[心得体会]Spring容器的初始化

1. Spring容器的初始化过程

public AnnotationConfigApplicationContext(Class<?>... annotatedClasses) {   
    this();   
    register(annotatedClasses);   
    refresh();
}

1. this() 方法的执行过程

(1) 父类构造方法的初始化

1) 在DefaultResourceLoader 类里面初始化创建了个classLoad2) PathMatchingResourcePatternResolver

① 初始化了resourceLoader 属性

② 同时创建了

private PathMatcher pathMatcher = new AntPathMatcher(); 

3) GenericApplicationContext类初始化this.beanFactory

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

跟进DefaultListableBeanFactory这个方法

public DefaultListableBeanFactory() {   super();}

public AbstractAutowireCapableBeanFactory() {
        super();
        ignoreDependencyInterface(BeanNameAware.class);
        ignoreDependencyInterface(BeanFactoryAware.class);
        ignoreDependencyInterface(BeanClassLoaderAware.class);
    }

上面这个代码主要的功能就是初始化很多属性, 比如Map之类的属性并且忽略了三个Aware

(2) 方法AnnotatedBeanDefinitionReader(this)的执行

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;
        this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
        AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    }

public static void registerAnnotationConfigProcessors(BeanDefinitionRegistry registry) {
    registerAnnotationConfigProcessors(registry, null);
}

进入上面的方法之后一顿操作就做了两件事情

DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
        if (beanFactory != null) {
            if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
                beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
            }
            if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
                beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
            }
        }

初始化了两个对象

DependencyComparator

AutowireCandidateResolver

注册了几个处理器

org.springframework.context.annotation.internalConfigurationAnnotationProcessor

org.springframework.context.annotation.internalAutowiredAnnotationProcessor

org.springframework.context.annotation.internalCommonAnnotationProcessor

org.springframework.context.annotation.internalPersistenceAnnotationProcessor

org.springframework.context.event.internalEventListenerProcessor

org.springframework.context.event.internalEventListenerFactory

(3) 方法ClassPathBeanDefinitionScanner(this)的执行

    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) {
            // 默认的过滤器
            registerDefaultFilters();
        }
        setEnvironment(environment);
        setResourceLoader(resourceLoader);
    }

注入默认的类型过滤器

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.
        }
    }

2. 配置类的扫描和注册

(1) register(annotatedClasses)注册方式

private final AnnotatedBeanDefinitionReader reader; // bean读取加载器

    public void register(Class<?>... annotatedClasses) {
        Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
        this.reader.register(annotatedClasses);
    }

<T> void doRegisterBean(Class<T> annotatedClass, @Nullable Supplier<T> instanceSupplier, @Nullable String name,
            @Nullable Class<? extends Annotation>[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {

    // 作用: 将Class类保存到abd对象里面, 并且保存了这个配置类中的所以注解
        AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
        // 判断是否存在condition注解, 是否可以跳过
        if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
            return;
        }
        
        abd.setInstanceSupplier(instanceSupplier);
        // 解析scope注解
        ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
        // 设置这个注解的value
        abd.setScope(scopeMetadata.getScopeName());
        // 获取beanName名字
        String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
        // 判断是否有: lazy Primary dependsOn role description 这些注解
        AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
        if (qualifiers != null) {
            for (Class<? extends Annotation> qualifier : qualifiers) {
                if (Primary.class == qualifier) {
                    abd.setPrimary(true);
                }
                else if (Lazy.class == qualifier) {
                    abd.setLazyInit(true);
                }
                else {
                    abd.addQualifier(new AutowireCandidateQualifier(qualifier));
                }
            }
        }
        for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
            customizer.customize(abd);
        }
        // 创建BeanDefinitionHolder
        BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
        // 创建代理类
        definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
        // 注册beandefinition
        BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
    }

(2) 使用scan(basePackages)实现的注册

public int scan(String... basePackages) {
    int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
    // 扫描包
    doScan(basePackages);

