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)；
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