Provide a way to intercept requests and (optionally) prevent further handler(s) from being executed

The problem I’m experiencing is pretty simple: I need to intercept/filter a request and check a global variable that tells me whether the request can be processed or if, in turn, an error should be returned straight away, by-passing any handler configured for the path in question.

Just a little bit a code to illustrate:

            path("/v1", () -> {
                // global "failer", toggled by end-users
                before(ctx -> {
                    if (alwaysReturnError) {
                        ctx.response().sendError(INTERNAL_SERVER_ERROR_500);
                    }
                });
                path("/run", () -> {
                    post(ctx -> {
                        recordCall(RUN, ctx);
                        ctx.status(ACCEPTED_202).json(EMPTY_JSON_OBJECT);
                    });
                });

The before approach shown above does not work as expected, since the handler for /run is executed even after ctx.response().sendError(INTERNAL_SERVER_ERROR_500); was executed.

Is there any way to prevent (i.e. cut) the further processing of the request from within a before method? I strongly need this feature, so either recommending how to do it or adding it to the framework would be really helpful.

Kind Regards.

[tipsy]

Thanks, I’ve added

• You might know before-handlers as filters, interceptors, or middleware from other libraries.
• You might know endpoint-handlers as routes or middleware from other libraries.
• You might know after-handlers as filters, interceptors, or middleware from other libraries.

and

Javalin has a HaltException which is handled before other exceptions. It can be used to short-circuit the request lifecycle. If you throw a HaltException in a before-handler, no endpoint-handler will fire.

[ClintEsteMadera]

Silly me. You’re right. Perhaps mentioning the word “filter” and/or “interceptor” might help people find before and after easier.

Regarding HaltException it only states “which is handled before other exceptions”. Perhaps adding something more like “it can be used to prevent any other handler from processing the request” might help.

Actually, the combination of before and HaltException seems to be Javalin’s way to implement something close to a web filter, perhaps it makes sense to add a section for that?