1. 为什么要有 springboot
1.1spring 的优缺点
长处：提供了 ioc 和 aop 等弱小的性能让开发人员专一业务代码
毛病：配置简单，我的项目依赖繁琐，依赖版本稍有不对就会造成兼容问题
2.springboot 如何解决这些问题
2.1 起步依赖 ：只需依赖一个我的项目就可达到 spring 依赖多个包的性能，行将具备某种性能的坐标打包到一起。
两个外围依赖 spring-boot-starter-parent 和spring-boot-starter-web：
spring-boot-starter-parent 指定 jar 包版本
spring-boot-starter-web 指定 web 开发 jar 包
2.2 主动配置：只需引入相干的包，springboot 会在启动时将这些配置的 bean 给初始化
通过在 main 函数加上注解 @SpringBootApplication，该注解次要蕴含三个要害注解
· @configuration注解：代表它是一个配置类，咱们能够在该类中申明一些办法，返回 bean
· @EnableAutoConfiguration：初始化 bean
• @Import(AutoConfigurationImportSelector.class)：实现主动配置的性能，从 classpath 下所有 jar 包的 META-INF\spring-autoconfigure-metadata.properties 拿到指定的 bean 初始化限度条件，而后从 spring.factories 里拿到指定的类初始化 bean，进行初始化。
其余注解：
• @AutoConfigurationPackage：实例化启动类所在包上面的所有 bean
· @ComponentScan: 指定扫描包范畴，配和 @AutoConfigurationPackage 应用，可过滤不想初始化的 bean
3. 具体实现
看启动函数：
@SpringBootApplication public class DemoApplication
{public static void main(String[] args)
{SpringApplication.run(DemoApplication.class, args);
}
}3.1 构造函数
public SpringApplication(ResourceLoader resourceLoader, Object... sources) {
this.resourceLoader = resourceLoader;
initialize(sources);
}进入 initialize 办法
private void initialize(Object[] sources) {if (sources != null && sources.length > 0) {this.sources.addAll(Arrays.asList(sources));
}
this.webEnvironment = deduceWebEnvironment();
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();}进入 deduceWebEnvironment
private boolean deduceWebEnvironment() {for (String className : WEB_ENVIRONMENT_CLASSES) {if (!ClassUtils.isPresent(className, null)) {return false;}
}
return true;
}此办法是用来判断以后利用是什么类型：
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };须要下面两个类都存在才阐明以后是个 web 利用.
再看 setInitializers 和 setListeners 办法，都调用了 getSpringFactoriesInstances 办法：
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<String>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}getSpringFactoriesInstances 办法是扫描门路下所有 META-INF\spring.factories 里
合乎 type 参数指定的接口的实现类并实例化，而后排序。
最初 this.mainApplicationClass = deduceMainApplicationClass()找出启动 main 函数在的主类。
3.2run 办法
public ConfigurableApplicationContext run(String... args) {StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.started();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
analyzers = new FailureAnalyzers(context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
listeners.finished(context, null);
stopWatch.stop();
if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
return context;
}
catch (Throwable ex) {handleRunFailure(context, listeners, analyzers, ex);
throw new IllegalStateException(ex);
}
}首先看 getRunListeners 办法：
private SpringApplicationRunListeners getRunListeners(String[] args) {Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}同样是找到并实例化 SpringApplicationRunListener 的实现类；
再看 listeners.started()做了什么：
一路跟进去
最终调用了 listener.onApplicationEvent(event)办法，该办法有很多子类的实现，内容大略就是做一些筹备工作，比方 org.springframework.boot.context.logging.LoggingApplicationListener 做的就是
private void onApplicationStartedEvent(ApplicationStartedEvent event) {
this.loggingSystem = LoggingSystem
.get(event.getSpringApplication().getClassLoader());
this.loggingSystem.beforeInitialize();}日志初始化的一些筹备工作。
接下来看
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);初始化 main 函数的参数；
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments); private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
if (isWebEnvironment(environment) && !this.webEnvironment) {environment = convertToStandardEnvironment(environment);
}
return environment;
}进入 getOrCreateEnvironment：
private ConfigurableEnvironment getOrCreateEnvironment() {if (this.environment != null) {return this.environment;}
if (this.webEnvironment) {return new StandardServletEnvironment();
}
return new StandardEnvironment();}个别都是 webEnvironment，所以返回 new StandardServletEnvironment()；
protected void configureEnvironment(ConfigurableEnvironment environment,
String[] args) {configurePropertySources(environment, args);
configureProfiles(environment, args);
}
protected void configurePropertySources(ConfigurableEnvironment environment,
String[] args) {MutablePropertySources sources = environment.getPropertySources();
if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
}
if (this.addCommandLineProperties && args.length > 0) {
String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
if (sources.contains(name)) {PropertySource<?> source = sources.get(name);
CompositePropertySource composite = new CompositePropertySource(name);
composite.addPropertySource(new SimpleCommandLinePropertySource(name + "-" + args.hashCode(), args));
composite.addPropertySource(source);
sources.replace(name, composite);
}
else {sources.addFirst(new SimpleCommandLinePropertySource(args));
}
}
}defaultProperties 是额定属性配置，能够在结构 SpringBootApplication 时通过 setDefaultProperties 设置；
如果配置了 args，且命令行有名为 commandLineArgs 的参数，则会用命令行参数替换或新增该 PropertySource。
再看 configureProfiles，我的版本是个空办法（spring-boot-2.7.3）
看了下其余版本的，大略就是读取 properties 里的 key 为 spring.profiles.active 的配置项，配置到 Environment。
持续看 ConfigurationPropertySources.attach(environment)
/**
* Attach a {@link ConfigurationPropertySource} support to the specified
* {@link Environment}. Adapts each {@link PropertySource} managed by the environment
* to a {@link ConfigurationPropertySource} and allows classic
* {@link PropertySourcesPropertyResolver} calls to resolve using
* {@link ConfigurationPropertyName configuration property names}.
