Content Negotiation with Servlet Filter in Spring (Boot)
Update 2022-01-29: You may be interested in using spring-content-negotiator to make this simpler!
As noted in Content Negotiation with ControllerAdvice and ExceptionHandlers in Spring (Boot), content negotiation is useful for providing different representations of formats for clients.
(I'd recommend a read of that article before this one to understand a bit more of the context for what is recommended below.)
However, you may also want to be doing this when handling errors in Filters, which doesn't work as nicely.
Note that this will only work with Spring, as this depends on Spring classes.
Let's assume that we have the following filter that performs error handling:
@Component
public class CorrelationIdFilter extends OncePerRequestFilter {
private final ObjectMapper objectMapper;
public CorrelationIdFilter(ObjectMapper objectMapper) {
this.objectMapper = objectMapper;
}
@Override
protected void doFilterInternal(
HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
String uuid = request.getHeader("correlation-id");
if (uuid == null) {
uuid = UUID.randomUUID().toString();
}
if (!uuid.matches(Patterns.UUID_STRING)) {
handleInvalidCorrelationId(response);
return; // make sure you have this set!
}
try {
filterChain.doFilter(request, response);
} finally {
response.addHeader("correlation-id", uuid);
}
}
private void handleInvalidCorrelationId(HttpServletResponse response) throws IOException {
ErrorResponse errorResponse = new ErrorResponse();
errorResponse.setError(ErrorResponse.Error.INVALID_REQUEST);
errorResponse.setErrorDescription("The correlation-id is not a valid UUID.");
response.setContentType("application/json");
response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
response.getWriter().write(objectMapper.writeValueAsString(errorResponse));
}
}
But we know that we may receive two types of API call, one that requests application/json, and one that requires text/plain, and we need to return the appropriate error response.
We can instead rewrite the Filter to perform content-negotiation and return the right representation:
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.UUID;
import java.util.stream.Collectors;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import me.jvt.contentnegotiation.ContentTypeNegotiator;
import me.jvt.contentnegotiation.NotAcceptableException;
import me.jvt.uuid.Patterns;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.accept.ContentNegotiationManager;
import org.springframework.web.filter.OncePerRequestFilter;
import org.springframework.web.servlet.handler.DispatcherServletWebRequest;
import uk.gov.api.models.metadata.ErrorResponse;
@Component
public class CorrelationIdFilter extends OncePerRequestFilter {
private final ObjectMapper objectMapper;
private final ContentNegotiationManager contentNegotiationManager;
public CorrelationIdFilter(
ObjectMapper objectMapper, ContentNegotiationManager contentNegotiationManager) {
this.objectMapper = objectMapper;
this.contentNegotiationManager = contentNegotiationManager;
}
@Override
protected void doFilterInternal(
HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
String uuid = request.getHeader("correlation-id");
if (uuid == null) {
uuid = UUID.randomUUID().toString();
}
if (!uuid.matches(Patterns.UUID_STRING)) {
handleInvalidCorrelationId(request, response);
return; // make sure you have this set!
}
try {
filterChain.doFilter(request, response);
} finally {
response.addHeader("correlation-id", uuid);
}
}
private void handleInvalidCorrelationId(HttpServletRequest request, HttpServletResponse response)
throws IOException {
ContentTypeNegotiator negotiator = negotiator("application/json", "text/plain");
MediaType resolved;
try {
resolved = resolve(request, negotiator);
} catch (HttpMediaTypeNotAcceptableException ex) {
response.setStatus(HttpServletResponse.SC_NOT_ACCEPTABLE);
return;
}
if (MediaType.valueOf("application/json").isCompatibleWith(resolved)) {
ErrorResponse errorResponse = new ErrorResponse();
errorResponse.setError(ErrorResponse.Error.INVALID_REQUEST);
errorResponse.setErrorDescription("The correlation-id is not a valid UUID.");
response.setContentType(resolved.toString());
response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
response.getWriter().write(objectMapper.writeValueAsString(errorResponse));
} else if (MediaType.valueOf("text/plain").isCompatibleWith(resolved)) {
response.setContentType(resolved.toString());
response.setStatus(HttpServletResponse.SC_BAD_REQUEST);
response.getWriter().write("The correlation-id is not a valid UUID.");
} else {
throw new IllegalStateException("MediaType " + resolved + " not handled");
}
}
private MediaType resolve(HttpServletRequest request, ContentTypeNegotiator negotiator)
throws HttpMediaTypeNotAcceptableException {
List<MediaType> mediaTypes =
contentNegotiationManager.resolveMediaTypes(new DispatcherServletWebRequest(request));
List<me.jvt.http.mediatype.MediaType> converted =
mediaTypes.stream().map(me.jvt.http.mediatype.MediaType::from).collect(Collectors.toList());
try {
me.jvt.http.mediatype.MediaType negotiated = negotiator.negotiate(converted);
return MediaType.valueOf(negotiated.toString());
} catch (NotAcceptableException e) {
throw new HttpMediaTypeNotAcceptableException(e.getMessage());
}
}
private static List<me.jvt.http.mediatype.MediaType> supported(String... mediaTypes) {
return Arrays.stream(mediaTypes)
.map(me.jvt.http.mediatype.MediaType::valueOf)
.collect(Collectors.toList());
}
private static ContentTypeNegotiator negotiator(String... mediaTypes) {
return new ContentTypeNegotiator(supported(mediaTypes));
}
}
Which we can see working below:
% curl localhost:8080/apis -i -H 'Correlation-ID: 12' -H "accept: text/p
lain"
HTTP/1.1 400
Content-Type: text/plain;charset=ISO-8859-1
Content-Length: 39
Date: Tue, 18 Jan 2022 11:58:34 GMT
Connection: close
The correlation-id is not a valid UUID
% curl localhost:8080/apis -i -H 'Correlation-ID: 12' -H "accept: application/json"
HTTP/1.1 400
Content-Type: application/json;charset=ISO-8859-1
Content-Length: 89
Date: Tue, 18 Jan 2022 11:59:00 GMT
Connection: close
{"error":"invalid_request","error-description":"The correlation-id is not a valid UUID."}
