Make simple servlet filter work with #ControllerAdvice - spring

Question

I've a simple filter just to check if a request contains a special header with static key - no user auth - just to protect endpoints. The idea is to throw an AccessForbiddenException if the key does not match which then will be mapped to response with a class annotated with #ControllerAdvice. However I can't make it work. My #ExceptionHandler isn't called.
ClientKeyFilter
import org.springframework.beans.factory.annotation.Value
import org.springframework.stereotype.Controller
import javax.servlet.*
import javax.servlet.http.HttpServletRequest
#Controller //I know that #Component might be here
public class ClientKeyFilter implements Filter {
#Value('${CLIENT_KEY}')
String clientKey
public void init(FilterConfig filterConfig) {}
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) {
req = (HttpServletRequest) req
def reqClientKey = req.getHeader('Client-Key')
if (!clientKey.equals(reqClientKey)) {
throw new AccessForbiddenException('Invalid API key')
}
chain.doFilter(req, res)
}
public void destroy() {}
}
AccessForbiddenException
public class AccessForbiddenException extends RuntimeException {
AccessForbiddenException(String message) {
super(message)
}
}
ExceptionController
#ControllerAdvice
class ExceptionController {
static final Logger logger = LoggerFactory.getLogger(ExceptionController)
#ExceptionHandler(AccessForbiddenException)
public ResponseEntity handleException(HttpServletRequest request, AccessForbiddenException e) {
logger.error('Caught exception.', e)
return new ResponseEntity<>(e.getMessage(), I_AM_A_TEAPOT)
}
}
Where I'm wrong? Can simple servlet filter work with spring-boot's exception mapping?

Answer 1

As specified by the java servlet specification Filters execute always before a Servlet is invoked. Now a #ControllerAdvice is only useful for controller which are executed inside the DispatcherServlet. So using a Filter and expecting a #ControllerAdvice or in this case the #ExceptionHandler, to be invoked isn't going to happen.
You need to either put the same logic in the filter (for writing a JSON response) or instead of a filter use a HandlerInterceptor which does this check. The easiest way is to extend the HandlerInterceptorAdapter and just override and implement the preHandle method and put the logic from the filter into that method.
public class ClientKeyInterceptor extends HandlerInterceptorAdapter {
#Value('${CLIENT_KEY}')
String clientKey
#Override
public boolean preHandle(ServletRequest req, ServletResponse res, Object handler) {
String reqClientKey = req.getHeader('Client-Key')
if (!clientKey.equals(reqClientKey)) {
throw new AccessForbiddenException('Invalid API key')
}
return true;
}
}

Answer 2

You can't use #ControllerAdvice, because it gets called in case of an exception in some controller, but your ClientKeyFilter is not a #Controller.
You should replace the #Controller annotation with the #Component and just set response body and status like this:
#Component
public class ClientKeyFilter implements Filter {
#Value('${CLIENT_KEY}')
String clientKey
public void init(FilterConfig filterConfig) {
}
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
String reqClientKey = request.getHeader("Client-Key");
if (!clientKey.equals(reqClientKey)) {
response.sendError(HttpServletResponse.SC_FORBIDDEN, "Invalid API key");
return;
}
chain.doFilter(req, res);
}
public void destroy() {
}
}

Answer 3

Servlet Filters in Java classes are used for the following purposes:
To check requests from client before they access resources at backend.
To check responses from server before sent back to the client.
Exception throw from Filter may not be catch by #ControllerAdvice because in may not reach DispatcherServlet. I am handling in my project as below:
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws IOException, ServletException {
String token = null;
String bearerToken = request.getHeader("Authorization");
if (bearerToken != null && (bearerToken.contains("Bearer "))) {
if (bearerToken.startsWith("Bearer "))
token = bearerToken.substring(7, bearerToken.length());
try {
AuthenticationInfo authInfo = TokenHandler.validateToken(token);
logger.debug("Found id:{}", authInfo.getId());
authInfo.uri = request.getRequestURI();
AuthPersistenceBean persistentBean = new AuthPersistenceBean(authInfo);
SecurityContextHolder.getContext().setAuthentication(persistentBean);
logger.debug("Found id:'{}', added into SecurityContextHolder", authInfo.getId());
} catch (AuthenticationException authException) {
logger.error("User Unauthorized: Invalid token provided");
raiseException(request, response);
return;
} catch (Exception e) {
raiseException(request, response);
return;
}
// Wrapping the error response
private void raiseException(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException {
response.setContentType(MediaType.APPLICATION_JSON_VALUE);
response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
ApiError apiError = new ApiError(HttpStatus.UNAUTHORIZED);
apiError.setMessage("User Unauthorized: Invalid token provided");
apiError.setPath(request.getRequestURI());
byte[] body = new ObjectMapper().writeValueAsBytes(apiError);
response.getOutputStream().write(body);
}
// ApiError class
public class ApiError {
// 4xx and 5xx
private HttpStatus status;
// holds a user-friendly message about the error.
private String message;
// holds a system message describing the error in more detail.
private String debugMessage;
// returns the part of this request's URL
private String path;
public ApiError(HttpStatus status) {
this();
this.status = status;
}
//setter and getters