    // 这里就是this()方法里面执行的注册的6个类, 不过现在默认不会再初始化了
    if (this.includeAnnotationConfig) {
        AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    }
    
    return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
}

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Assert.notEmpty(basePackages, "At least one base package must be specified");
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
    // 这个就是我们 AnnotationConfigApplicationContext ac = new AnnotationConfigApplicationContext("com"); 定义的扫描包的位置, 里面基本上都是配置类
    for (String basePackage : basePackages) {
        // 扫描出所有我们定义的bean
        Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
        for (BeanDefinition candidate : candidates) {
            // scope 的读取和设置
            ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
            candidate.setScope(scopeMetadata.getScopeName());
            // 生成BeanName的名字
            String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
            if (candidate instanceof AbstractBeanDefinition) {
                // 初始化后置处理器
                postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
            }
            if (candidate instanceof AnnotatedBeanDefinition) {
                // 判断是否有 lazy dependsOn role description 属性
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
            }
            if (checkCandidate(beanName, candidate)) {
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                definitionHolder =
                        AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                // 把BeanDefinition设置到备份的这个对象中, 到时候返回
                beanDefinitions.add(definitionHolder);
                // 注册BeanDefinition
                registerBeanDefinition(definitionHolder, this.registry);
            }
        }
    }
    return beanDefinitions;
}

public Set<BeanDefinition> findCandidateComponents(String basePackage) {
    if (this.componentsIndex != null && indexSupportsIncludeFilters()) {
        return addCandidateComponentsFromIndex(this.componentsIndex, basePackage);
    }
    else {
        return scanCandidateComponents(basePackage);
    }
}

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
    Set<BeanDefinition> candidates = new LinkedHashSet<>();
    try {
        String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
                resolveBasePackage(basePackage) + '/' + this.resourcePattern;
        // 获取所有的字节码文件
        Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
        boolean traceEnabled = logger.isTraceEnabled();
        boolean debugEnabled = logger.isDebugEnabled();
        for (Resource resource : resources) {
            if (traceEnabled) {
                logger.trace("Scanning " + resource);
            }
            if (resource.isReadable()) {
                try {
                    MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
                    if (isCandidateComponent(metadataReader)) {
                        ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                        sbd.setResource(resource);
                        sbd.setSource(resource);
                        if (isCandidateComponent(sbd)) {
                            if (debugEnabled) {
                                logger.debug("Identified candidate component class: " + resource);
                            }
                            candidates.add(sbd);
                        }
                        else {
                            if (debugEnabled) {
                                logger.debug("Ignored because not a concrete top-level class: " + resource);
                            }
                        }
                    }
                    else {
                        if (traceEnabled) {
                            logger.trace("Ignored because not matching any filter: " + resource);
                        }
                    }
                }
                catch (Throwable ex) {
                    throw new BeanDefinitionStoreException(
                            "Failed to read candidate component class: " + resource, ex);
                }
            }
            else {
                if (traceEnabled) {
                    logger.trace("Ignored because not readable: " + resource);
                }
            }
        }
    }
    catch (IOException ex) {
        throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
    }
    return candidates;
}

@Override
public Resource[] getResources(String locationPattern) throws IOException {
    Assert.notNull(locationPattern, "Location pattern must not be null");
    if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
        // a class path resource (multiple resources for same name possible)
        if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
            // a class path resource pattern
            return findPathMatchingResources(locationPattern);
        }
        else {
            // all class path resources with the given name
            return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
        }
    }
    else {
        // Generally only look for a pattern after a prefix here,
        // and on Tomcat only after the "*/" separator for its "war:" protocol.
        int prefixEnd = (locationPattern.startsWith("war:") ? locationPattern.indexOf("*/") + 1 :
                locationPattern.indexOf(':') + 1);
        if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
            // a file pattern
            return findPathMatchingResources(locationPattern);
        }
        else {
            // a single resource with the given name
            return new Resource[] {getResourceLoader().getResource(locationPattern)};
        }
    }
}

protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
    String rootDirPath = determineRootDir(locationPattern);
    String subPattern = locationPattern.substring(rootDirPath.length());
    // 获取包目录
    Resource[] rootDirResources = getResources(rootDirPath);
    Set<Resource> result = new LinkedHashSet<>(16);
    // 遍历包, com.zhazha.dao, com.zhazha.service, com.zhazha.controller
    for (Resource rootDirResource : rootDirResources) {
        rootDirResource = resolveRootDirResource(rootDirResource);
        URL rootDirUrl = rootDirResource.getURL();
        if (equinoxResolveMethod != null && rootDirUrl.getProtocol().startsWith("bundle")) {
            URL resolvedUrl = (URL) ReflectionUtils.invokeMethod(equinoxResolveMethod, null, rootDirUrl);
            if (resolvedUrl != null) {
                rootDirUrl = resolvedUrl;
            }
            rootDirResource = new UrlResource(rootDirUrl);
        }
        if (rootDirUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
            result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirUrl, subPattern, getPathMatcher()));
        }
        else if (ResourceUtils.isJarURL(rootDirUrl) || isJarResource(rootDirResource)) {
            result.addAll(doFindPathMatchingJarResources(rootDirResource, rootDirUrl, subPattern));
        }
        else {
            // 遍历出一个包, 放入这个方法进行扫描字节码文件
            result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
        }
    }
    if (logger.isTraceEnabled()) {
        logger.trace("Resolved location pattern [" + locationPattern + "] to resources " + result);
    }
    return result.toArray(new Resource[0]);
}

protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource, String subPattern)
            throws IOException {

    File rootDir;
    try {
        rootDir = rootDirResource.getFile().getAbsoluteFile();
    }
    catch (FileNotFoundException ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Cannot search for matching files underneath " + rootDirResource +
                    " in the file system: " + ex.getMessage());
        }
        return Collections.emptySet();
    }
    catch (Exception ex) {
        if (logger.isInfoEnabled()) {
            logger.info("Failed to resolve " + rootDirResource + " in the file system: " + ex);
        }
        return Collections.emptySet();
    }
    // 遍历com.zhazha.dao这个包里面的.class字节码文件
    return doFindMatchingFileSystemResources(rootDir, subPattern);
}

protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {
    if (logger.isTraceEnabled()) {
        logger.trace("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");
    }
    // 获得.class字节码文件的列表
    Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern);
    Set<Resource> result = new LinkedHashSet<>(matchingFiles.size());
    // 把发现的所有.class文件的file对象放入result中, 这个result是资源的
    for (File file : matchingFiles) {
        result.add(new FileSystemResource(file));
    }
    return result;
}

protected Set<File> retrieveMatchingFiles(File rootDir, String pattern) throws IOException {
    if (!rootDir.exists()) {
        // Silently skip non-existing directories.
        if (logger.isDebugEnabled()) {
            logger.debug("Skipping [" + rootDir.getAbsolutePath() + "] because it does not exist");
        }
        return Collections.emptySet();
    }
    if (!rootDir.isDirectory()) {
        // Complain louder if it exists but is no directory.
        if (logger.isInfoEnabled()) {
            logger.info("Skipping [" + rootDir.getAbsolutePath() + "] because it does not denote a directory");
        }
        return Collections.emptySet();
    }
    if (!rootDir.canRead()) {
        if (logger.isInfoEnabled()) {
            logger.info("Skipping search for matching files underneath directory [" + rootDir.getAbsolutePath() +
                    "] because the application is not allowed to read the directory");
        }
        return Collections.emptySet();
    }
    String fullPattern = StringUtils.replace(rootDir.getAbsolutePath(), File.separator, "/");
    if (!pattern.startsWith("/")) {
        fullPattern += "/";
    }
    fullPattern = fullPattern + StringUtils.replace(pattern, File.separator, "/");
    Set<File> result = new LinkedHashSet<>(8);
    // 匹配字节码文件.class, 将结果放入result
    doRetrieveMatchingFiles(fullPattern, rootDir, result);
    return result;
}

