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Spring-Filter-Interceptor-Exceptions

How to handle exceptions within Spring Filters and Interceptors

Filters and Interceptors have quite a different behaviour as they do not act at the same level. The project shows within the "config" package how to simply handle an exception and forward an according response.

• For an Interceptor, we only need an Exception Handler as we have access to the Spring MVC stack

• For a Filter, we need to catch the exception and handle it on the response (response.setStatus/response.getWriter().write(...))

Why

This example was initially made to answer the following use case : An existing filter/interceptor does some processing involving an external HTTP call with WebClient, and when the WebClient throws a WebClientResponseException indicating a specific issue & status code (400, 404, ...) it is not properly forwarded and always results in an Internal Error 500.

• Handling exceptions with interceptors may look more cumbersome in the code, but 2 of the classes are only involved in configuring the interceptor, the exception handler is easier to setup and it can be reused across the project.

• Filters can be more tricky (not forgetting to call the filterChain, not messing too much with the Servlets, serializing the JSON/.. to return, ..), they can't use a ControllerAdvice/ExceptionHandler as they happen before controllers are resolved, but they do not depend on the MVC stack