Send Restful API JSON response from Spring Boot Filter - spring

Question

I am using following filter for checking if a specific HTTP Header is present on api request.
#Component
#RequiredArgsConstructor
public class HeaderValidationFilter extends OncePerRequestFilter {
private final ObjectMapper objectMapper;
#Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
String headerValue = request.getHeader("RANDOM_HEADER");
if(Objects.isNull(headerValue)) {
ResponseEntity<Object> responseToSend = ResponseGen.create("FAILED", "Missing Authentication Header", new Object())));
response.setHeader("Content-Type", "application/json");
response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
response.getOutputStream().write(responseToSend);
return;
}
filterChain.doFilter(request, response);
}
It returns response as JSON but with added object keys like headers,statusCodeetc and the payload I provided is placed inside body. As I have a standard error response defined on the Project, I cannot return the response at it is. (See the following response)
{
"headers": {},
"body": {
"status": "FAILURE",
"message": "Missing Authentication Header",
"data": {}
},
"statusCode": "UNAUTHORIZED",
"statusCodeValue": 401
}
I want the response to be only in this format:
{
"status": "FAILED",
"message": "Missing Authentication Header",
"data": {}
}
I have tried returning using generic exception handler with #ControllerAdvice but it doesn't capture exception from Filters as it is executed before DispatcherServlet
Can someone help me out?

Answer 1

The JSON you see
{
"headers": {...},
"body": {...},
"statusCode": ...,
"statusCodeValue": ...
}
is the serialized ResponseEntity that you write as a response in your filter:
ResponseEntity<Object> responseToSend = ResponseGen.create("FAILED", "Missing Authentication Header", new Object())));
Obviously, if you need a response in another format you'll have to use an object that is serialized to the desired format as a response. E.g.
#Data
#AllArgsConstructor
class StandardError {
private String status;
private String message;
private Object data;
}
....
#Override
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response,
FilterChain filterChain) throws ServletException, IOException {
...
if (Objects.isNull(headerValue)) {
StandardError responseToSend = new StandardError("FAILED", "Missing Authentication Header", new Object());
response.setHeader("Content-Type", "application/json");
response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
response.getOutputStream().write(responseToSend);
return;
}
...