* <p>
* The attached resolver will dynamically track any additions or removals from the
* underlying {@link Environment} property sources.
* @param environment the source environment (must be an instance of
* {@link ConfigurableEnvironment})
* @see #get(Environment)
*/
public static void attach(Environment environment) {Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
PropertySource<?> attached = getAttached(sources);
if (attached == null || !isUsingSources(attached, sources)) {
attached = new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
new SpringConfigurationPropertySources(sources));
}
sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
sources.addFirst(attached);
}该办法将 ConfigurationPropertySource 和 environment 绑定起来。
listeners.environmentPrepared(bootstrapContext, environment)办法为监听器筹备环境，过程有点简单，当前再看。
DefaultPropertiesPropertySource.moveToEnd(environment)将默认环境移到最初，这样优先级最高？
bindToSpringApplication(environment)将环境和主类绑定。
if (!this.isCustomEnvironment) {EnvironmentConverter environmentConverter = new EnvironmentConverter(getClassLoader());
environment = environmentConverter.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}将环境转化为规范环境
environment 为 ApplicationServletEnvironment，是 StandEnvironment 的子类，不必转。
ConfigurationPropertySources.attach(environment) 再绑定一次环境和 source。
prepareEnvironment 完结了，再看 configureIgnoreBeanInfo(environment)：
private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {if (System.getProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {
Boolean ignore = environment.getProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME,
Boolean.class, Boolean.TRUE);
System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME, ignore.toString());
}
}
将 environment 的 spring.beaninfo.ignore 的值设置到零碎属性。
Banner printedBanner = printBanner(environment);
打印 banner，
. ____ _ __ _ _
/\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
(()\___ | '_ |'_| | '_ \/ _` | \ \ \ \
\\/ ___)| |_)| | | | | || (_| |) ) ) )
' |____| .__|_| |_|_| |_\__, | / / / /
=========|_|==============|___/=/_/_/_/
:: Spring Boot :: (v2.2.5.RELEASE)如上图所示的，是咱们每次启动 SpringBoot 我的项目时就会在控制器输入的内容，这个就是 Banner 。这部分代码不重要。context = createApplicationContext();
/**
* {@link ApplicationContextFactory} registered in {@code spring.factories} to support
* {@link AnnotationConfigServletWebServerApplicationContext}.
*/
static class Factory implements ApplicationContextFactory {
@Override
public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {return (webApplicationType != WebApplicationType.SERVLET) ? null
: new AnnotationConfigServletWebServerApplicationContext();}
}创立了一个 AnnotationConfigServletWebServerApplicationContext。
AnnotationConfigServletWebServerApplicationContext 继承自 GenericApplicationContext，
/**
* Create a new GenericApplicationContext.
* @see #registerBeanDefinition
* @see #refresh
*/
public GenericApplicationContext() {this.beanFactory = new DefaultListableBeanFactory();
}
父类实例化的时候创立了一个 DefaultListableBeanFactory。
子类是泪花的时候创立了 AnnotatedBeanDefinitionReader 和 ClassPathBeanDefinitionScanner，这两个类是用来读取 condition 注解和定义哪些类应该被实例化（@Component，@Service，@Resources 这种）
/**
* Create a new {@link AnnotationConfigServletWebServerApplicationContext} with the
* given {@code DefaultListableBeanFactory}. The context needs to be populated through
* {@link #register} calls and then manually {@linkplain #refresh refreshed}.
