How to Validate a Specific Value in the Request Body of a POST Request in Spring Cloud Gateway MVC?

[marinusgeuze]

Hi,

In our Spring Cloud Gateway MVC project, we need to validate a specific value in the request body of a POST request before routing it to a downstream microservice.

The only solution we've found that works is the code snippet below. However, it feels somewhat cumbersome, and we're wondering if there's a cleaner, more idiomatic way to achieve this. We couldn't find a better approach in the Spring Cloud Gateway MVC documentation.

Could anyone suggest a more elegant solution?

Thanks in advance for your help!

Router configuration

    return route()
        .POST(
            “path”
            https())
        .before(validate())
        .build();
  }

Before filter

public static Function<ServerRequest, ServerRequest> validate() {

    return request -> {

      try {
        var clonedInputStream = cloneInputStream(request);
        var clonedRequest = adaptCachedBody().apply(request);
      
        Map<String, String> jsonRequest = new ObjectMapper().readValue(clonedInputStream, Map.class);
      
        // Reset stream so that it can be read again when request is routed to downstream MicroService
        clonedInputStream.reset();
      
        var field = jsonRequest.get("field");
      
        //Validate logic
      
        return clonedRequest;
      
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    };
  }

private static InputStream cloneInputStream(ServerRequest request) throws IOException {

  var inputStream = request.servletRequest().getInputStream();
  var byteArray = StreamUtils.copyToByteArray(inputStream);
  var clonedInputStream = new ByteArrayInputStream(byteArray);

  // This attribute is read by the adaptCachedBody function
  request.attributes().put(MvcUtils.CACHED_REQUEST_BODY_ATTR, clonedInputStream);

  return clonedInputStream;
}