protected void doRetrieveMatchingFiles(String fullPattern, File dir, Set<File> result) throws IOException {
    if (logger.isTraceEnabled()) {
        logger.trace("Searching directory [" + dir.getAbsolutePath() +
                "] for files matching pattern [" + fullPattern + "]");
    }
    // 获取包下面的所有文件, 不断的遍历直到找到.class
    for (File content : listDirectory(dir)) {
        String currPath = StringUtils.replace(content.getAbsolutePath(), File.separator, "/");
        if (content.isDirectory() && getPathMatcher().matchStart(fullPattern, currPath + "/")) {
            // 不可读的话
            if (!content.canRead()) {
                if (logger.isDebugEnabled()) {
                    logger.debug("Skipping subdirectory [" + dir.getAbsolutePath() +
                            "] because the application is not allowed to read the directory");
                }
            }
            else {
                // 回调方法
                doRetrieveMatchingFiles(fullPattern, content, result);
            }
        }
        // 把找到的.class字节码放入结果中
        if (getPathMatcher().match(fullPattern, currPath)) {
            result.add(content);
        }
    }
}

3. refresh方法详情

总共分为13个步骤

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// 准备此上下文以进行刷新。
			prepareRefresh();

			// 告诉子类刷新内部bean工厂。
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// 准备在这种情况下使用的bean工厂。
			prepareBeanFactory(beanFactory);

			try {
				// 允许在上下文子类中对bean工厂进行后处理。(但是里面的方法是空的)
				postProcessBeanFactory(beanFactory);

				// 调用在上下文中注册为bean的工厂处理器。
				invokeBeanFactoryPostProcessors(beanFactory);

				// 注册拦截Bean创建的Bean处理器。
				registerBeanPostProcessors(beanFactory);

				// 为此上下文初始化消息源。
				initMessageSource();

				// 为此上下文初始化事件多播器。
				initApplicationEventMulticaster();

				// 在特定上下文子类中初始化其他特殊bean。
				onRefresh();

				// 检查侦听器bean并注册它们。
				registerListeners();

				// 实例化所有剩余的（非延迟初始化）单例。
				finishBeanFactoryInitialization(beanFactory);

				// 最后一步：发布相应的事件。
				finishRefresh();
			}

			catch (BeansException ex) {
				if (logger.isWarnEnabled()) {
					logger.warn("Exception encountered during context initialization - " +
							"cancelling refresh attempt: " + ex);
				}

				// 销毁已创建的单例以避免资源悬空。
				destroyBeans();

				// 重置“活动”标志。
				cancelRefresh(ex);

				// 将异常传播给呼叫者。
				throw ex;
			}

			finally {
				// 在Spring的核心中重置常见的自省缓存，因为我们可能再也不需要单例bean的元数据了。
				resetCommonCaches();
			}
		}
	}

(1) 准备此上下文以进行刷新

protected void prepareRefresh() {
		// 获取spring容器开启时间
		this.startupDate = System.currentTimeMillis();
    	// 标记closed属性为false
		this.closed.set(false);
		// 激活标志为true
		this.active.set(true);

		if (logger.isDebugEnabled()) {
			if (logger.isTraceEnabled()) {
				logger.trace("Refreshing " + this);
			}
			else {
				logger.debug("Refreshing " + getDisplayName());
			}
		}

		// 在上下文环境中初始化任何占位符属性源
		initPropertySources();

		// 验证所有标记为必需的属性都是可解析的:
		// see ConfigurablePropertyResolver#setRequiredProperties
		getEnvironment().validateRequiredProperties();

		// 存储预刷新应用程序 / 监听器..。
		if (this.earlyApplicationListeners == null) {
			this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);
		}
		else {
			// 将本地应用程序侦听器重置为预刷新状态。
			this.applicationListeners.clear();
			this.applicationListeners.addAll(this.earlyApplicationListeners);
		}

		// 允许收集早期应用程序事件，以便在多管道可用时发布..。
		this.earlyApplicationEvents = new LinkedHashSet<>();
	}

添加监听器

(2) 告诉子类刷新内部bean工厂

	protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
        // 产生id
		refreshBeanFactory();
		return getBeanFactory();
	}

里面就这一句话
this.beanFactory.setSerializationId(getId());

