WebFlux returning http.okay vice http.notFound - functional-programming

Question

New to WebFlux, reactive, and handlers. I've got things "working", but am not understanding why following code is returning "okay" with empty body, vice "not found".
Clarification: The issue-of-concern is in the final return statement of DemoPOJOHandler.getById(). The "short-circuit" code works as expected (i.e., returns "Bad Request" status), but the "switchIfEmpty" path of the final return statement does not appear to get exercised if a DemoPOJORepo.getById(int) returns Mono.empty().
(Note: I've hacked up a list-based "repo" to avoid dealing with database while figuring out handlers and http return types.)
Router implementation ("/v1" is a set of annotation based RESTful endpoints)...
#Configuration
public class DemoPOJORouter {
#Bean
public RouterFunction<ServerResponse> route(DemoPOJOHandler requestHandler) {
return nest(path("/v2"),
nest(accept(APPLICATION_JSON),
RouterFunctions.route(RequestPredicates.GET("/DemoPOJO"), requestHandler::getAll)
.andRoute(RequestPredicates.GET("/DemoPOJO/{id}"), requestHandler::getById)
.andRoute(RequestPredicates.POST("/DemoPOJO"), requestHandler::add)));
}
}
Handler implementation has been "stripped down" to only the code in question. I have a feeling that much of the style is "still imperative", but I've attempted to put the reactive stuff where it "makes the most sense".
If I supply a bad value on the URI (i.e., "foo"), then I get the http "bad request" returned. But, never seem to get the "not found" that should be generated by "switchIfEmpty" if a validly formatted int value is supplied, but it does not map to an entry in the repo.
#Component
public class DemoPOJOHandler {
public static final String PATH_VAR_ID = "id";
private DemoPOJORepo repo = null;
public Mono<ServerResponse> getById(ServerRequest request) {
Mono<DemoPOJO> monoDemoPOJO = null;
Map<String, String> pathVariables = request.pathVariables();
int id = -1;
checkRepoRef(); // part of the list hack
// short-circuit if request doesn't contain id (should never happen)
if ((pathVariables == null)
|| (!pathVariables.containsKey(PATH_VAR_ID))) {
return ServerResponse.badRequest().build();
}
// short-circuit if bad id value
try {
id = Integer.parseInt(pathVariables.get(PATH_VAR_ID));
} catch(NumberFormatException e) {
return ServerResponse.badRequest().build();
}
// get entity by keyValue
monoDemoPOJO = repo.getById(id);
return monoDemoPOJO
.flatMap(demoPOJO -> ServerResponse.ok()
.contentType(MediaType.APPLICATION_JSON)
.syncBody(demoPOJO)
.switchIfEmpty(ServerResponse.notFound().build()));
}
}
Hack of a list-based repo to avoid dealing with data/APIs while working on handlers and http return types.
// local hack to avoid a database for testing
public class DemoPOJORepo {
private static DemoPOJORepo fpRepo = null;
private static int NUM_ROWS = 100;
private Map<Integer, DemoPOJO> fooPOJOMap;
private DemoPOJORepo() {
initMap();
}
public static DemoPOJORepo getInstance() {
if (fpRepo == null) {
fpRepo = new DemoPOJORepo();
}
return fpRepo;
}
public Mono<DemoPOJO> getById(int id) {
Mono<DemoPOJO> monoDP;
if (fooPOJOMap.containsKey(id)) {
monoDP = Mono.just(fooPOJOMap.get(id));
} else {
monoDP = Mono.empty();
}
return monoDP;
}
private Mono<Void> initMap() {
fooPOJOMap = new TreeMap<Integer, DemoPOJO>();
int offset = -1;
for(int ndx=0; ndx<NUM_ROWS; ndx++) {
offset = ndx + 1;
fooPOJOMap.put(offset, new DemoPOJO(offset, "foo_" + offset, offset+100));
}
return Mono.empty();
}
}

Answer 1

Your brackets are in the wrong place causing the swithIfEmpy to apply to the ServerResponse.ok() publisher not the monoDemoPOJO, replace the return with this and it should work:
return monoDemoPOJO
.flatMap(demoPOJO -> ServerResponse.ok().contentType(MediaType.APPLICATION_JSON).syncBody(demoPOJO))
.switchIfEmpty(ServerResponse.notFound().build());

Answer 2

As I can see the code is right. The response code is Bad request because you are trying to convert "foo" to Integer, and when it throws an exception you are returning a Bad request response, so I think it works perfectly fine.
If you use an Integer id that is not present in your database then the answer must be a not found response