SpringBoot中WEB的启动流程分析

更新时间：2022年03月30日 12:02:02 作者：这是一条海鱼

今天我们就来分析下springboot启动web项目整个流程，本文通过实例代码给大家介绍的非常详细，对大家的学习或工作具有一定的参考借鉴价值，需要的朋友参考下吧

想必大家都体验过springboot的便捷，以前想要运行web项目，我们首先需要将项目打成war包，然后再运行Tomcat启动项目，不过自从有了springboot，我们可以像启动jar包一样简单的启动一个web项目，今天我们就来分析下springboot启动web项目整个流程。

老规矩，我们从spring.factories文件开始。

spring-boot-starter-web下没有spring.factories文件

在这里插入图片描述

所以我们从spring-boot-autoconfigure下的spring.factories开始

在这里插入图片描述

一、DispatcherServlet的注册

1.1 把DispatcherServlet注入IOC容器

DispatcherServlet是通过DispatcherServletAutoConfiguration注册的

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {

	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";

	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";

	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })
	protected static class DispatcherServletConfiguration {

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServlet dispatcherServlet(HttpProperties httpProperties, WebMvcProperties webMvcProperties) {
			DispatcherServlet dispatcherServlet = new DispatcherServlet();
			dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
			dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
			dispatcherServlet.setEnableLoggingRequestDetails(httpProperties.isLogRequestDetails());
			return dispatcherServlet;
		}

		@Bean
		@ConditionalOnBean(MultipartResolver.class)
		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
		public MultipartResolver multipartResolver(MultipartResolver resolver) {
			// Detect if the user has created a MultipartResolver but named it incorrectly
			return resolver;
		}

	}

	@Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class)
	protected static class DispatcherServletRegistrationConfiguration {

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
		@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
				WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
			DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					webMvcProperties.getServlet().getPath());
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup()); 
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}

	}

	@Order(Ordered.LOWEST_PRECEDENCE - 10)
	private static class DefaultDispatcherServletCondition extends SpringBootCondition {

		@Override
		public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
			ConditionMessage.Builder message = ConditionMessage.forCondition("Default DispatcherServlet");
			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
			List<String> dispatchServletBeans = Arrays
					.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
			if (dispatchServletBeans.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome
						.noMatch(message.found("dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			if (beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome.noMatch(
						message.found("non dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			if (dispatchServletBeans.isEmpty()) {
				return ConditionOutcome.match(message.didNotFind("dispatcher servlet beans").atAll());
			}
			return ConditionOutcome.match(message.found("dispatcher servlet bean", "dispatcher servlet beans")
					.items(Style.QUOTE, dispatchServletBeans)
					.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
		}

	}

	@Order(Ordered.LOWEST_PRECEDENCE - 10)
	private static class DispatcherServletRegistrationCondition extends SpringBootCondition {

		@Override
		public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
			ConditionOutcome outcome = checkDefaultDispatcherName(beanFactory);
			if (!outcome.isMatch()) {
				return outcome;
			}
			return checkServletRegistration(beanFactory);
		}

		private ConditionOutcome checkDefaultDispatcherName(ConfigurableListableBeanFactory beanFactory) {
			List<String> servlets = Arrays
					.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
			boolean containsDispatcherBean = beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			if (containsDispatcherBean && !servlets.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome.noMatch(
						startMessage().found("non dispatcher servlet").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			return ConditionOutcome.match();
		}

		private ConditionOutcome checkServletRegistration(ConfigurableListableBeanFactory beanFactory) {
			ConditionMessage.Builder message = startMessage();
			List<String> registrations = Arrays
					.asList(beanFactory.getBeanNamesForType(ServletRegistrationBean.class, false, false));
			boolean containsDispatcherRegistrationBean = beanFactory
					.containsBean(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
			if (registrations.isEmpty()) {
				if (containsDispatcherRegistrationBean) {
					return ConditionOutcome.noMatch(message.found("non servlet registration bean")
							.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
				}
				return ConditionOutcome.match(message.didNotFind("servlet registration bean").atAll());
			}
			if (registrations.contains(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)) {
				return ConditionOutcome.noMatch(message.found("servlet registration bean")
						.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
			}
			if (containsDispatcherRegistrationBean) {
				return ConditionOutcome.noMatch(message.found("non servlet registration bean")
						.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
			}
			return ConditionOutcome.match(message.found("servlet registration beans").items(Style.QUOTE, registrations)
					.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
		}

		private ConditionMessage.Builder startMessage() {
			return ConditionMessage.forCondition("DispatcherServlet Registration");
		}

	}

}

这也是SpringBoot中IOC容器和WEB容器是同一个的原因

Spring把DispatcherServlet放到容器中后，在DispatcherServlet的初始化中会执行ApplicationContextAwareProcessor的postProcessBeforeInitialization方法，而其postProcessBeforeInitialization底层如下

private void invokeAwareInterfaces(Object bean) {
		if (bean instanceof EnvironmentAware) {
			((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
		}
		if (bean instanceof EmbeddedValueResolverAware) {
			((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
		}
		if (bean instanceof ResourceLoaderAware) {
			((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
		}
		if (bean instanceof ApplicationEventPublisherAware) {
			((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
		}
		if (bean instanceof MessageSourceAware) {
			((MessageSourceAware) bean).setMessageSource(this.applicationContext);
		}
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}

