spring boot 2.0 源码分析（五）
在上一篇文章中我们详细分析了spring boot是如何准备上下文环境的，今天我们来看一下run函数剩余的内容。还是先把run函数贴出来：
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}我们接着往下看，来看一下this.refreshContext(context);函数，这个函数用于刷新上下文，跟踪到源码看一下：
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}在refreshContext函数中，第一行调用了refresh(context);跳转了一下，下面的代码是注册了一个应用关闭的函数钩子。
先来看refresh(context);函数：
/**
* Refresh the underlying {@link ApplicationContext}.
* @param applicationContext the application context to refresh
*/
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}通过代码跟踪分析发现，其实是调用了AbstractApplicationContext中的refresh方法。
在ServletWebServerApplicationContext和ReactiveWebServerApplicationContext的refresh函数中都是调用了super.refresh();
public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
synchronized(this.startupShutdownMonitor) {
this.prepareRefresh();
ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
this.prepareBeanFactory(beanFactory);
try {
this.postProcessBeanFactory(beanFactory);
this.invokeBeanFactoryPostProcessors(beanFactory);
this.registerBeanPostProcessors(beanFactory);
this.initMessageSource();
this.initApplicationEventMulticaster();
this.onRefresh();
this.registerListeners();
this.finishBeanFactoryInitialization(beanFactory);
this.finishRefresh();
} catch (BeansException var9) {
if(this.logger.isWarnEnabled()) {
this.logger.warn("Exception encountered during context initialization \
- cancelling refresh attempt: " + var9);
}
this.destroyBeans();
this.cancelRefresh(var9);
throw var9;
} finally {
this.resetCommonCaches();
}
}
}在这段代码中我们可以看到，其是使用了上下文中的startupShutdownMonitor属性创建一个同步代码库来执行的刷新动作。首先是实验this.prepareRefresh();准备刷新上下文：
protected void prepareRefresh() {
this.startupDate = System.currentTimeMillis();
this.closed.set(false);
this.active.set(true);
if(this.logger.isInfoEnabled()) {
this.logger.info("Refreshing " + this);
}
this.initPropertySources();
this.getEnvironment().validateRequiredProperties();
this.earlyApplicationEvents = new LinkedHashSet();
}接着获取了bean工厂以后，设置了一些bean工厂的环境：
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
beanFactory.setBeanClassLoader(this.getClassLoader());
beanFactory.setBeanExpressionResolver(
new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(
new ResourceEditorRegistrar(this, this.getEnvironment()));
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.registerResolvableDependency(BeanFactory.class, beanFactory);
beanFactory.registerResolvableDependency(ResourceLoader.class, this);
beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);
beanFactory.registerResolvableDependency(ApplicationContext.class, this);
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(this));
if(beanFactory.containsBean("loadTimeWeaver")) {
beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
beanFactory.setTempClassLoader(
new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
}
if(!beanFactory.containsLocalBean("environment")) {
beanFactory.registerSingleton("environment", this.getEnvironment());
}
if(!beanFactory.containsLocalBean("systemProperties")) {
beanFactory.registerSingleton("systemProperties",
this.getEnvironment().getSystemProperties());
}
if(!beanFactory.containsLocalBean("systemEnvironment")) {
beanFactory.registerSingleton("systemEnvironment",
this.getEnvironment().getSystemEnvironment());
}
}接下来是发送了一个bean工厂的处理信号，其中ServletWebServerApplicationContext中的实现是在bean工厂里添加了一个WebApplicationContextServletContextAwareProcessor处理器：
protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
beanFactory.addBeanPostProcessor(
new WebApplicationContextServletContextAwareProcessor(this));
beanFactory.ignoreDependencyInterface(ServletContextAware.class);
}紧接着就是调用了这处理器，并且注册到bean工厂。然后就是分别调用了initMessageSource()和initApplicationEventMulticaster()用于初始化监听器和监听管理器：
protected void initMessageSource() {
ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
if(beanFactory.containsLocalBean("messageSource")) {
this.messageSource = (MessageSource)beanFactory
.getBean("messageSource", MessageSource.class);
if(this.parent != null && this.messageSource instanceof HierarchicalMessageSource) {
HierarchicalMessageSource dms = (HierarchicalMessageSource)this.messageSource;
if(dms.getParentMessageSource() == null) {
dms.setParentMessageSource(this.getInternalParentMessageSource());
}
}
if(this.logger.isDebugEnabled()) {
this.logger.debug("Using MessageSource [" + this.messageSource + "]");
}
} else {
DelegatingMessageSource dms1 = new DelegatingMessageSource();
dms1.setParentMessageSource(this.getInternalParentMessageSource());
