前言

当Servlet接管到申请后会最终调用doDispatch办法后会去找到对应的HandlerMapping，同时也会找到配置的拦截器，最终组成须要的HandlerExecutionChain执行链（这里省略局部代码保留次要性能）：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {                // 1.确定应用的handler                HandlerExecutionChain mappedHandler = getHandler(processedRequest);                if (mappedHandler == null) {                    noHandlerFound(processedRequest, response);                    return;                }                // 确定handler的适配器                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());                // 拦截器前置调用                if (!mappedHandler.applyPreHandle(processedRequest, response)) {                    return;                }                // 理论调用                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());                // 设置默认视图名                applyDefaultViewName(processedRequest, mv);                // 拦截器后置调用                mappedHandler.applyPostHandle(processedRequest, response, mv);            // 散发后果            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);    }

拦截器

在开发中拦截器的应用是比拟频繁的，例如用户拦截器，权限拦截器等。sringmvc的拦截器提供了pre,post,after三种期间的办法（调用处理器办法前，调用后，返回数据后），十分不便的进行资源设置，开释等性能。

public interface HandlerInterceptor {    // 前    default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)            throws Exception {        return true;    }    // 中    default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,            @Nullable ModelAndView modelAndView) throws Exception {    }    // 后    default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,            @Nullable Exception ex) throws Exception {    }}

拦截器注册

当初看看拦截器是怎么注册的？spring提供两种形式。

1. 配置类注册EnableWebMvcConfiguration#setConfigurers通常在开发中咱们会应用本人编写实现WebMvcConfigurer接口的形式增加拦截器，并把注册类注册到IOC容器中，EnableWebMvcConfiguration#setConfigurers就会应用@Autowired进行制动注入。```java@Autowired(required = false)public void setConfigurers(List<WebMvcConfigurer> configurers) {    if (!CollectionUtils.isEmpty(configurers)) {        this.configurers.addWebMvcConfigurers(configurers);    }}```最初把注册的拦截器注册到HandlerMapping当中去,（以RequestMappingHandlerMapping为例）代码如下，getInterceptors办法最终会调用所有WebMvcConfigurer实例增加拦截器的办法，从而将咱们自定义的拦截器注册到HanderMapping当中去```javapublic RequestMappingHandlerMapping requestMappingHandlerMapping(            @Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,            @Qualifier("mvcConversionService") FormattingConversionService conversionService,            @Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {        RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();        mapping.setOrder(0);        mapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));        ……```2. 以MappedInterceptor类实例或者子类间接注册到IOC容器中因为HandlerMapping继承WebApplicationObjectSupport，再创立bean的时候会调用其initApplicationContext办法。而该办法会注册容器中的MappedInterceptor类的bean。    这样咱们就能够应用这些拦截器了。

总结

最初以一个流程图直观总结一下其过程：