import lombok.extern.slf4j.Slf4j;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * 登錄攔截器
 */
@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
    /**
     * 目標方法執(zhí)行之前執(zhí)行
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        // 獲取請求路徑
        String requestUrl = request.getRequestURI();
        log.info("請求的路徑是: {}", requestUrl);

        String username = request.getParameter("username");
        if (username != null) {
            // 放行
            return true;
        }

        request.setAttribute("msg", "請先登錄");
        // 攜帶msg跳轉到登錄頁
        request.getRequestDispatcher("/").forward(request, response);
        return false;
    }

    /**
     * 目標方法完成以后執(zhí)行
     * @param request
     * @param response
     * @param handler
     * @param modelAndView
     * @throws Exception
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("postHandle執(zhí)行");
    }

    /**
     * 頁面渲染以后執(zhí)行
     * @param request
     * @param response
     * @param handler
     * @param ex
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("afterCompletion執(zhí)行");
    }
}

import com.codeliu.interceptor.LoginInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

// 表示這是一個配置類
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor())
                .addPathPatterns("/**")  // 攔截所有路徑
                .excludePathPatterns("/","/login","/css/**","/fonts/**","/images/**","/js/**");  // 不攔截這些路徑
    }
}

// 執(zhí)行攔截器的preHandle方法，如果返回為fasle，則直接return，不執(zhí)行目標方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    return;
}

// 反射執(zhí)行目標方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

/**
 * Apply preHandle methods of registered interceptors.
 * @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.
 */
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
    // 遍歷攔截器
    for (int i = 0; i < this.interceptorList.size(); i++) {
        HandlerInterceptor interceptor = this.interceptorList.get(i);
        // 執(zhí)行當前攔截器的preHandle方法
        if (!interceptor.preHandle(request, response, this.handler)) {
            // 如果preHandle方法返回為false，則執(zhí)行當前攔截器的afterCompletion方法
            triggerAfterCompletion(request, response, null);
            return false;
        }
        // 記錄當前攔截器的下標
        this.interceptorIndex = i;
    }
    return true;
}

/**
 * Trigger afterCompletion callbacks on the mapped HandlerInterceptors.
 * Will just invoke afterCompletion for all interceptors whose preHandle invocation
 * has successfully completed and returned true.
 */
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) {
    // 反向遍歷攔截器
    for (int i = this.interceptorIndex; i >= 0; i--) {
        HandlerInterceptor interceptor = this.interceptorList.get(i);
        try {
            // 執(zhí)行當前攔截器的afterCompletion方法
            interceptor.afterCompletion(request, response, this.handler, ex);
        }
        catch (Throwable ex2) {
            logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
        }
    }
}

// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

mappedHandler.applyPostHandle(processedRequest, response, mv);

/**
 * Apply postHandle methods of registered interceptors.
 */
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
    throws Exception {
	// 反向遍歷
    for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
        HandlerInterceptor interceptor = this.interceptorList.get(i);
        // 執(zhí)行當前攔截器的postHandle方法
        interceptor.postHandle(request, response, this.handler, mv);
    }
}

processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);