* @param beanFactory the DefaultListableBeanFactory instance to use for this context
*/
public AnnotationConfigServletWebServerApplicationContext(DefaultListableBeanFactory beanFactory) {super(beanFactory);
this.reader = new AnnotatedBeanDefinitionReader(this);
this.scanner = new ClassPathBeanDefinitionScanner(this);
}接下来 prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner)：
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
// 注入环境属性
context.setEnvironment(environment);
// 上下文后置解决
this.postProcessApplicationContext(context);
// 欠缺初始化类的属性
this.applyInitializers(context);
// 发送监听事件
listeners.contextPrepared(context);
// 日志
if (this.logStartupInfo) {this.logStartupInfo(context.getParent() == null);
this.logStartupProfileInfo(context);
}
// 注册传入的配置参数为 bean，这里将传入的参数封装成 applicationArguments，外部相似命令行
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
//banner 打印
if (printedBanner != null) {beanFactory.registerSingleton("springBootBanner", printedBanner);
}
// 这里默认状况下 bean 定义不容许反复
if (beanFactory instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// 默认不开启提早加载
if (this.lazyInitialization) {context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
}
// 获取全副的资源
// 这里获取了启动类的资源和 以后 SpringApplication 中的 source 资源。// 到目前来说实际上只有启动类资源
Set<Object> sources = this.getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
this.load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}后置解决 context
protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
// 是否自定义 bean 名称生成类
if (this.beanNameGenerator != null) {context.getBeanFactory().registerSingleton("org.springframework.context.annotation.internalConfigurationBeanNameGenerator", this.beanNameGenerator);
}
// 是否指定类加载器
if (this.resourceLoader != null) {if (context instanceof GenericApplicationContext) {((GenericApplicationContext)context).setResourceLoader(this.resourceLoader);
}
if (context instanceof DefaultResourceLoader) {((DefaultResourceLoader)context).setClassLoader(this.resourceLoader.getClassLoader());
}
}
// 是否增加数据转换器
// 在初始化环境对象的时候也有用到，这里能够间接通过 context.getEnvironment().getConversionService()获取到
if (this.addConversionService) {context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
}
}剩下的都是做一些筹备工作。
refreshContext（重点）：
@Override
public void refresh() throws BeansException, IllegalStateException {synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();}
catch (BeansException ex) {if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization -" +
"cancelling refresh attempt:" + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();}
}
}首先看 prepareRefresh()办法：
@Override
protected void prepareRefresh() {this.scanner.clearCache();
super.prepareRefresh();}scnner 清了缓存，父类 prepareRefresh 办法什么都没做；
再看 obtainFreshBeanFactory：
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {refreshBeanFactory();
ConfigurableListableBeanFactory beanFactory = getBeanFactory();
if (logger.isDebugEnabled()) {logger.debug("Bean factory for" + getDisplayName() + ":" + beanFactory);
}
return beanFactory;
}
@Override
protected final void refreshBeanFactory() throws IllegalStateException {if (!this.refreshed.compareAndSet(false, true)) {
throw new IllegalStateException("GenericApplicationContext does not support multiple refresh attempts: just call'refresh'once");
}
this.beanFactory.setSerializationId(getId());
}
@Override
public final ConfigurableListableBeanFactory getBeanFactory() {return this.beanFactory;}
refreshBeanFactory 办法设置了一下 id，getBeanFactory 办法获取下面创立的 factory。
接着看 prepareBeanFactory 办法：
/**
* Configure the factory's standard context characteristics,
* such as the context's ClassLoader and post-processors.
* @param beanFactory the BeanFactory to configure
*/
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
if (!shouldIgnoreSpel) {beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
}
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
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);
beanFactory.ignoreDependencyInterface(ApplicationStartupAware.class);
// BeanFactory interface not registered as resolvable type in a plain factory.
// MessageSource registered (and found for autowiring) as a bean.
beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
// Register early post-processor for detecting inner beans as ApplicationListeners.
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
// Detect a LoadTimeWeaver and prepare for weaving, if found.
if (!NativeDetector.inNativeImage() && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
// Set a temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
// Register default environment beans.
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());
}
if (!beanFactory.containsLocalBean(APPLICATION_STARTUP_BEAN_NAME)) {beanFactory.registerSingleton(APPLICATION_STARTUP_BEAN_NAME, getApplicationStartup());
}
}首先疏忽一些主动注入；而后减少一些主动注入的依赖（一个接口有多个实现类时，用这里指定的实现类）；而后减少 ApplicationListenerDetector 的 BeanPostProcessor，而后注册一些环境单例 bean。
而后再看 postProcessBeanFactory：
这是个空办法，由子类实现，以后实现的子类是 AnnotationConfigServletWebServerApplicationContext：
@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {super.postProcessBeanFactory(beanFactory);
if (this.basePackages != null && this.basePackages.length > 0) {this.scanner.scan(this.basePackages);
}
if (!this.annotatedClasses.isEmpty()) {this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));
}
}
/**super.postProcessBeanFactory(beanFactory)：
/**
* Register ServletContextAwareProcessor.
