用类路径Bean定义扫描器ClassPathBeanDefinitionScanner扫描给定包及其子包下的所有类，**主要**源码如下∶

public class ClassPathBeanDefinitionScanner extends ClassPathScanningCandidateComponentProvider {
 
 	//创建一个类路径Bean定义扫描器
 	public ClassPathBeanDefinitionScanner(BeanDefinitionRegistry registry) {
 
 		this(registry, true);
 	}
 	//为容器创建一个类路径Bean定义扫描器，并指定是否使用默认的扫描过滤规则。
 	//即Spring默认扫描配置：@Component、@Repository、@Service、@Controller
 	//注解的Bean，同时也支持JavaEE6的@ManagedBean和JSR-330的@Named注解
 	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");
 		//为容器设置加载Bean定义的注册器
 		this.registry = registry;
 
 		if (useDefaultFilters) {
 
 			registerDefaultFilters();
 		}
 		setEnvironment(environment);
 		//为容器设置资源加载器
 		setResourceLoader(resourceLoader);
 	}
 	//调用类路径Bean定义扫描器入口方法
 	public int scan(String... basePackages) {
 
 		//获取容器中已经注册的Bean个数
 		int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
 
 		//启动扫描器扫描给定包
 		doScan(basePackages);
 
 		// Register annotation config processors, if necessary.
 		//注册注解配置(Annotation config)处理器
 		if (this.includeAnnotationConfig) {
 
 			AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
 		}
 
 		//返回注册的Bean个数
 		return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
 	}
 	//类路径Bean定义扫描器扫描给定包及其子包
 	protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
 
 		Assert.notEmpty(basePackages, "At least one base package must be specified");
 		//创建一个集合，存放扫描到Bean定义的封装类
 		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
 		//遍历扫描所有给定的包
 		for (String basePackage : basePackages) {
 
 			//调用父类ClassPathScanningCandidateComponentProvider的方法
 			//扫描给定类路径，获取符合条件的Bean定义
 			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
 			//遍历扫描到的Bean
 			for (BeanDefinition candidate : candidates) {
 
 				//获取Bean定义类中@Scope注解的值，即获取Bean的作用域
 				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
 				//为Bean设置注解配置的作用域
 				candidate.setScope(scopeMetadata.getScopeName());
 				//为Bean生成名称
 				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
 				//如果扫描到的Bean不是Spring的注解Bean，则为Bean设置默认值，
 				//设置Bean的自动依赖注入装配属性等
 				if (candidate instanceof AbstractBeanDefinition) {
 
 					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
 				}
 				//如果扫描到的Bean是Spring的注解Bean，则处理其通用的Spring注解
 				if (candidate instanceof AnnotatedBeanDefinition) {
 
 					//处理注解Bean中通用的注解，在分析注解Bean定义类读取器时已经分析过
 					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
 				}
 				//根据Bean名称检查指定的Bean是否需要在容器中注册，或者在容器中冲突
 				if (checkCandidate(beanName, candidate)) {
 
 					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
 					//根据注解中配置的作用域，为Bean应用相应的代理模式
 					definitionHolder =
 							AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
 					beanDefinitions.add(definitionHolder);
 					//向容器注册扫描到的Bean
 					registerBeanDefinition(definitionHolder, this.registry);
 				}
 			}
 		}
 		return beanDefinitions;
 	}
 }

类路径Bean定义扫描器ClassPathBeanDefinitionScanner主要通过findCandidateComponents()方法调用其父类ClassPathScanningCandidateComponentProvider类来扫描获取给定包及其子包下的类。

### 3.2 ClassPathScanningCandidateComponentProvider扫描给定包及其子包的类 ###

ClassPathScanningCandidateComponentProvider类的findCandidateComponents()方法具体实现扫描给定类路径包的功能，主要源码如下︰

public class ClassPathScanningCandidateComponentProvider implements EnvironmentCapable, ResourceLoaderAware {
 