(3) 准备在这种情况下使用的bean工厂

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    // 告诉内部 bean 工厂使用上下文的类装入器等
    beanFactory.setBeanClassLoader(getClassLoader());
    beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
    beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

    // 使用上下文回调配置 bean 工厂
    beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
    beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
    beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
    beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
    beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
    beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

    // 在普通工厂中，BeanFactory 接口未注册为可解析类型。
    // Messagesource 以 bean 的形式注册(并在自动装配中找到)。
    beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
    beanFactory.registerResolvableDependency(ResourceLoader.class, this);
    beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
    beanFactory.registerResolvableDependency(ApplicationContext.class, this);

    // 将检测内部 bean 的早期后处理程序注册为 ApplicationListeners。
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));

    // 检测 LoadTimeWeaver 并准备编织(如果发现)。
    if (beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        // 设置用于类型匹配的临时 ClassLoader。
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }

    // 注册默认环境 bean。
    if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {
        beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());
    }
    if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {
        beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());
    }
    if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {
        beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());
    }
}

(4) 允许在上下文子类中对bean工厂进行后处理。(但是里面的方法是空的)

内部方法为空

(5) 调用在上下文中注册为bean的工厂后置处理器

invokeBeanFactoryPostProcessors(beanFactory);

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 传入beanFactory和所有的PostProcessors, 进行PostProcessors的注册
    PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

    // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
    // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
    if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
        beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
        beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    }
}

把注解放入List<BeanDefinitionHolder> configCandidates = new ArrayList<>();

// 配置类的解析读取器: 解析ComponeScan注解扫描的所有bean
ConfigurationClassParser parser = new ConfigurationClassParser(
				this.metadataReaderFactory, this.problemReporter, this.environment,
				this.resourceLoader, this.componentScanBeanNameGenerator, registry);

// 这里开始真正的解析
parser.parse(candidates);

最终解析完毕之后会把对象放入parser的configurationClasses属性之中

public void parse(Set<BeanDefinitionHolder> configCandidates) {
    for (BeanDefinitionHolder holder : configCandidates) {
        BeanDefinition bd = holder.getBeanDefinition();
        try {
            if (bd instanceof AnnotatedBeanDefinition) {
                // 我们的这个案例最终往这里走
                parse(((AnnotatedBeanDefinition) bd).getMetadata(), holder.getBeanName());
            }
            else if (bd instanceof AbstractBeanDefinition && ((AbstractBeanDefinition) bd).hasBeanClass()) {
                parse(((AbstractBeanDefinition) bd).getBeanClass(), holder.getBeanName());
            }
            else {
                parse(bd.getBeanClassName(), holder.getBeanName());
            }
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
        catch (Throwable ex) {
            throw new BeanDefinitionStoreException(
                    "Failed to parse configuration class [" + bd.getBeanClassName() + "]", ex);
        }
    }

    this.deferredImportSelectorHandler.process();
}

protected void processConfigurationClass(ConfigurationClass configClass) throws IOException {
    // 检测条件判断
    if (this.conditionEvaluator.shouldSkip(configClass.getMetadata(), ConfigurationPhase.PARSE_CONFIGURATION)) {
        return;
    }
	// 判断容器是否已经存在这个配置类
    ConfigurationClass existingClass = this.configurationClasses.get(configClass);
    if (existingClass != null) {
        if (configClass.isImported()) {
            if (existingClass.isImported()) {
                // 合并
                existingClass.mergeImportedBy(configClass);
            }
            // Otherwise ignore new imported config class; existing non-imported class overrides it.
            return;
        }
        else {
            // Explicit bean definition found, probably replacing an import.
            // Let's remove the old one and go with the new one.
            this.configurationClasses.remove(configClass);
            this.knownSuperclasses.values().removeIf(configClass::equals);
        }
    }