* @see ServletContextAwareProcessor
*/
@Override
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {beanFactory.addBeanPostProcessor(new WebApplicationContextServletContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
registerWebApplicationScopes();}减少了一个后置处理器，疏忽主动注入；
再看 registerWebApplicationScopes：
/**
* Register web-specific scopes ("request", "session", "globalSession", "application")
* with the given BeanFactory, as used by the WebApplicationContext.
* @param beanFactory the BeanFactory to configure
* @param sc the ServletContext that we're running within
*/
public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory,
@Nullable ServletContext sc) {beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope());
beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope());
if (sc != null) {ServletContextScope appScope = new ServletContextScope(sc);
beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope);
// Register as ServletContext attribute, for ContextCleanupListener to detect it.
sc.setAttribute(ServletContextScope.class.getName(), appScope);
}
beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());
if (jsfPresent) {FacesDependencyRegistrar.registerFacesDependencies(beanFactory);
}
}将 web 申请的几种类型注册；
再回到后面：
if (this.basePackages != null && this.basePackages.length > 0) {this.scanner.scan(this.basePackages);
}
if (!this.annotatedClasses.isEmpty()) {this.reader.register(ClassUtils.toClassArray(this.annotatedClasses));
}此处 scan 不是扫描 @ComponentScan 指定的包，意义暂不明；
接着看 invokeBeanFactoryPostProcessors（重点），正文在代码中.
public static void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set<String> processedBeans = new HashSet<>();
// 如果 beanFactory 是 BeanDefinitionRegistry，那先调用 beanFactoryPostProcessors 中和 beanFactory 存在的
// 类型为 BeanDefinitionRegistryPostProcessor 的 postProcessBeanDefinitionRegistry
// 而后调用 beanFactoryPostProcessors 的 postprocessBeanFactory 办法
// 优先级 PriorityOrdered->Ordered-> 其余
if (beanFactory instanceof BeanDefinitionRegistry) {BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {if (!processedBeans.contains(ppName)) {currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();}
// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// Invoke factory processors registered with the context instance.
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// 而后调用 beanFacyory 中类型为 BeanFactoryPostProcessor 的 postProcessBeanFactory 办法，因为 BeanDefinitionRegistryPostProcessor 是 BeanFactoryPostProcessor 的子类
// 所以第一步中解决过的要过滤
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
List<String> orderedPostProcessorNames = new ArrayList<>();
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {if (processedBeans.contains(ppName)) {// skip - already processed in first phase above}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {orderedPostProcessorNames.add(ppName);
}
else {nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>();
for (String postProcessorName : orderedPostProcessorNames) {orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
for (String postProcessorName : nonOrderedPostProcessorNames) {nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();}
invokeBeanFactoryPostProcessors 办法完结，就是调用了 beanFactoryPostProcessors，接着看 registerBeanPostProcessors：
/*
Register bean processors that intercept bean creation.
注册 BeanPostProcessor（Bean 的后置处理器），在创立 bean 的前后等执行
*/
public static void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
// 获取所有 postProcessor 的名称
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
// Register BeanPostProcessorChecker that logs an info message when
// a bean is created during BeanPostProcessor instantiation, i.e. when
// a bean is not eligible for getting processed by all BeanPostProcessors.
int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
// 存储 PriorityOrdered.class 的 postProcessor
List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
// 存储 Ordered.class 的 postProcessor
List<String> orderedPostProcessorNames = new ArrayList<>();
// 存储其余的 postProcessor
List<String> nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {
// 优先级最高
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
priorityOrderedPostProcessors.add(pp);
if (pp instanceof MergedBeanDefinitionPostProcessor) {internalPostProcessors.add(pp);
}
}
// 优先级第二
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {orderedPostProcessorNames.add(ppName);
}
else {
// 优先级最末
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, register the BeanPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
// 注册 PriorityOrdered.class 的 BeanPostProcessors，所谓注册就是外部的 List<BeanPostProcessor> beanPostProcessors 对象加上这个 BeanPostProcessor
// 在这之前这个 bean 只作为一个一般 bean 存在于 beanFactory
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
// Next, register the BeanPostProcessors that implement Ordered.
// 注册 Ordered.class 的 BeanPostProcessors，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);
// Now, register all regular BeanPostProcessors.
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);
// Finally, re-register all internal BeanPostProcessors.
// 注册其余的 BeanPostProcessors，sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);
// Re-register post-processor for detecting inner beans as ApplicationListeners,
// moving it to the end of the processor chain (for picking up proxies etc).