 	//保存过滤规则要包含的注解，即Spring默认的@Component、@Repository、@Service、
 	//@Controller注解的Bean，以及JavaEE6的@ManagedBean和JSR-330的@Named注解
 	private final List<TypeFilter> includeFilters = new LinkedList<>();
 	//保存过滤规则要排除的注解
 	private final List<TypeFilter> excludeFilters = new LinkedList<>();
 	//构造方法，该方法在子类ClassPathBeanDefinitionScanner的构造方法中被调用
 	public ClassPathScanningCandidateComponentProvider(boolean useDefaultFilters) {
 
 		this(useDefaultFilters, new StandardEnvironment());
 	}
 	public ClassPathScanningCandidateComponentProvider(boolean useDefaultFilters, Environment environment) {
 
 		//如果使用Spring默认的过滤规则，则向容器注册过滤规则
 		if (useDefaultFilters) {
 
 			registerDefaultFilters();
 		}
 		setEnvironment(environment);
 		setResourceLoader(null);
 	}
 	//向容器注册过滤规则
 	@SuppressWarnings("unchecked")
 	protected void registerDefaultFilters() {
 
 		//向要包含的过滤规则中添加@Component注解类，注意Spring中@Repository
 		//@Service和@Controller都是Component，因为这些注解都添加了@Component注解
 		this.includeFilters.add(new AnnotationTypeFilter(Component.class));
 		//获取当前类的类加载器
 		ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
 		try {
 
 			//向要包含的过滤规则添加JavaEE6的@ManagedBean注解
 			this.includeFilters.add(new AnnotationTypeFilter(
 					((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false));
 			logger.debug("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 {
 
 			//向要包含的过滤规则添加@Named注解
 			this.includeFilters.add(new AnnotationTypeFilter(
 					((Class<? extends Annotation>) 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.
 		}
 	}
 	//扫描给定类路径的包
 	public Set<BeanDefinition> findCandidateComponents(String basePackage) {
 
 		if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
 
 			return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
 		}
 		else {
 
 			return scanCandidateComponents(basePackage);
 		}
 	}
 	private Set<BeanDefinition> addCandidateComponentsFromIndex(CandidateComponentsIndex index, String basePackage) {
 
 		//创建存储扫描到的类的集合
 		Set<BeanDefinition> candidates = new LinkedHashSet<>();
 		try {
 
 			Set<String> types = new HashSet<>();
 			for (TypeFilter filter : this.includeFilters) {
 
 				String stereotype = extractStereotype(filter);
 				if (stereotype == null) {
 
 					throw new IllegalArgumentException("Failed to extract stereotype from "+ filter);
 				}
 				types.addAll(index.getCandidateTypes(basePackage, stereotype));
 			}
 			boolean traceEnabled = logger.isTraceEnabled();
 			boolean debugEnabled = logger.isDebugEnabled();
 			for (String type : types) {
 
 				//为指定资源获取元数据读取器，元信息读取器通过汇编(ASM)读//取资源元信息
 				MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(type);
 				//如果扫描到的类符合容器配置的过滤规则
 				if (isCandidateComponent(metadataReader)) {
 
 					//通过汇编(ASM)读取资源字节码中的Bean定义元信息
 					AnnotatedGenericBeanDefinition sbd = new AnnotatedGenericBeanDefinition(
 							metadataReader.getAnnotationMetadata());
 					if (isCandidateComponent(sbd)) {
 
 						if (debugEnabled) {
 
 							logger.debug("Using candidate component class from index: " + type);
 						}
 						candidates.add(sbd);
 					}
 					else {
 
 						if (debugEnabled) {
 
 							logger.debug("Ignored because not a concrete top-level class: " + type);
 						}
 					}
 				}
 				else {
 
 					if (traceEnabled) {
 
 						logger.trace("Ignored because matching an exclude filter: " + type);
 					}
 				}
 			}
 		}
 		catch (IOException ex) {
 
 			throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
 		}
 		return candidates;
 	}
 	//判断元信息读取器读取的类是否符合容器定义的注解过滤规则
 	protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
 
