java - How to manage exceptions thrown in filters in Spring?

Question

I want to use generic way to manage 5xx error codes, let's say specifically the case when the db is down across my whole spring application. I want a pretty error json instead of a stack trace.

For the controllers I have a @ControllerAdvice class for the different exceptions and this is also catching the case that the db is stopping in the middle of the request. But this is not all. I also happen to have a custom CorsFilter extending OncePerRequestFilter and there when i call doFilter i get the CannotGetJdbcConnectionException and it will not be managed by the @ControllerAdvice. I read several things online that only made me more confused.

So I have a lot of questions:

• Do i need to implement a custom filter? I found the ExceptionTranslationFilter but this only handles AuthenticationException or AccessDeniedException.
• I thought of implementing my own HandlerExceptionResolver, but this made me doubt, I don't have any custom exception to manage, there must be a more obvious way than this. I also tried to add a try/catch and call an implementation of the HandlerExceptionResolver (should be good enough, my exception is nothing special) but this is not returning anything in the response, i get a status 200 and an empty body.

Is there any good way to deal with this? Thanks

Answer 1

So this is what I did:

I read the basics about filters here and I figured out that I need to create a custom filter that will be first in the filter chain and will have a try catch to catch all runtime exceptions that might occur there. Then i need to create the json manually and put it in the response.

So here is my custom filter:

public class ExceptionHandlerFilter extends OncePerRequestFilter {

    @Override
    public void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        try {
            filterChain.doFilter(request, response);
        } catch (RuntimeException e) {

            // custom error response class used across my project
            ErrorResponse errorResponse = new ErrorResponse(e);

            response.setStatus(HttpStatus.INTERNAL_SERVER_ERROR.value());
            response.getWriter().write(convertObjectToJson(errorResponse));
    }
}

    public String convertObjectToJson(Object object) throws JsonProcessingException {
        if (object == null) {
            return null;
        }
        ObjectMapper mapper = new ObjectMapper();
        return mapper.writeValueAsString(object);
    }
}

And then i added it in the web.xml before the CorsFilter. And it works!

<filter> 
    <filter-name>exceptionHandlerFilter</filter-name> 
    <filter-class>xx.xxxxxx.xxxxx.api.controllers.filters.ExceptionHandlerFilter</filter-class> 
</filter> 


<filter-mapping> 
    <filter-name>exceptionHandlerFilter</filter-name> 
    <url-pattern>/*</url-pattern> 
</filter-mapping> 

<filter> 
    <filter-name>CorsFilter</filter-name> 
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class> 
</filter> 

<filter-mapping>
    <filter-name>CorsFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>