Vertx - using the Router failureHandler for the errors in async calls - vert.x

Question

We have recently discovered the failureHandler in the Vertx router
We thought it could help us get rid of all the repetitive try-catch blocks we have. But alas, it seems that the exceptions that are thrown inside the callbacks are not caught by the failureHandler.
Example: below, the failureHandler is called only for the 3rd case:
// Get the user details
router.get("/user").handler(ctx -> {
ctx.response().headers().add("content-type", "application/json");
// some async operation
userApiImpl.getUser(ctx, httpClient, asyncResult -> {
// ctx.response().setStatusCode(404).end(); //1
// throw new RuntimeException("sth happened"); //2
ctx.fail(404); //3
});
});
// ============================
// ERROR HANDLER
// ============================
router.get("/user").failureHandler(ctx -> {
LOG.info("Error handler is in the action.");
ctx.response().setStatusCode(ctx.statusCode()).end("Error occurred in method");
});
Is this as expected?
Can we somehow declare a global try-catch in a router for the exceptions occurring in the async context?

Answer 1

It is expected that sending a response manually with an error code does not trigger the failure handler.
It should be triggered if:
the route path matches
a handler throws an exception or ctx.fail() is invoked
Here's an example:
Route route1 = router.get("/somepath/path1/");
route1.handler(routingContext -> {
// Let's say this throws a RuntimeException
throw new RuntimeException("something happened!");
});
Route route2 = router.get("/somepath/path2");
route2.handler(routingContext -> {
// This one deliberately fails the request passing in the status code
// E.g. 403 - Forbidden
routingContext.fail(403);
});
// Define a failure handler
// This will get called for any failures in the above handlers
Route route3 = router.get("/somepath/*");
route3.failureHandler(failureRoutingContext -> {
int statusCode = failureRoutingContext.statusCode();
// Status code will be 500 for the RuntimeException or 403 for the other failure
HttpServerResponse response = failureRoutingContext.response();
response.setStatusCode(statusCode).end("Sorry! Not today");
});
See the error handling section of the Vert.x Web documentation