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
上面是 initMessageSource，不是重点，先不看
/*
Initialize message source for this context.
初始化 MessageSource 组件（做国际化性能；音讯绑定，音讯解析）；*/
initMessageSource();
initApplicationEventMulticaster 也不是重点，先不看
/*
Initialize event multicaster for this context.
初始化事件派发器
*/
initApplicationEventMulticaster();onFresh，空办法，交给子类实现
/*
Initialize other special beans in specific context subclasses.
子类重写这个办法，在容器刷新的时候能够自定义逻辑；如创立 Tomcat，Jetty 等 WEB 服务器
*/
onRefresh();
registerListener，先不看
/*
Check for listener beans and register them.
注册利用的监听器。就是注册实现了 ApplicationListener 接口的监听器 bean
*/
registerListeners();finishBeanFactoryInitialization（重点）：
/*
Instantiate all remaining (non-lazy-init) singletons.
初始化所有剩下的非懒加载的单例 bean
初始化创立非懒加载形式的单例 Bean 实例（未设置属性）填充属性
初始化办法调用（比方调用 afterPropertiesSet 办法、init-method 办法）调用 BeanPostProcessor（后置处理器）对实例 bean 进行后置解决
*/
finishBeanFactoryInitialization(beanFactory);
/**
* Finish the initialization of this context's bean factory,
* initializing all remaining singleton beans.
* 完结 bean factory 的初始化工作
* 实例化所有单例 bean
*/
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
if (!beanFactory.hasEmbeddedValueResolver()) {beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
// 实例化所有立刻加载的单例 bean
beanFactory.preInstantiateSingletons();}
@Override
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.
// 所有 bean 的名字
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
// 触发所有非提早加载单例 bean 的初始化，次要步骤为 getBean
for (String beanName : beanNames) {
// 合并父 BeanDefinition 对象
// map.get(beanName)
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {if (isFactoryBean(beanName)) {Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
// 如果是 FactoryBean 则加 &
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 {
// 实例化以后 bean
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
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();
}
}
}
}
看 getBean 办法，调用的是 org.springframework.beans.factory.support.AbstractBeanFactory#getBean(java.lang.String)：
@Override
public Object getBean(String name) throws BeansException {return doGetBean(name, null, null, false);
}
/**
* Return an instance, which may be shared or independent, of the specified bean.
* @param name the name of the bean to retrieve
* @param requiredType the required type of the bean to retrieve
* @param args arguments to use when creating a bean instance using explicit arguments
* (only applied when creating a new instance as opposed to retrieving an existing one)
* @param typeCheckOnly whether the instance is obtained for a type check,
* not for actual use
* @return an instance of the bean
* @throws BeansException if the bean could not be created
*/
@SuppressWarnings("unchecked")
protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
@Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {
// 解析 beanName 如果以 & 结尾去掉 & 结尾，如果是别名获取到真正的名字
final String beanName = transformedBeanName(name);
Object bean;
// 单纯了解尝试从缓存中获取 bean
Object sharedInstance = getSingleton(beanName);
// 如果曾经存在则返回
if (sharedInstance != null && args == null) {if (logger.isTraceEnabled()) {if (isSingletonCurrentlyInCreation(beanName)) {
logger.trace("Returning eagerly cached instance of singleton bean'" + beanName +
"'that is not fully initialized yet - a consequence of a circular reference");
}
else {logger.trace("Returning cached instance of singleton bean'" + beanName + "'");
}
}
// 针对 FactoryBean 的解决
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
// 如果是 prototype 类型且开启容许循环依赖，则抛出异样
if (isPrototypeCurrentlyInCreation(beanName)) {throw new BeanCurrentlyInCreationException(beanName);
}
// Check if bean definition exists in this factory.
// 查看父工厂中是否存在该对象
BeanFactory parentBeanFactory = getParentBeanFactory();
if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
// Not found -> check parent.
String nameToLookup = originalBeanName(name);
if (parentBeanFactory instanceof AbstractBeanFactory) {return ((AbstractBeanFactory) parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
}
else if (args != null) {
// Delegation to parent with explicit args.
return (T) parentBeanFactory.getBean(nameToLookup, args);
}
else if (requiredType != null) {
// No args -> delegate to standard getBean method.
return parentBeanFactory.getBean(nameToLookup, requiredType);
}
else {return (T) parentBeanFactory.getBean(nameToLookup);
}
}
if (!typeCheckOnly) {markBeanAsCreated(beanName);
}
try {
// 合并父子 bean 属性
final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
checkMergedBeanDefinition(mbd, beanName, args);
// Guarantee initialization of beans that the current bean depends on.
