自定义类拦截器

在讲拦截器前先说说SpringMVC的流程

用户发送请求至前端控制器（DispatcherServlet） 提示：DispatcherServlet的作用：接受请求，调用其他组件处理请求，响应结果，相当于转发器，中央处理器，是整个流程的控制中心。

前端控制器（DispatcherServlet）收到请求后调用处理器映射器（HandlerMapping） 处理器映射器(HandlerMapping)找到具体的Controller(可以根据xml配置、注解进行查找)，并将Controller返回给DispatcherServlet；

前端控制器(DispatcherServlet)调用处理器适配器(HandlerAdapter)。处理器适配器经过适配调用具体的Controller；(Controller–> service --> Dao --> 数据库)Controller执行完成后返回ModelAndView 提示：Model(模型数据，即Controller处理的结果，Map) View(逻辑视图名，即负责展示结果的JSP页面的名字) 处理器适配器(HandlerAdapter)将controller执行的结果(ModelAndView)返回给前端控制器(DispatcherServlet)；

前端控制器(DispatcherServlet)将执行的结果(ModelAndView)传给视图解析器(ViewReslover) 视图解析器(ViewReslover)根据View(逻辑视图名)解析后返回具体JSP页面

前端控制器(DispatcherServlet)根据Model对View进行渲染（即将模型数据填充至视图中）； 前端控制器(DispatcherServlet)将填充了数据的网页响应给用户。

拦截器配置

web.xml 需要在web.xml中添加拦截器标签拦截器配置 1.定义拦截器类 2.配置拦截器的配置文件

自定义拦截器类实现HandlerInterceptor

根据业务需求实现当中的方法

HandlerInterceptor接口的源码

public interface HandlerInterceptor { /** * Intercept the execution of a handler. Called after HandlerMapping determined * an appropriate handler object, but before HandlerAdapter invokes the handler. * <p>DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can decide to abort the execution chain, * typically sending a HTTP error or writing a custom response. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * <p>The default implementation returns {@code true}. * @param request current HTTP request * @param response current HTTP response * @param handler chosen handler to execute, for type and/or instance evaluation * @return {@code true} if the execution chain should proceed with the * next interceptor or the handler itself. Else, DispatcherServlet assumes * that this interceptor has already dealt with the response itself. * @throws Exception in case of errors */ default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { return true; } /** * Intercept the execution of a handler. Called after HandlerAdapter actually * invoked the handler, but before the DispatcherServlet renders the view. * Can expose additional model objects to the view via the given ModelAndView. * <p>DispatcherServlet processes a handler in an execution chain, consisting * of any number of interceptors, with the handler itself at the end. * With this method, each interceptor can post-process an execution, * getting applied in inverse order of the execution chain. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * <p>The default implementation is empty. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param modelAndView the {@code ModelAndView} that the handler returned * (can also be {@code null}) * @throws Exception in case of errors */ default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable ModelAndView modelAndView) throws Exception { } /** * Callback after completion of request processing, that is, after rendering * the view. Will be called on any outcome of handler execution, thus allows * for proper resource cleanup. * <p>Note: Will only be called if this interceptor's {@code preHandle} * method has successfully completed and returned {@code true}! * <p>As with the {@code postHandle} method, the method will be invoked on each * interceptor in the chain in reverse order, so the first interceptor will be * the last to be invoked. * <p><strong>Note:</strong> special considerations apply for asynchronous * request processing. For more details see * {@link org.springframework.web.servlet.AsyncHandlerInterceptor}. * <p>The default implementation is empty. * @param request current HTTP request * @param response current HTTP response * @param handler handler (or {@link HandlerMethod}) that started asynchronous * execution, for type and/or instance examination * @param ex exception thrown on handler execution, if any * @throws Exception in case of errors */ default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, @Nullable Exception ex) throws Exception { } }

HandlerInterceptor中的三个方法

PreHandler方法：在请求发出后，在没有到达业务层前就进行拦截postHandle方法：在业务层返回封装的数据给前端时拦截afterCompletion方法：在视图渲染前进行拦截