 		//如果读取的类的注解在排除注解过滤规则中，返回false
 		for (TypeFilter tf : this.excludeFilters) {
 
 			if (tf.match(metadataReader, getMetadataReaderFactory())) {
 
 				return false;
 			}
 		}
 		//如果读取的类的注解在包含的注解的过滤规则中，则返回ture
 		for (TypeFilter tf : this.includeFilters) {
 
 			if (tf.match(metadataReader, getMetadataReaderFactory())) {
 
 				return isConditionMatch(metadataReader);
 			}
 		}
 		//如果读取的类的注解既不在排除规则，也不在包含规则中，则返回false
 		return false;
 	}
 }

## 4 注册注解BeanDefinition ##

AnnotationConfigWebApplicationContext是AnnotationConfigApplicationContext的 Web版，它们对于注解Bean的注册和扫描是基本相同的，但是AnnotationConfigWebApplicationContext对注解Bean定义的载入稍有不同，AnnotationConfigWebApplicationContext注入注解Bean定义：

//载入注解Bean定义资源
 	@Override
 	protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) {
 
 		//为容器设置注解Bean定义读取器
 		AnnotatedBeanDefinitionReader reader = getAnnotatedBeanDefinitionReader(beanFactory);
 		//为容器设置类路径Bean定义扫描器
 		ClassPathBeanDefinitionScanner scanner = getClassPathBeanDefinitionScanner(beanFactory);
 
 		//获取容器的Bean名称生成器
 		BeanNameGenerator beanNameGenerator = getBeanNameGenerator();
 		//为注解Bean定义读取器和类路径扫描器设置Bean名称生成器
 		if (beanNameGenerator != null) {
 
 			reader.setBeanNameGenerator(beanNameGenerator);
 			scanner.setBeanNameGenerator(beanNameGenerator);
 			beanFactory.registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR, beanNameGenerator);
 		}
 
 		//获取容器的作用域元信息解析器
 		ScopeMetadataResolver scopeMetadataResolver = getScopeMetadataResolver();
 		//为注解Bean定义读取器和类路径扫描器设置作用域元信息解析器
 		if (scopeMetadataResolver != null) {
 
 			reader.setScopeMetadataResolver(scopeMetadataResolver);
 			scanner.setScopeMetadataResolver(scopeMetadataResolver);
 		}
 
 		if (!this.annotatedClasses.isEmpty()) {
 
 			if (logger.isInfoEnabled()) {
 
 				logger.info("Registering annotated classes: [" +
 						StringUtils.collectionToCommaDelimitedString(this.annotatedClasses) + "]");
 			}
 			reader.register(this.annotatedClasses.toArray(new Class<?>[this.annotatedClasses.size()]));
 		}
 
 		if (!this.basePackages.isEmpty()) {
 
 			if (logger.isInfoEnabled()) {
 
 				logger.info("Scanning base packages: [" +
 						StringUtils.collectionToCommaDelimitedString(this.basePackages) + "]");
 			}
 			scanner.scan(this.basePackages.toArray(new String[this.basePackages.size()]));
 		}
 
 		//获取容器定义的Bean定义资源路径
 		String[] configLocations = getConfigLocations();
 		//如果定位的Bean定义资源路径不为空
 		if (configLocations != null) {
 
 			for (String configLocation : configLocations) {
 
 				try {
 
 					//使用当前容器的类加载器加载定位路径的字节码类文件
 					Class<?> clazz = ClassUtils.forName(configLocation, getClassLoader());
 					if (logger.isInfoEnabled()) {
 
 						logger.info("Successfully resolved class for [" + configLocation + "]");
 					}
 					reader.register(clazz);
 				}
 				catch (ClassNotFoundException ex) {
 
 					if (logger.isDebugEnabled()) {
 
 						logger.debug("Could not load class for config location [" + configLocation +
 								"] - trying package scan. " + ex);
 					}
 					//如果容器类加载器加载定义路径的Bean定义资源失败
 					//则启用容器类路径扫描器扫描给定路径包及其子包中的类
 					int count = scanner.scan(configLocation);
 					if (logger.isInfoEnabled()) {
 
 						if (count == 0) {
 
 							logger.info("No annotated classes found for specified class/package [" + configLocation + "]");
 						}
 						else {
 
 							logger.info("Found " + count + " annotated classes in package [" + configLocation + "]");
 						}
 					}
 				}
 			}
 		}
 	}

以上就是解析和注入注解配置资源的全过程分析。  
至此，结束