    // 递归地处理配置类及其超类层次结构.
    SourceClass sourceClass = asSourceClass(configClass);
    do {
        sourceClass = doProcessConfigurationClass(configClass, sourceClass);
    }
    while (sourceClass != null);

    this.configurationClasses.put(configClass, configClass);
}

// 处理任何@componentscan 注释
Set<AnnotationAttributes> componentScans = AnnotationConfigUtils.attributesForRepeatable(
    sourceClass.getMetadata(), ComponentScans.class, ComponentScan.class);
if (!componentScans.isEmpty() &&
    !this.conditionEvaluator.shouldSkip(sourceClass.getMetadata(), ConfigurationPhase.REGISTER_BEAN)) {
    for (AnnotationAttributes componentScan : componentScans) {
        // 配置类使用@componentscan 注释——立即执行扫描
        Set<BeanDefinitionHolder> scannedBeanDefinitions =
                this.componentScanParser.parse(componentScan, sourceClass.getMetadata().getClassName());
        // 检查任何进一步配置类的扫描定义集，并在需要时递归地解析
        for (BeanDefinitionHolder holder : scannedBeanDefinitions) {
            BeanDefinition bdCand = holder.getBeanDefinition().getOriginatingBeanDefinition();
            if (bdCand == null) {
                bdCand = holder.getBeanDefinition();
            }
            if (ConfigurationClassUtils.checkConfigurationClassCandidate(bdCand, this.metadataReaderFactory)) {
                parse(bdCand.getBeanClassName(), holder.getBeanName());
            }
        }
    }
}

public Set<BeanDefinitionHolder> parse(AnnotationAttributes componentScan, final String declaringClass) {
    // 类扫描工具
    ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(this.registry,
            componentScan.getBoolean("useDefaultFilters"), this.environment, this.resourceLoader);

    Class<? extends BeanNameGenerator> generatorClass = componentScan.getClass("nameGenerator");
    boolean useInheritedGenerator = (BeanNameGenerator.class == generatorClass);
    scanner.setBeanNameGenerator(useInheritedGenerator ? this.beanNameGenerator :
            BeanUtils.instantiateClass(generatorClass));

    ScopedProxyMode scopedProxyMode = componentScan.getEnum("scopedProxy");
    if (scopedProxyMode != ScopedProxyMode.DEFAULT) {
        scanner.setScopedProxyMode(scopedProxyMode);
    }
    else {
        Class<? extends ScopeMetadataResolver> resolverClass = componentScan.getClass("scopeResolver");
        scanner.setScopeMetadataResolver(BeanUtils.instantiateClass(resolverClass));
    }
	// 获取扫描包路径的.class字节码文件
    scanner.setResourcePattern(componentScan.getString("resourcePattern"));
	// 添加包括类型过滤器
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("includeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addIncludeFilter(typeFilter);
        }
    }
    // 添加排除类型过滤器
    for (AnnotationAttributes filter : componentScan.getAnnotationArray("excludeFilters")) {
        for (TypeFilter typeFilter : typeFiltersFor(filter)) {
            scanner.addExcludeFilter(typeFilter);
        }
    }
	// 设置懒加载状态
    boolean lazyInit = componentScan.getBoolean("lazyInit");
    if (lazyInit) {
        scanner.getBeanDefinitionDefaults().setLazyInit(true);
    }
	// 把包componentScan扫描获取的Bean全部放入这个对象中
    Set<String> basePackages = new LinkedHashSet<>();
    // 获取componentScan扫描包路径的表达式
    String[] basePackagesArray = componentScan.getStringArray("basePackages");
    for (String pkg : basePackagesArray) {
        String[] tokenized = StringUtils.tokenizeToStringArray(this.environment.resolvePlaceholders(pkg),
                ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
        Collections.addAll(basePackages, tokenized);
    }
    for (Class<?> clazz : componentScan.getClassArray("basePackageClasses")) {
        basePackages.add(ClassUtils.getPackageName(clazz));
    }
    
    if (basePackages.isEmpty()) {
        // 获取本类位置的package包的路径
        basePackages.add(ClassUtils.getPackageName(declaringClass));
    }
	// 排除掉本类的路径, 防止重复注册
    scanner.addExcludeFilter(new AbstractTypeHierarchyTraversingFilter(false, false) {
        @Override
        protected boolean matchClassName(String className) {
            return declaringClass.equals(className);
        }
    });
    // 做扫描, 返回注解扫描出来的所有类, 并且注册扫描出来的组件到容器中
    return scanner.doScan(StringUtils.toStringArray(basePackages));
}

