//必須實現(xiàn)HandlerInterceptor這個接口
public class LoginInterceptor implements HandlerInterceptor {
    /*
    * 目標方法執(zhí)行以前
    * */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        HttpSession session = request.getSession();
        Object loginUser = session.getAttribute("loginUser");
        if(loginUser != null) {
            return true;
        }
        request.setAttribute("msg" ,"請登錄！");
//        response.sendRedirect("/");
        request.getRequestDispatcher("/").forward(request,response);
        return  false;
    }
    //目標方法執(zhí)行以后
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    }
    /**
     * 頁面渲染以后
     * @param request
     * @param response
     * @param handler
     * @param ex
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
    }
}

配置攔截器

創(chuàng)建 config 文件夾并創(chuàng)建 AdminWebConfig 文件并實現(xiàn)WebMvcConfigurer的addInterceptors。

@Configuration
public class AdminWebConfig implements WebMvcConfigurer {
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LoginInterceptor())
                .addPathPatterns("/**") //靜態(tài)路徑也會被攔截
                .excludePathPatterns("/","/login","/css/**","/fonts/**" ,"/images/**","/js/**");
    }
}

攔截器的原理

1、根據(jù)當前請求，找到**HandlerExecutionChain【**可以處理請求的handler以及handler的所有攔截器】

2、先來順序執(zhí)行所有攔截器的 preHandle方法

1、如果當前攔截器prehandler返回為true。則執(zhí)行下一個攔截器的preHandle
2、如果當前攔截器返回為false。直接倒序執(zhí)行所有已經(jīng)執(zhí)行了的攔截器的 afterCompletion；

3、如果任何一個攔截器返回false。直接跳出不執(zhí)行目標方法

4、所有攔截器都返回True。執(zhí)行目標方法

5、倒序執(zhí)行所有攔截器的postHandle方法。

6、前面的步驟有任何異常都會直接倒序觸發(fā) afterCompletion

7、頁面成功渲染完成以后，也會倒序觸發(fā) afterCompletion

文件上傳

在之前我們學習SSM的時候就知道了文件上傳這個功能，所以在 SpringBoot中我們就不在過多介紹，原理其實都差不多。

前端文件：

<form method="post" action="/upload" enctype="multipart/form-data">
    <input type="file" name="file"><br>
    <input type="submit" value="提交">
</form>

Controller層的配置：

@Controller
public class FileController {
    @GetMapping("/updateFile")
    public String FileUp(){
        return "FileUp";
    }  
@PostMapping("/upload") // //new annotation since 4.3
    public String singleFileUpload(@RequestParam("file") MultipartFile file,
                                   RedirectAttributes redirectAttributes) {
        if (file.isEmpty()) {
            redirectAttributes.addFlashAttribute("message", "Please select a file to upload");
            return "redirect:uploadStatus";
        }
        try {
            // Get the file and save it somewhere
            byte[] bytes = file.getBytes();
            Path path = Paths.get( file.getOriginalFilename());
            Files.write(path, bytes);
            redirectAttributes.addFlashAttribute("message",
                    "You successfully uploaded '" + file.getOriginalFilename() + "'");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return "redirect:/main.html";
    }
}