// 解决 dependsOn 配置
String[] dependsOn = mbd.getDependsOn();
if (dependsOn != null) {for (String dep : dependsOn) {if (isDependent(beanName, dep)) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Circular depends-on relationship between'" + beanName + "'and'" + dep + "'");
}
registerDependentBean(dep, beanName);
try {getBean(dep);
}
catch (NoSuchBeanDefinitionException ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"'"+ beanName +"' depends on missing bean '"+ dep +"'", ex);
}
}
}
// 创立单例 bean
if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {
try {
// 创立 bean
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
// It's a prototype -> create a new instance.
Object prototypeInstance = null;
try {beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
if (scope == null) {throw new IllegalStateException("No Scope registered for scope name'" + scopeName + "'");
}
try {Object scopedInstance = scope.get(beanName, () -> {beforePrototypeCreation(beanName);
try {return createBean(beanName, mbd, args);
}
finally {afterPrototypeCreation(beanName);
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
catch (IllegalStateException ex) {
throw new BeanCreationException(beanName,
"Scope'" + scopeName + "'is not active for the current thread; consider" +
"defining a scoped proxy for this bean if you intend to refer to it from a singleton",
ex);
}
}
}
catch (BeansException ex) {cleanupAfterBeanCreationFailure(beanName);
throw ex;
}
}
// Check if required type matches the type of the actual bean instance.
if (requiredType != null && !requiredType.isInstance(bean)) {
try {T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
if (convertedBean == null) {throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
return convertedBean;
}
catch (TypeMismatchException ex) {if (logger.isTraceEnabled()) {
logger.trace("Failed to convert bean'" + name + "'to required type'" +
ClassUtils.getQualifiedName(requiredType) + "'", ex);
}
throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
}
}
return (T) bean;
}
先从缓存中获取：
// 单纯了解尝试从缓存中获取 bean
Object sharedInstance = getSingleton(beanName);
/**
* Return the (raw) singleton object registered under the given name.
* <p>Checks already instantiated singletons and also allows for an early
* reference to a currently created singleton (resolving a circular reference).
* @param beanName the name of the bean to look for
* @param allowEarlyReference whether early references should be created or not
* @return the registered singleton object, or {@code null} if none found
*/
@Nullable
protected Object getSingleton(String beanName, boolean allowEarlyReference) {Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {synchronized (this.singletonObjects) {singletonObject = this.earlySingletonObjects.get(beanName);
if (singletonObject == null && allowEarlyReference) {ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
if (singletonFactory != null) {singletonObject = singletonFactory.getObject();
this.earlySingletonObjects.put(beanName, singletonObject);
this.singletonFactories.remove(beanName);
}
}
}
}
return singletonObject;
}这里用到了三级缓存，一级一级获取，如果从三级缓存获取到了则放入二级缓存，从三级缓存移除。
如果获取不到，则调用 getSingleton 办法：
// 创立单例 bean
if (mbd.isSingleton()) {sharedInstance = getSingleton(beanName, () -> {
try {
// 创立 bean
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
// Explicitly remove instance from singleton cache: It might have been put there
// eagerly by the creation process, to allow for circular reference resolution.
// Also remove any beans that received a temporary reference to the bean.
destroySingleton(beanName);
throw ex;
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
/**
* Return the (raw) singleton object registered under the given name,
* creating and registering a new one if none registered yet.
* @param beanName the name of the bean
* @param singletonFactory the ObjectFactory to lazily create the singleton
* with, if necessary
* @return the registered singleton object
*/
public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {Assert.notNull(beanName, "Bean name must not be null");
synchronized (this.singletonObjects) {Object singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {
// 是否正在销毁，异样
if (this.singletonsCurrentlyInDestruction) {
throw new BeanCreationNotAllowedException(beanName,
"Singleton bean creation not allowed while singletons of this factory are in destruction" +
"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
}
if (logger.isDebugEnabled()) {logger.debug("Creating shared instance of singleton bean'" + beanName + "'");
}
// 验证完要真正开始创建对象，先标识该 bean 正在被创立，因为 spingbean 创立过程简单，步骤很多，须要标识
beforeSingletonCreation(beanName);
boolean newSingleton = false;
boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
if (recordSuppressedExceptions) {this.suppressedExceptions = new LinkedHashSet<>();
}
try {
// 传进来的调用，lamda 表达式应用
singletonObject = singletonFactory.getObject();
newSingleton = true;
}
catch (IllegalStateException ex) {
// Has the singleton object implicitly appeared in the meantime ->
// if yes, proceed with it since the exception indicates that state.
singletonObject = this.singletonObjects.get(beanName);
if (singletonObject == null) {throw ex;}
}
catch (BeanCreationException ex) {if (recordSuppressedExceptions) {for (Exception suppressedException : this.suppressedExceptions) {ex.addRelatedCause(suppressedException);
}
}
throw ex;
}
finally {if (recordSuppressedExceptions) {this.suppressedExceptions = null;}
afterSingletonCreation(beanName);
}
if (newSingleton) {addSingleton(beanName, singletonObject);
}
}
return singletonObject;
}
}
看看 singletonFactory.getObject()办法，也就是传参的 lamda 表达式的 createBean（）办法：
// 传进来的调用，lamda 表达式应用
singletonObject = singletonFactory.getObject();
/**
* Central method of this class: creates a bean instance,
* populates the bean instance, applies post-processors, etc.