private Set<BeanDefinition> scanCandidateComponents(String basePackage) {
    Set<BeanDefinition> candidates = new LinkedHashSet<>();
    try {
        // 组装 com.**.class
        String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
                resolveBasePackage(basePackage) + '/' + this.resourcePattern;
        // 获取所有子类的class字节码
        Resource[] resources = getResourcePatternResolver().getResources(packageSearchPath);
        boolean traceEnabled = logger.isTraceEnabled();
        boolean debugEnabled = logger.isDebugEnabled();
        // 遍历所有字节码文件资源
        for (Resource resource : resources) {
            if (traceEnabled) {
                logger.trace("Scanning " + resource);
            }
            if (resource.isReadable()) {
                try {
                    MetadataReader metadataReader = getMetadataReaderFactory().getMetadataReader(resource);
                    if (isCandidateComponent(metadataReader)) {
                        ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
                        sbd.setResource(resource);
                        sbd.setSource(resource);
                        if (isCandidateComponent(sbd)) {
                            if (debugEnabled) {
                                logger.debug("Identified candidate component class: " + resource);
                            }
                            candidates.add(sbd);
                        }
                        else {
                            if (debugEnabled) {
                                logger.debug("Ignored because not a concrete top-level class: " + resource);
                            }
                        }
                    }
                    else {
                        if (traceEnabled) {
                            logger.trace("Ignored because not matching any filter: " + resource);
                        }
                    }
                }
                catch (Throwable ex) {
                    throw new BeanDefinitionStoreException(
                            "Failed to read candidate component class: " + resource, ex);
                }
            }
            else {
                if (traceEnabled) {
                    logger.trace("Ignored because not readable: " + resource);
                }
            }
        }
    }
    catch (IOException ex) {
        throw new BeanDefinitionStoreException("I/O failure during classpath scanning", ex);
    }
    return candidates;
}

protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Assert.notEmpty(basePackages, "At least one base package must be specified");
    // 将我们需要扫描到的类加入到这里, 比如UserDao这种
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<>();
    // 遍历前面获取的所有.class字节码文件的路径
    for (String basePackage : basePackages) {
        // 判断是否是我们需要的组件, 比如UserDao UserService UserController 这种, 不包括配置类
        Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
        for (BeanDefinition candidate : candidates) {
            // 获取scope, 并且设置scope
            ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
            candidate.setScope(scopeMetadata.getScopeName());
            // 获取bean的名字, 这里的名字不包含包名
            String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
            // 设置默认Beandefinition的默认属性, 例如lazy InitMethodName AutowireMode DestroyMethodName 这类属性
            if (candidate instanceof AbstractBeanDefinition) {
                postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
            }
            if (candidate instanceof AnnotatedBeanDefinition) {
                // 设置lazy Primary dependsOn role description
                AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
            }
            if (checkCandidate(beanName, candidate)) {
                BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
                definitionHolder =
                        AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
                beanDefinitions.add(definitionHolder);
                // 注册UserDao这样的组件
                registerBeanDefinition(definitionHolder, this.registry);
            }
        }
    }
    return beanDefinitions;
}

(6) 注册拦截Bean创建的Bean处理器

注册bean的后置处理器

registerBeanPostProcessors(beanFactory)

org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, org.springframework.context.support.AbstractApplicationContext)

protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    // 这个beanFactory就是DefaultListableBeanFactory, 这个this就是AnnotationConfigApplicationContext
    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
}

注册PostProcessors

// 根据类型获取容器中的postProcessor
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

根据不同PostProcessor继承的接口把不同的PostProcess放入不同的集合

List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
    if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        priorityOrderedPostProcessors.add(pp);
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
            internalPostProcessors.add(pp);
        }
    }
    else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
        orderedPostProcessorNames.add(ppName);
    }
    else {
        nonOrderedPostProcessorNames.add(ppName);
    }
}

