Spring MVC: how to to Handle Multipart File Upload with Custom Validation Logic
I'm a bit lost with I'm building a feature where I'm having trouble with file uploads in my Spring MVC application, particularly when I try to implement custom validation logic for the uploaded files..... I'm using Spring Boot 2.6.3 and I've set up my controller to handle multipart file uploads, but I keep running into issues with binding the file and validating it properly. Here’s a brief overview of what I’ve set up: In my `@Controller`, I have the following method: ```java @PostMapping("/upload") public String handleFileUpload(@RequestParam("file") MultipartFile file, BindingResult result) { if (result.hasErrors()) { return "uploadForm"; // Return to form if there are binding errors } // Custom validation logic if (file.isEmpty() || file.getSize() > 10485760) { // Limit to 10MB result.rejectValue("file", "behavior.file", "File must not be empty and should be less than 10MB"); return "uploadForm"; } // Process the file return "uploadSuccess"; } ``` In my form HTML, I have the following: ```html <form action="/upload" method="post" enctype="multipart/form-data"> <input type="file" name="file" /> <span th:if="${#fields.hasErrors('file')}" th:errors="*{file}"></span> <button type="submit">Upload</button> </form> ``` When I submit the form with a valid file, everything works perfectly. However, if I upload a file that exceeds the size limit, the form doesn't show the behavior message, and it simply redirects to the success page, which is not the desired behavior. I expect the form to return with the validation errors shown. I'm also not seeing any behavior messages in the logs that could give me a hint as to what's going wrong. Additionally, I've tried enabling multipart support in my application properties: ``` spring.servlet.multipart.enabled=true spring.servlet.multipart.max-file-size=10MB spring.servlet.multipart.max-request-size=10MB ``` I suspect the scenario might be related to how the `BindingResult` is handled, but I’m not sure how to fix it. Any insights or suggestions on how to properly implement this validation logic would be greatly appreciated! I'm working on a application that needs to handle this. I'd love to hear your thoughts on this. Any pointers in the right direction?