* @see #doCreateBean
*/
@Override
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
throws BeanCreationException {if (logger.isTraceEnabled()) {logger.trace("Creating instance of bean'" + beanName + "'");
}
// 拿到 Bd
RootBeanDefinition mbdToUse = mbd;
// Make sure bean class is actually resolved at this point, and
// clone the bean definition in case of a dynamically resolved Class
// which cannot be stored in the shared merged bean definition.
// 取得类信息
Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {mbdToUse = new RootBeanDefinition(mbd);
mbdToUse.setBeanClass(resolvedClass);
}
// Prepare method overrides.
try {mbdToUse.prepareMethodOverrides();
}
catch (BeanDefinitionValidationException ex) {throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
beanName, "Validation of method overrides failed", ex);
}
try {
// Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
if (bean != null) {return bean;}
}
catch (Throwable ex) {throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
"BeanPostProcessor before instantiation of bean failed", ex);
}
try {
// 进入，真真正正创立 bean
Object beanInstance = doCreateBean(beanName, mbdToUse, args);
if (logger.isTraceEnabled()) {logger.trace("Finished creating instance of bean'" + beanName + "'");
}
return beanInstance;
}
catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
// A previously detected exception with proper bean creation context already,
// or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
throw ex;
}
catch (Throwable ex) {
throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
}
}
进入 doCreateBean：
/**
* Actually create the specified bean. Pre-creation processing has already happened
* at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
* <p>Differentiates between default bean instantiation, use of a
* factory method, and autowiring a constructor.
* @param beanName the name of the bean
* @param mbd the merged bean definition for the bean
* @param args explicit arguments to use for constructor or factory method invocation
* @return a new instance of the bean
* @throws BeanCreationException if the bean could not be created
* @see #instantiateBean
* @see #instantiateUsingFactoryMethod
* @see #autowireConstructor
*/
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
throws BeanCreationException {
// Instantiate the bean.
BeanWrapper instanceWrapper = null;
if (mbd.isSingleton()) {instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
}
if (instanceWrapper == null) {
// 创立 Bean 实例，仅仅调用构造方法，然而尚未设置属性
instanceWrapper = createBeanInstance(beanName, mbd, args);
}
final Object bean = instanceWrapper.getWrappedInstance();
Class<?> beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {mbd.resolvedTargetType = beanType;}
// Allow post-processors to modify the merged bean definition.
synchronized (mbd.postProcessingLock) {if (!mbd.postProcessed) {
try {applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
}
catch (Throwable ex) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Post-processing of merged bean definition failed", ex);
}
mbd.postProcessed = true;
}
}
// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
isSingletonCurrentlyInCreation(beanName));
// 放入三级缓存中
if (earlySingletonExposure) {if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean'" + beanName +
"'to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
}
// 初始化 bean 实例
Object exposedObject = bean;
try {
// Bean 属性填充
populateBean(beanName, mbd, instanceWrapper);
// 调用初始化办法，利用 BeanPostProcessor 后置处理器
exposedObject = initializeBean(beanName, exposedObject, mbd);
}
catch (Throwable ex) {if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {throw (BeanCreationException) ex;
}
else {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
}
}
if (earlySingletonExposure) {Object earlySingletonReference = getSingleton(beanName, false);
if (earlySingletonReference != null) {if (exposedObject == bean) {exposedObject = earlySingletonReference;}
else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {String[] dependentBeans = getDependentBeans(beanName);
Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
for (String dependentBean : dependentBeans) {if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {actualDependentBeans.add(dependentBean);
}
}
if (!actualDependentBeans.isEmpty()) {
throw new BeanCurrentlyInCreationException(beanName,
"Bean with name'" + beanName + "'has been injected into other beans [" +
StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
"] in its raw version as part of a circular reference, but has eventually been" +
"wrapped. This means that said other beans do not use the final version of the" +
"bean. This is often the result of over-eager type matching - consider using" +
"'getBeanNamesOfType' with the 'allowEagerInit' flag turned off, for example.");
}
}
}
}
// Register bean as disposable.
try {registerDisposableBeanIfNecessary(beanName, bean, mbd);
}
catch (BeanDefinitionValidationException ex) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
}
return exposedObject;
}
查看 populateBean 办法：
/**
* Populate the bean instance in the given BeanWrapper with the property values
* from the bean definition.