// 注册继承了priority的PostProcessor
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

// 注册实现了Ordered的PostProcessor
List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String ppName : orderedPostProcessorNames) {
    BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    orderedPostProcessors.add(pp);
    if (pp instanceof MergedBeanDefinitionPostProcessor) {
        internalPostProcessors.add(pp);
    }
}
sortPostProcessors(orderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, orderedPostProcessors);

// 注册所有常规的PostProcessor
List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String ppName : nonOrderedPostProcessorNames) {
    BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
    nonOrderedPostProcessors.add(pp);
    if (pp instanceof MergedBeanDefinitionPostProcessor) {
        internalPostProcessors.add(pp);
    }
}
registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

// 注册内部类
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);

// 将检测内部 bean 的后处理器重新注册为 ApplicationListeners，将其移动到处理器链的末尾(用于接收代理等)。
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));

(7) 为此上下文初始化消息源

initMessageSource();

内部做了个消息源的单例的注册

(8) 为此上下文初始化事件多播器

this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
			beanFactory.registerSingleton(APPLICATION_EVENT_MULTICASTER_BEAN_NAME, this.applicationEventMulticaster);

(9) 在特定上下文子类中初始化其他特殊bean

	protected void onRefresh() throws BeansException {
		// For subclasses: do nothing by default.
	}

(10) 检查侦听器bean并注册它们

registerListeners();

protected void registerListeners() {
    // 先注册静态指定的侦听器。
    for (ApplicationListener<?> listener : getApplicationListeners()) {
        getApplicationEventMulticaster().addApplicationListener(listener);
    }

    // 不要在这里初始化 FactoryBeans: 我们需要保留所有未初始化的常规 beans，以便将后处理器应用于它们！
    // 这里其实就是拿到application中的监听器
    String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
    for (String listenerBeanName : listenerBeanNames) {
        getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
    }

    // 发布早期的应用程序事件，现在我们终于有了一个多主机..
    Set<ApplicationEvent> earlyEventsToProcess = this.earlyApplicationEvents;
    this.earlyApplicationEvents = null;
    if (earlyEventsToProcess != null) {
        for (ApplicationEvent earlyEvent : earlyEventsToProcess) {
            getApplicationEventMulticaster().multicastEvent(earlyEvent);
        }
    }
}

(11) 实例化所有剩余的（非延迟初始化）单例

finishBeanFactoryInitialization(beanFactory);

beanFactory.preInstantiateSingletons(); // 里面最重要的方法

public void preInstantiateSingletons() throws BeansException {
    if (logger.isTraceEnabled()) {
        logger.trace("Pre-instantiating singletons in " + this);
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.
    // 里面存入beandefinition的名字
    List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    // 遍历这个definitionBean的名字
    for (String beanName : beanNames) {
        // 获取BeanDefinition
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            // 是工厂类么?
            if (isFactoryBean(beanName)) {
                // 根据完整的包名获取对象 FACTORY_BEAN_PREFIX = &
                Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
                if (bean instanceof FactoryBean) {
                    final FactoryBean<?> factory = (FactoryBean<?>) bean;
                    boolean isEagerInit;
                    if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                        isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
                                        ((SmartFactoryBean<?>) factory)::isEagerInit,
                                getAccessControlContext());
                    }
                    else {
                        isEagerInit = (factory instanceof SmartFactoryBean &&
                                ((SmartFactoryBean<?>) factory).isEagerInit());
                    }
                    if (isEagerInit) {
                        getBean(beanName);
                    }
                }
            }
            else {
                // 根据这个bean获取对象, 如果没有则创建这个bean
                getBean(beanName);
            }
        }
    }

    // 触发所有适用bean的初始化后回调...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                    smartSingleton.afterSingletonsInstantiated();
                    return null;
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

(12) 最后一步：发布相应的事件

(13) 在Spring的核心中重置常见的自省缓存，因为我们可能再也不需要单例bean的元数据了

来自为知笔记(Wiz)