Springboot自动装配之注入DispatcherServlet怎么实现

这篇文章主要介绍“Springboot自动装配之注入DispatcherServlet怎么实现”，在日常操作中，相信很多人在Springboot自动装配之注入DispatcherServlet怎么实现问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”Springboot自动装配之注入DispatcherServlet怎么实现”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

原理概述

Springboot向外界提供web服务，底层依赖了springframework中的web模块（包含但不限于spring mvc核心类DispatcherServlet）来实现

那么springboot在什么时机向容器注入DispatcherServlet这个核心类的呢
注入的流程还是遵循了自动装配流程，在springboot框架里默认提供了该自动装配的支持

在jar包里的spring.factories文件里有个 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 {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";// ... 省略代码}

在DispatcherServletAutoConfiguration中有两个内部类（配置类） DispatcherServletConfiguration、DispatcherServletRegistrationConfiguration和两个对应的Condition类DefaultDispatcherServletCondition、DispatcherServletRegistrationCondition

DispatcherServletConfiguration

DispatcherServletConfiguration是DispatcherServletAutoConfiguration 的一个内部类，并被 @Configuration标注，会被容器自动扫描到；其有两个方法： 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 incorrectlyreturn resolver;}}

@A：

• @Configuration(proxyBeanMethods = false)：配置类采用Lite模式

• @Conditional(DefaultDispatcherServletCondition.class)：根据DefaultDispatcherServletCondition类返回值计算是否要注入，主要逻辑是检验Spring容器中是否已经存在一个名字为"dispatcherServlet"的DispatcherServlet

• @ConditionalOnClass(ServletRegistration.class)：容器中必须要有ServletRegistration类

• @EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })：加载HttpProperties和WebMvcProperties

@B：注入 MultipartResolver 解析类

DispatcherServletRegistrationConfiguration

该类注入的逻辑与DispatcherServletConfiguration 相同，只不过在类上注解了 @Import(DispatcherServletConfiguration.class)那么这两个类定义就有了先后顺序

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

其中，DispatcherServletRegistrationBean继承自ServletRegistrationBean，主要为DispatcherServlet提供服务。DispatcherServletRegistrationBean和DispatcherServlet都提供了注册Servlet并公开DispatcherServletPath信息的功能

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