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Springboot自動(dòng)裝配之注入DispatcherServlet的實(shí)現(xiàn)方法

更新時(shí)間：2022年05月20日 11:44:31 作者：萬(wàn)物皆字節(jié)

這篇文章主要介紹了Springboot自動(dòng)裝配之注入DispatcherServlet,Springboot向外界提供web服務(wù)，底層依賴了springframework中的web模塊來(lái)實(shí)現(xiàn),那么springboot在什么時(shí)機(jī)向容器注入DispatcherServlet這個(gè)核心類的呢?帶著這個(gè)問(wèn)題一起通過(guò)本文學(xué)習(xí)吧

原理概述

Springboot向外界提供web服務(wù)，底層依賴了springframework中的web模塊（包含但不限于spring mvc核心類DispatcherServlet）來(lái)實(shí)現(xiàn)

那么springboot在什么時(shí)機(jī)向容器注入DispatcherServlet這個(gè)核心類的呢
注入的流程還是遵循了自動(dòng)裝配流程，在springboot框架里默認(rèn)提供了該自動(dòng)裝配的支持

在jar包里的spring.factories文件里有個(gè) 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(gè)內(nèi)部類（配置類） DispatcherServletConfiguration、DispatcherServletRegistrationConfiguration和兩個(gè)對(duì)應(yīng)的Condition類DefaultDispatcherServletCondition、DispatcherServletRegistrationCondition

DispatcherServletConfiguration

DispatcherServletConfiguration是DispatcherServletAutoConfiguration 的一個(gè)內(nèi)部類，并被 @Configuration標(biāo)注，會(huì)被容器自動(dòng)掃描到；其有兩個(gè)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(jì)算是否要注入，主要邏輯是檢驗(yàn)Spring容器中是否已經(jīng)存在一個(gè)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(guò)在類上注解了 @Import(DispatcherServletConfiguration.class)那么這兩個(gè)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(shè)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(wù)。DispatcherServletRegistrationBean和DispatcherServlet都提供了注冊(cè)Servlet并公開(kāi)DispatcherServletPath信息的功能

面試點(diǎn)

spring mvc和spring boot的關(guān)系，相信讀了上面的文章會(huì)說(shuō)出一兩點(diǎn)；

到此這篇關(guān)于Springboot自動(dòng)裝配之注入DispatcherServlet的文章就介紹到這了,更多相關(guān)Springboot注入DispatcherServlet內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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