攔截器可以攔截請求也可以攔截響應。使用攔截器的步驟如下： <br/> **1. 實現接口HandlerInterceptor** ```java import org.springframework.web.servlet.HandlerInterceptor; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class LoginHandlerInterceptor implements HandlerInterceptor { /** * 在執行目標方法之前先執行該方法 * 當return false時將其攔截 * 當return true時將其放行 */ public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { // session.setAttribute("user", user) Object user = request.getSession().getAttribute("user"); if (user == null) { request.setAttribute("msg", "請先登錄！"); request.getRequestDispatcher("/login").forward(request, response); return false; } else { return true; } } /** * 在后端響應數據到前端之前該方法被調用 * * @param request * @param response * @param handler * @param modelAndView * @throws Exception */ @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { System.out.println("postHandle"); } /** * 響應完成之后該方法被調用，可以在這個方法中做一些釋放資源的工作 * * @param request * @param response * @param handler * @param ex * @throws Exception */ @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { System.out.println("afterCompletion"); } } ``` **2. 注冊攔截器到IoC容器中** ```java import com.example.webresult.component.LoginHandlerInterceptor; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.web.servlet.config.annotation.InterceptorRegistry; import org.springframework.web.servlet.config.annotation.ViewControllerRegistry; import org.springframework.web.servlet.config.annotation.WebMvcConfigurer; @Configuration public class CustomMvcConfig implements WebMvcConfigurer { @Bean public WebMvcConfigurer webMvcConfigurer() { WebMvcConfigurer webMvcConfigurer = new WebMvcConfigurer() { @Override public void addInterceptors(InterceptorRegistry registry) { //addPathPatterns 要攔截的請求，/*表示攔截所有請求 //excludePathPatterns 不攔截的請求 registry.addInterceptor(new LoginHandlerInterceptor()).addPathPatterns("/*") .excludePathPatterns("/login", "/", "/doLogin"); } }; return webMvcConfigurer; } } ```