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Today, the editor will share with you the relevant knowledge about how to achieve SpringBoot interceptor and file upload in Java. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article. Let's take a look at it.

The concept of interceptor

Dynamically intercepting objects called by Actioon enables developers to execute a piece of code before and after the execution of an Actioon, or to prevent the execution of the Action before it is executed. it also provides a way to extract the reusable part of the code in the Action.

Function:

Dynamically intercept objects called by Action (that is, the interface of the controller layer in the actual project)

General interceptors are used to restrict user access. If you visit the main page when the user is not logged in, you can use the interceptor to intercept and redirect to the login page.

Configuration of interceptor

Create the interceptor folder and create the LoginInterceptor Java file and implement the interface HandlerInterceptor.

/ / you must implement the HandlerInterceptor interface public class LoginInterceptor implements HandlerInterceptor {/ * * before the target method executes * * / @ 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", "Please login!") ; / / response.sendRedirect ("/"); request.getRequestDispatcher ("/") .forward (request,response); return false } / / after the target method is executed, @ Override public void postHandle (HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {} / * the page is rendered after * @ 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) }} configure interceptor

Create the config folder and create the AdminWebConfig file and implement the addInterceptors of WebMvcConfigurer.

@ Configurationpublic class AdminWebConfig implements WebMvcConfigurer {@ Override public void addInterceptors (InterceptorRegistry registry) {registry.addInterceptor (new LoginInterceptor ()) .add PathPatterns ("/ * *") / / static paths will also be intercepted. IntercepdePathPatterns ("/", "/ login", "/ css/**", "/ fonts/**", "/ images/**", "/ js/**");} the principle of interceptor

1. According to the current request, find * * HandlerExecutionChain [* * handler that can handle the request and all interceptors of handler]

2. First-come and sequentially execute the preHandle method of all interceptors

1. If the current interceptor prehandler returns true. Then execute the preHandle of the next interceptor

2. If the current interceptor returns false. Directly reverse the afterCompletion of all interceptors that have been executed

3. If any interceptor returns false. Directly jump out of the non-execution target method

4. All interceptors return True. Execute the target method

5. Execute the postHandle method of all interceptors in reverse order.

6. Any exception in the previous step will directly trigger afterCompletion in reverse order.

7. After the successful rendering of the page, afterCompletion will also be triggered in reverse order.

File upload

We knew about the function of file upload when we studied SSM before, so we don't talk too much about it in SpringBoot, but the principle is pretty much the same.

Front-end files:

Configuration of the Controller layer:

@ Controllerpublic 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";}} change the file upload size

Configure the file size in application.properties:

Spring.servlet.multipart.max-file-size=10MB / / single file size

Spring.servlet.multipart.max-request-size=100MB / / multiple files

These are all the contents of the article "how to achieve SpringBoot interceptor and file upload in Java". Thank you for reading! I believe you will gain a lot after reading this article. The editor will update different knowledge for you every day. If you want to learn more knowledge, please pay attention to the industry information channel.

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