I am currently developing an API using Spring Boot 3 with a POST endpoint that utilizes @RequestBody to receive requests. However, I’ve encountered an issue: @RequestBody only processes requests with the Content-Type set to application/json.

I would like to configure my API to accept and process JSON data regardless of the Content-Type header. This means that even if the Content-Type is missing or set to something else (e.g., text/plain or application/x-www-form-urlencoded), I want to parse the request body as JSON into my RequestDto.

What would be the best approach to achieve this functionality in Spring Boot?

To achieve this, I attempted to replace @RequestBody with HttpServletRequest in my controller and manually convert the request body using ObjectMapper:

@PostMapping("/api")
public ResponseEntity<?> handleRequest(HttpServletRequest request) throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();
    RequestDto dto = objectMapper.readValue(request.getInputStream(), RequestDto.class);
    // Proceed with processing
}

However, this approach has some drawbacks:

Validation Issues: I lose the ability to use the validation annotations (@Valid, @NotNull, etc.) that I have defined in my RequestDto. Implementing validation manually in the controller would complicate the code.

Code Maintainability: Writing custom parsing and validation logic in every controller method is not ideal.

Next, I tried using a filter to override the Content-Type header in incoming requests, hoping that Spring would process the request body as JSON regardless of the original Content-Type. Here’s the code I used in my filter:

public class ContentTypeOverrideFilter implements Filter {

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain)
            throws IOException, ServletException {

        HttpServletRequestWrapper servletRequestWrapper = new HttpServletRequestWrapper(
                (HttpServletRequest) servletRequest) {
            @Override
            public String getContentType() {
                return MediaType.APPLICATION_JSON_VALUE;
            }
        };

        chain.doFilter(servletRequestWrapper, servletResponse);
    }
}

This solution works when the Content-Type header is absent in the request. However, when the request has a Content-Type specified, the override does not take effect, and the request is not processed as JSON.

Question:

• How can I configure my Spring Boot application to process JSON data in POST requests regardless of the Content-Type header, while still utilizing the validation annotations in my RequestDto?
• Is there a way to globally override or ignore the Content-Type header for specific endpoints or for the entire application, so that all request bodies are treated as JSON?
• Alternatively, is there a better approach to achieve this functionality without losing the benefits of @RequestBody and validation annotations?