this.messageSource = dms1;
beanFactory.registerSingleton("messageSource", this.messageSource);
if(this.logger.isDebugEnabled()) {
this.logger.debug("Unable to locate MessageSource with name
\'messageSource\': using default [" + this.messageSource + "]");
}
}
}
protected void initApplicationEventMulticaster() {
ConfigurableListableBeanFactory beanFactory = this.getBeanFactory();
if(beanFactory.containsLocalBean("applicationEventMulticaster")) {
this.applicationEventMulticaster = (ApplicationEventMulticaster)beanFactory
.getBean("applicationEventMulticaster", ApplicationEventMulticaster.class);
if(this.logger.isDebugEnabled()) {
this.logger.debug("Using ApplicationEventMulticaster [" +
this.applicationEventMulticaster + "]");
}
} else {
this.applicationEventMulticaster = new SimpleApplicationEventMulticaster(beanFactory);
beanFactory.registerSingleton("applicationEventMulticaster",
this.applicationEventMulticaster);
if(this.logger.isDebugEnabled()) {
this.logger.debug("Unable to locate ApplicationEventMulticaster with name
\'applicationEventMulticaster\':
using default [" + this.applicationEventMulticaster + "]");
}
}
}在initMessageSource函数中会首先判断beanFactory工厂中是否已经存在messageSource，如果不存在就会为当前的messageSource创建一个新的DelegatingMessageSource。
initApplicationEventMulticaster的初始化方式跟initMessageSource差不多，这里不再多述。
继续看run函数，接下来调用onRefresh()函数，这个函数只是发送一个刷新的事件，源码中并没有具体的实现。
接着放下看，this.registerListeners();把spring容器内的listener和beanfactory的listener都添加到广播器中：
protected void registerListeners() {
Iterator listenerBeanNames = this.getApplicationListeners().iterator();
while(listenerBeanNames.hasNext()) {
ApplicationListener earlyEventsToProcess = (ApplicationListener)listenerBeanNames.next();
this.getApplicationEventMulticaster().addApplicationListener(earlyEventsToProcess);
}
String[] var6 = this.getBeanNamesForType(ApplicationListener.class, true, false);
String[] var7 = var6;
int var3 = var6.length;
for(int earlyEvent = 0; earlyEvent < var3; ++earlyEvent) {
String listenerBeanName = var7[earlyEvent];
this.getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);
}
Set var8 = this.earlyApplicationEvents;
this.earlyApplicationEvents = null;
if(var8 != null) {
Iterator var9 = var8.iterator();
while(var9.hasNext()) {
ApplicationEvent var10 = (ApplicationEvent)var9.next();
this.getApplicationEventMulticaster().multicastEvent(var10);
}
}
}通过this.finishBeanFactoryInitialization(beanFactory);实例化BeanFactory 中已经被注册但是没被实例化的所有实例。初始化的过程中各种BeanPostProcessor就开始生效了：
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
if(beanFactory.containsBean("conversionService") &&
beanFactory.isTypeMatch("conversionService", ConversionService.class)) {
beanFactory.setConversionService((ConversionService)beanFactory
.getBean("conversionService", ConversionService.class));
}
if(!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver((strVal) -> {
return this.getEnvironment().resolvePlaceholders(strVal);
});
}
String[] weaverAwareNames = beanFactory
.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
String[] var3 = weaverAwareNames;
int var4 = weaverAwareNames.length;
for(int var5 = 0; var5 < var4; ++var5) {
String weaverAwareName = var3[var5];
this.getBean(weaverAwareName);
}
beanFactory.setTempClassLoader((ClassLoader)null);
beanFactory.freezeConfiguration();
beanFactory.preInstantiateSingletons();
}接下来调用finishRefresh()函数用于完成刷新后的一些扫尾工作，包括产生的缓存、初始化生命周期处理器LifecycleProcessor，并调用其onRefresh()方法、发布事件、调用LiveBeansView的registerApplicationContext注册context。
protected void finishRefresh() {
this.clearResourceCaches();
this.initLifecycleProcessor();
this.getLifecycleProcessor().onRefresh();
this.publishEvent((ApplicationEvent)(new ContextRefreshedEvent(this)));
LiveBeansView.registerApplicationContext(this);
}接着看run函数，在刷新完context后，调用了一个afterRefresh函数，这个函数前面已经说过了，是为了给ApplicationContext的子类留下的一个扩展点。
然后调用了listeners.started(context);，把监听器设置成了已经启动的状态。
最后调用了callRunners函数，获取所有的ApplicationRunner和CommandLineRunner然后调用他们的run方法：
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<>();
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
AnnotationAwareOrderComparator.sort(runners);
for (Object runner : new LinkedHashSet<>(runners)) {
if (runner instanceof ApplicationRunner) {
callRunner((ApplicationRunner) runner, args);
}
if (runner instanceof CommandLineRunner) {
callRunner((CommandLineRunner) runner, args);
}
}
}总结：spring boot 2.0在启动的时候，首先会调用SpringApplication的构造函数进行初始化，调用实例函数run，在run函数中，首先获取监听器，并设置成启动状态，后面准备环境prepareEnvironment，准备prepareContext上下文，刷新上下文refreshContext，最后调用callRunners来依次调用注册的Runner。
