Apakah proses permulaan WEB dalam SpringBoot?

Saya percaya semua orang telah mengalami kemudahan springboot Pada masa lalu, jika kami ingin menjalankan projek web, kami perlu membungkus projek itu ke dalam pakej perang, dan kemudian menjalankan Tomcat untuk memulakan projek itu kami mempunyai springboot, kami boleh memulakannya semudah pakej jar Untuk memulakan projek web, hari ini kami akan menganalisis keseluruhan proses memulakan projek web dengan springboot.

Seperti biasa, kita mulakan dengan fail spring.factories.

Tiada fail spring.factories di bawah spring-boot-starter-web

Oleh itu, kita boleh menggunakan spring.factories file dalam spring-boot- autoconfigure Start

1. Pendaftaran DispatcherServlet

1.1 Suntikan DispatcherServlet ke dalam bekas IOC

DispatcherServlet didaftarkan melalui DispatcherServlet

Ini juga sebab bekas IOC dan bekas WEB dalam SpringBoot adalah sama

Selepas Spring meletakkan DispatcherServlet ke dalam bekas, kaedah postProcessBeforeInitialization ApplicationContextAwareProcessor akan dilaksanakan semasa pemulaan DispatcherServlet, dan Lapisan bawah postProcessBeforeInitialization adalah seperti berikut

@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");
		}

	}

}

dan DispatcherServlet ialah ApplicationContextAware, jadi ia akan melaksanakan kaedah setApplicationContext dan menetapkan sifatnya webApplicationContext

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);
		}
	}

semasa proses permulaan kontena web, bekas web akan ditetapkan sama dengan bekas ioc Begitu juga, kod penciptaan kontena springMVC adalah seperti berikut, rujuk artikel springMVC permulaan beranotasi sepenuhnya dan permulaan kontena

@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;
		}
	}

.

Seseorang mungkin bertanya di sini, mengapa dalam persekitaran springMVC, this.webApplicationContext adalah batal, kerana tiada DispatcherServlet dalam SpringMVC Management melalui bekas spring

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;
	}

1.2 Suntikan DispatcherServlet ke dalam bekas Servlet

Bekas dalam SpringBoot ialah AnnotationConfigServletWebServerApplicationContext, dan kaedah onRefresh()nya adalah seperti berikut

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);
	}

Perhatikan bahawa dia tidak SpringServletContainerInitializer akan dilaksanakan.

Prosesnya adalah seperti berikut

1. Laksanakan semua ServletContextInitializers dalam bekas melalui kaedah getSelfInitializer()

@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();
	}

ServletContextInitializer mempunyai subkelas ServletRegistration, yang dimasukkan ke dalamServletRegistration. Bekas Servlet melalui kaedah addRegistration

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);
	}
}

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