而DispatcherServlet是一个ApplicationContextAware，所以会执行其setApplicationContext方法，设置其属性webApplicationContext

@Override
	public void setApplicationContext(ApplicationContext applicationContext) {
	   //传入ioc容器
		if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {
			this.webApplicationContext = (WebApplicationContext) applicationContext;
			this.webApplicationContextInjected = true;
		}
	}

所以在web容器启动过程会把web容器设置成和ioc容器一样，springMVC容器创建代码如下，参考文章springMVC全注解启动和容器的初始化

protected WebApplicationContext initWebApplicationContext() {
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;
        //因为webApplicationContext这里有值了，所以会进入这里
		if (this.webApplicationContext != null) {
	        //把web容器设置成和ioc容器一样
			wac = this.webApplicationContext;
			if (wac instanceof ConfigurableWebApplicationContext) {
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
				if (!cwac.isActive()) {
					if (cwac.getParent() == null) 
						cwac.setParent(rootContext);
					}
					configureAndRefreshWebApplicationContext(cwac);
				}
			}
		}
		if (wac == null) {
			wac = findWebApplicationContext();
			wac = createWebApplicationContext(rootContext);
		if (!this.refreshEventReceived) {
			synchronized (this.onRefreshMonitor) {
				onRefresh(wac);
		if (this.publishContext) {
			String attrName = getServletContextAttributeName();
			getServletContext().setAttribute(attrName, wac);
		return wac;
	}

这里可能要有人问了，为什么在springMVC环境中，this.webApplicationContext为null,因为在springMVC中DispatcherServlet没有通过spring容器管理

protected void registerDispatcherServlet(ServletContext servletContext) {
		String servletName = getServletName();
		Assert.hasLength(servletName, "getServletName() must not return null or empty");
        //创建web容器
		WebApplicationContext servletAppContext = createServletApplicationContext();
		Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");
        //创建DispatcherServlet对象
		FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
		Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
		dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
        //把dispatcherServlet作为Servlet注册到上下文中
		ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
		if (registration == null) {
			throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
					"Check if there is another servlet registered under the same name.");
		}
        //容器在启动的时候加载这个servlet，其优先级为1（正数的值越小，该servlet的优先级越高，应用启动时就越先加载）
		registration.setLoadOnStartup(1);
		//设置Servlet映射mapping路径
		//getServletMappings()是模版方法，需要我们自己配置
		registration.addMapping(getServletMappings());
		//设置是否支持异步请求
		//isAsyncSupported默认是true
		registration.setAsyncSupported(isAsyncSupported());
        //处理自定义的Filter进来，一般我们Filter不这么加进来，而是自己@WebFilter，或者借助Spring，  
        //备注：这里添加进来的Filter都仅仅只拦截过滤上面注册的dispatchServlet
		Filter[] filters = getServletFilters();
		if (!ObjectUtils.isEmpty(filters)) {
			for (Filter filter : filters) {
				registerServletFilter(servletContext, filter);
			}
		}
		//这个很清楚：调用者若相对dispatcherServlet有自己更个性化的参数设置，复写此方法即可
		customizeRegistration(registration);
	}

1.2 把DispatcherServlet注入Servlet容器

SpringBoot中容器是AnnotationConfigServletWebServerApplicationContext，其onRefresh()方法如下

@Override
protected void onRefresh() {
	super.onRefresh();
	try {
		createWebServer(); //创建Servlet容器
	}
	catch (Throwable ex) {
		throw new ApplicationContextException("Unable to start web server", ex);
	}
}

private void createWebServer() {
		WebServer webServer = this.webServer;
		ServletContext servletContext = getServletContext();
		if (webServer == null && servletContext == null) {
			ServletWebServerFactory factory = getWebServerFactory(); 
			this.webServer = factory.getWebServer(getSelfInitializer());//创建容器，并执行所有ServletContextInitializer的onStartup
		}
		else if (servletContext != null) {
			try {
				getSelfInitializer().onStartup(servletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context", ex);
			}
		}
		initPropertySources();
	}

注意，这里他不会执行SpringServletContainerInitializer。

流程如下
1、通过getSelfInitializer()方法执行容器中所有的ServletContextInitializer

private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
	return this::selfInitialize;
}
private void selfInitialize(ServletContext servletContext) throws ServletException {
	prepareWebApplicationContext(servletContext);
	registerApplicationScope(servletContext);
	WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
	for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
		beans.onStartup(servletContext);
	}
}

而ServletContextInitializer有个子类ServletRegistrationBean，通过其addRegistration方法注入Servlet容器中

@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
	String name = getServletName();
	return servletContext.addServlet(name, this.servlet);
}

到此这篇关于SpringBoot中WEB的启动的文章就介绍到这了,更多相关SpringBoot WEB启动内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家！

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