* @param beanName the name of the bean
* @param mbd the bean definition for the bean
* @param bw the BeanWrapper with bean instance
*/
@SuppressWarnings("deprecation") // for postProcessPropertyValues
protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {if (bw == null) {if (mbd.hasPropertyValues()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
}
else {
// Skip property population phase for null instance.
return;
}
}
// Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
// state of the bean before properties are set. This can be used, for example,
// to support styles of field injection.
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {return;}
}
}
}
PropertyValues pvs = (mbd.hasPropertyValues() ? mbd.getPropertyValues() : null);
int resolvedAutowireMode = mbd.getResolvedAutowireMode();
if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
// Add property values based on autowire by name if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {autowireByName(beanName, mbd, bw, newPvs);
}
// Add property values based on autowire by type if applicable.
if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {autowireByType(beanName, mbd, bw, newPvs);
}
pvs = newPvs;
}
boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);
PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {if (pvs == null) {pvs = mbd.getPropertyValues();
}
for (BeanPostProcessor bp : getBeanPostProcessors()) {if (bp instanceof InstantiationAwareBeanPostProcessor) {InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {if (filteredPds == null) {filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
if (pvsToUse == null) {return;}
}
pvs = pvsToUse;
}
}
}
if (needsDepCheck) {if (filteredPds == null) {filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
}
checkDependencies(beanName, mbd, filteredPds, pvs);
}
if (pvs != null) {applyPropertyValues(beanName, mbd, bw, pvs);
}
}
始终到 DependencyDescriptor 的 resolveCandidate 办法
resolveCandidate:276, DependencyDescriptor (org.springframework.beans.factory.config)
doResolveDependency:1391, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveDependency:1311, DefaultListableBeanFactory (org.springframework.beans.factory.support)
resolveFieldValue:656, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
inject:639, AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement (org.springframework.beans.factory.annotation)
inject:119, InjectionMetadata (org.springframework.beans.factory.annotation)
postProcessProperties:399, AutowiredAnnotationBeanPostProcessor (org.springframework.beans.factory.annotation)
populateBean:1431, AbstractAutowireCapableBeanFactory /**
* Resolve the specified bean name, as a candidate result of the matching
* algorithm for this dependency, to a bean instance from the given factory.
* <p>The default implementation calls {@link BeanFactory#getBean(String)}.
* Subclasses may provide additional arguments or other customizations.
* @param beanName the bean name, as a candidate result for this dependency
* @param requiredType the expected type of the bean (as an assertion)
* @param beanFactory the associated factory
* @return the bean instance (never {@code null})
* @throws BeansException if the bean could not be obtained
* @since 4.3.2
* @see BeanFactory#getBean(String)
*/
public Object resolveCandidate(String beanName, Class<?> requiredType, BeanFactory beanFactory)
throws BeansException {return beanFactory.getBean(beanName);
}
又调了一次 getBean 去获取援用的 bean，如果此 bean 也援用了下面的 bean 会怎么样？设第一次实例化的 bean 为 A，A 援用 B,B 同时援用 A，A 填充属性 B 的时候发现 B 没有实例化，就会去实例化 B，B 填充属性 A 的时候去缓存拿，因为 A 曾经放到三级缓存了，那么就会拿出 A，把 A 从三级缓存删除，放到二级缓存中，这样 B 就实例化好了，B 实例化好后会把本人放入以及缓存，从二级和三级缓存删除，而后回到 A 的流程，A 填充完 B，这样 A 也实例化好了。
为什么须要三级缓存，集体感觉一级其实也够用，不过一级的缓存中可能会有为填充属性的 bean，这样 spring 某些中央获取到可能有问题，那么至多要两级，一级放齐全实例化好的，二级放未填充属性的，第三级的作用是因为有些 bean 可能会须要被代理，A 援用 B，这个 B 应该是个代理类，所以须要第三级缓存来把 B 变成代理类：
if (earlySingletonExposure) {if (logger.isTraceEnabled()) {
logger.trace("Eagerly caching bean'" + beanName +
"'to allow for resolving potential circular references");
}
addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
} /**
* Obtain a reference for early access to the specified bean,
* typically for the purpose of resolving a circular reference.
* @param beanName the name of the bean (for error handling purposes)
* @param mbd the merged bean definition for the bean
* @param bean the raw bean instance
* @return the object to expose as bean reference
*/
protected Object getEarlyBeanReference(String beanName, RootBeanDefinition mbd, Object bean) {
Object exposedObject = bean;
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {exposedObject = bp.getEarlyBeanReference(exposedObject, beanName);
}
}
return exposedObject;
}