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# run(String... args)解析
**run函数**
```java
/**
* Run the Spring application, creating and refreshing a new ApplicationContext
*/
public ConfigurableApplicationContext run(String... args) {
//计时器
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
//设置java.awt.headless系统属性为true，Headless模式是系统的一种配置模式。
// 在该模式下，系统缺少了显示设备、键盘或鼠标。但是服务器生成的数据需要提供给显示设备等使用。
// 因此使用headless模式，一般是在程序开始激活headless模式，告诉程序，现在你要工作在Headless mode下，依靠系统的计算能力模拟出这些特性来
configureHeadlessProperty();
//获取监听器集合对象
SpringApplicationRunListeners listeners = getRunListeners(args);
//发出开始执行的事件。
listeners.starting();
try {
//根据main函数传入的参数，创建DefaultApplicationArguments对象
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//根据扫描到的监听器对象和函数传入参数，进行环境准备。
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
//和上面套路一样，读取spring.factories文件
//key 是 SpringBootExceptionReporter 对应的value
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//和上面的一样，context准备完成之后，将触发SpringApplicationRunListener的contextPrepared执行
refreshContext(context);
//其实啥也没干。但是老版本的callRunners好像是在这里执行的。
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
//发布ApplicationStartedEvent事件，发出结束执行的事件
listeners.started(context);
//在某些情况下，我们希望在容器bean加载完成后执行一些操作，会实现ApplicationRunner或者CommandLineRunner接口
//后置操作，就是在容器完成刷新后，依次调用注册的Runners，还可以通过@Order注解设置各runner的执行顺序。
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;
}
```
## **1.获取run listeners**
```java
SpringApplicationRunListeners listeners = getRunListeners(args);
```
和构造器设置初始化器一个套路，根据传入type SpringApplicationRunListener去扫描spring.factories文件，读取type对应的value并实例化。然后利用实例化对象创建SpringApplicationRunListeners对象。
```java
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener
```
EventPublishingRunListener的作用是发布SpringApplicationEvent事件。
* 内部有一个 SimpleApplicationEventMulticaster
```java
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
...
```
## **2.发出开始执行的事件**
```java
listeners.starting();
```
继续跟进starting函数，
```java
public void starting() {
this.initialMulticaster.multicastEvent(
new ApplicationStartingEvent(this.application, this.args));
}
```
SimpleApplicationEventMulticaster.multicastEvent
```java
//获取ApplicationStartingEvent类型的事件后，发布事件
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
Executor executor = getTaskExecutor();
if (executor != null) {
executor.execute(() -> invokeListener(listener, event));
}
else {
invokeListener(listener, event);
}
}
}
//继续跟进invokeListener方法,最后调用ApplicationListener监听者的onApplicationEvent处理事件
private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
try {
listener.onApplicationEvent(event);
}
catch (ClassCastException ex) {
.....
}
}
```
这个后面也会反复遇到，比如listeners.running(context)。
这里是典型的观察者模式。
```java
//观察者：监听<E extends ApplicationEvent>类型事件
ApplicationListener<E extends ApplicationEvent> extends EventListener
//事件类型：
Event extends SpringApplicationEvent extends ApplicationEvent extends EventObject
//被观察者：发布事件
EventPublishingRunListener implements SpringApplicationRunListener
```
SpringApplication根据当前事件Event类型，比如ApplicationStartingEvent，查找到监听ApplicationStartingEvent的观察者EventPublishingRunListener，调用观察者的onApplicationEvent处理事件。
## **3.环境准备**
```java
//根据main函数传入的参数，创建DefaultApplicationArguments对象
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//根据扫描到的listeners对象和函数传入参数，进行环境准备。
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
```
ApplicationArguments提供运行application的参数，后面会作为一个Bean注入到容器。这里重点说下prepareEnvironment方法做了些什么。
```java
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
//和listeners.starting一样的流程
listeners.environmentPrepared(environment);
//上述完成了环境的创建和配置，传入的参数和资源加载到environment
//绑定环境到SpringApplication
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
```
这段代码核心有3个。
1. configureEnvironment，用于基本运行环境的配置。
2. 发布事件ApplicationEnvironmentPreparedEvent。和发布ApplicationStartingEvent事件的流程一样。
3. 绑定环境到SpringApplication
## **4.创建ApplicationContext**
```java
context = createApplicationContext();
```
传说中的IOC容器终于来了。
在实例化context之前，首先需要确定context的类型，这个是根据应用类型确定的。应用类型webApplicationType在构造器已经推断出来了。
```java
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
//应用为servlet类型的web应用
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
//应用为响应式web应用
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
//应用为非web类型的应用
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
```
获取context类型后，进行实例化，这里根据class类型获取无参构造器进行实例化。
```java
public static <T> T instantiateClass(Class<T> clazz) throws BeanInstantiationException {
Assert.notNull(clazz, "Class must not be null");
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
//clazz.getDeclaredConstructor()获取无参的构造器，然后进行实例化
return instantiateClass(clazz.getDeclaredConstructor());
}
catch (NoSuchMethodException ex) {
.......
}
```
比如web类型为servlet类型，就会实例化org.springframework.boot.web.servlet.context.
AnnotationConfigServletWebServerApplicationContext类型的context。
## **5.context前置处理阶段**
```java
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
//关联环境
context.setEnvironment(environment);
//ApplicationContext预处理，主要配置Bean生成器以及资源加载器
postProcessApplicationContext(context);
//调用初始化器，执行initialize方法，前面set的初始化器终于用上了
applyInitializers(context);
//发布contextPrepared事件，和发布starting事件一样，不多说
listeners.contextPrepared(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
//bean, springApplicationArguments,用于获取启动application所需的参数
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
//加载打印Banner的Bean
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// Load the sources，根据primarySources加载resource。
// primarySources:一般为主类的class对象
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
//构造BeanDefinitionLoader并完成定义的Bean的加载
load(context, sources.toArray(new Object[0]));
//发布ApplicationPreparedEvent事件，表示application已准备完成
listeners.contextLoaded(context);
}
```
## **6.刷新容器**
```java
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);
// 注册一个关闭容器时的钩子函数,在jvm关闭时调用
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}
```
调用父类AbstractApplicationContext刷新容器的操作
```java
@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();
}
......
}
```
## **7.后置操作，调用Runners**
后置操作，就是在容器完成刷新后，依次调用注册的Runners，还可以通过@Order注解设置各runner的执行顺序。
Runner可以通过实现ApplicationRunner或者CommandLineRunner接口。
```java
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);
}
}
}
```
根据源码可知，runners收集从容器获取的ApplicationRunner和CommandLineRunner类型的Bean，然后依次执行。
## **8.发布ApplicationReadyEvent事件**
```java
listeners.running(context);
```
应用启动完成，可以对外提供服务了，在这里发布ApplicationReadyEvent事件。流程还是和starting时一样。