Springboot自動裝配之注入DispatcherServlet的實現(xiàn)方法

更新時間：2022年05月20日 11:44:31 作者：萬物皆字節(jié)

這篇文章主要介紹了Springboot自動裝配之注入DispatcherServlet,Springboot向外界提供web服務，底層依賴了springframework中的web模塊來實現(xiàn),那么springboot在什么時機向容器注入DispatcherServlet這個核心類的呢?帶著這個問題一起通過本文學習吧

原理概述

Springboot向外界提供web服務，底層依賴了springframework中的web模塊（包含但不限于spring mvc核心類DispatcherServlet）來實現(xiàn)

那么springboot在什么時機向容器注入DispatcherServlet這個核心類的呢
注入的流程還是遵循了自動裝配流程，在springboot框架里默認提供了該自動裝配的支持

在jar包里的spring.factories文件里有個 org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration配置

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
	/*
	 * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
	/*
	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
	 *
	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";
	// ... 省略代碼
	}

在DispatcherServletAutoConfiguration中有兩個內(nèi)部類（配置類） DispatcherServletConfiguration、DispatcherServletRegistrationConfiguration和兩個對應的Condition類DefaultDispatcherServletCondition、DispatcherServletRegistrationCondition

DispatcherServletConfiguration

DispatcherServletConfiguration是DispatcherServletAutoConfiguration 的一個內(nèi)部類，并被 @Configuration標注，會被容器自動掃描到；其有兩個方法： 1、dispatcherServlet；2、multipartResolver

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

// @A
		@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;
		}

// @B
		@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;
		}
	}

@A：

@Configuration(proxyBeanMethods = false)：配置類采用Lite模式
@Conditional(DefaultDispatcherServletCondition.class)：根據(jù)DefaultDispatcherServletCondition類返回值計算是否要注入，主要邏輯是檢驗Spring容器中是否已經(jīng)存在一個名字為"dispatcherServlet"的DispatcherServlet
@ConditionalOnClass(ServletRegistration.class)：容器中必須要有ServletRegistration類
@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })：加載HttpProperties和WebMvcProperties

@B：注入 MultipartResolver 解析類

DispatcherServletRegistrationConfiguration

該類注入的邏輯與DispatcherServletConfiguration 相同，只不過在類上注解了 @Import(DispatcherServletConfiguration.class)那么這兩個類定義就有了先后順序

@Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class) //@A
	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());
			// 設置名稱		
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}
	}

其中，DispatcherServletRegistrationBean繼承自ServletRegistrationBean，主要為DispatcherServlet提供服務。DispatcherServletRegistrationBean和DispatcherServlet都提供了注冊Servlet并公開DispatcherServletPath信息的功能