今天来学习下DispatcherServlet的自动配置

在我们日常的开发中除了CharacterEncodingFilter之外,DispatcherServlet 也是必不可少的一个配置。

DispatcherServlet主要用作职责调度工作，本身主要用于控制流程，主要职责如下：

1、文件上传解析，如果请求类型是multipart将通过MultipartResolver进行文件上传解析；

2、通过HandlerMapping，将请求映射到处理器（返回一个HandlerExecutionChain，它包括一个处理器、多个HandlerInterceptor拦截器）；

3、通过HandlerAdapter支持多种类型的处理器(HandlerExecutionChain中的处理器)；

4、通过ViewResolver解析逻辑视图名到具体视图实现；

5、本地化解析；

6、渲染具体的视图等；

7、如果执行过程中遇到异常将交给HandlerExceptionResolver来解析。

首先在Spring mvc框架的web.xml文件中必不可少的会有以下配置

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!-- Spring MVC servlet -->
<servlet>
    <servlet-name>SpringMVC</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:springMvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
    <async-supported>true</async-supported>
</servlet>
<servlet-mapping>
    <servlet-name>SpringMVC</servlet-name>
    <!-- 此处可以可以配置成*.do，对应struts的后缀习惯 -->
    <url-pattern>/</url-pattern>
</servlet-mapping>

在SpringBoot中则无需这样配置,框架默认有一个DispatcherServletAutoConfiguration用于完成以上功能。

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@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {

    //声明配置类 与一系列判断
	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })
	protected static class DispatcherServletConfiguration {

        //向容器中加入bean即可
		@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;
		}

	}
}

加入Ioc容器即可，如何注册Servlet可以参看另一篇文章.