How to return response as Json from spring filter? - spring

Question

In spring rest I need to send authentication error from doFilter() of my filter class. In response i need to send json with fields like status, message and errorCode. Kindly suggest how to achieve. We are not using spring boot.Below is the sample response on Authentication error
{ "responseCode":" Error code",
"responseMessage": "Some Error message",
"responseStatus":"Fail"
}
Inside doFiler(), i am validating token, if its not valid I need to send above sample response.

Answer 1

Assuming you have Jackson's ObjectMapper exposed as a Spring bean, you could use the following for a OncePerRequestFilter:
#Component
#RequiredArgsConstructor
public class MyFilter extends OncePerRequestFilter {
private final ObjectMapper mapper;
#Override
protected void doFilterInternal(HttpServletRequest httpServletRequest,
HttpServletResponse httpServletResponse,
FilterChain filterChain) throws IOException {
Map<String, Object> errorDetails = new HashMap<>();
errorDetails.put("message", "Invalid token");
httpServletResponse.setStatus(HttpStatus.FORBIDDEN.value());
httpServletResponse.setContentType(MediaType.APPLICATION_JSON_VALUE);
mapper.writeValue(httpServletResponse.getWriter(), errorDetails);
}
}
For a plain servlet Filter, the solution would be much the same:
#Component
#RequiredArgsConstructor
public class MyFilter implements Filter {
private final ObjectMapper mapper;
#Override
public void init(FilterConfig filterConfig) {
}
#Override
public void doFilter(ServletRequest servletRequest,
ServletResponse servletResponse,
FilterChain filterChain) throws IOException {
HttpServletResponse httpServletResponse = (HttpServletResponse) servletResponse;
Map<String, Object> errorDetails = new HashMap<>();
errorDetails.put("message", "Invalid token");
httpServletResponse.setStatus(HttpStatus.FORBIDDEN.value());
httpServletResponse.setContentType(MediaType.APPLICATION_JSON_VALUE);
mapper.writeValue(httpServletResponse.getWriter(), errorDetails);
}
#Override
public void destroy() {
}
}
The above examples rely on constructor injection and use Lombok's #RequiredArgsConstructor to generate a constructor that receives values for the fields marked with final.
You also could replace the Map<String, Object> for any arbitrary POJO, according to your needs.