Spring WebClient Retry Logic with new Headers

I am trying to build a retry logic using Spring WebClient. The problem that I am trying to solve is very simple. I am calling an API endpoint to get some values. If the API returns an error with say 401 response, then I will have to make call to Token service and renew my token and use the new token and make the same API call.

The general psudo is

try {
    GET /locations data
} catch(401 Unauthorized) {
    POST /token and get renew Token --> This is another WebClient API call With New Token
    call again GET /locations and return value
} catch (Another Exception) {
    throw Application Error
}

Here is the Spring code that I am trying to do and it does not look like it is working. Any suggestion on how to do it.

public List<Location> getLocations(final User user) {
    if (null == user) {
        throw new ApplicationException("User cannot be null");
    }

    if (null == user.getHoneyWellLinkToken()) {
        throw new ApplicationException(String.format("%s has not linked the account with Honeywell", user.getUsername()));
    }


    List<Location> locations = getLocationsAPI(user).block();

    return locations;

}

private Mono<List<Location>> getLocationsAPI(final User user) {
    String endpoint = config.getApi().getLocationsEndpoint()
                .concat("?apikey=")
                .concat(config.getCredentials().getClientId());

    return WebClient.builder().baseUrl(endpoint)
                .build()
                .get()
                .headers(httpHeaders -> httpHeaders.setBearerAuth(user.getHoneyWellLinkToken().getAccessToken()))
                .retrieve()
                .bodyToFlux(Location.class)
                .collectList()
                .doOnError(err -> {
                    WebClient.builder().baseUrl(endpoint)
                            .build()
                            .get()
                            .headers(httpHeaders -> httpHeaders.setBearerAuth(honeywellService.renewToken(user).block().getHoneyWellLinkToken().getAccessToken()))
                            .retrieve().bodyToFlux(Location.class);

                });

}

This code is hosted on GitHub https://github.com/reflexdemon/home-use/blob/main/src/main/java/io/vpv/homeuse/service/HoneywellThermostatService.java

Answer

• Use onErrorResume instead of doOnError
• Do not block when renewing token

    private Mono<List<Location>> getLocationsAPI(final User user) {
        String endpoint = config.getApi().getLocationsEndpoint()
                                .concat("?apikey=")
                                .concat(config.getCredentials().getClientId());

        return getLocations(endpoint, user)
            .onErrorResume(err -> honeywellService.renewToken(user)
                                                  .flatMap(newUser -> getLocations(endpoint, newUser)));

    }

    private Mono<List<Location>> getLocations(String endpoint, User user) {
        return WebClient.builder()
                        .baseUrl(endpoint)
                        .build()
                        .get()
                        .headers(httpHeaders -> httpHeaders.setBearerAuth(user
                            .getHoneyWellLinkToken()
                            .getAccessToken()))
                        .retrieve()
                        .bodyToFlux(Location.class)
                        .collectList();
    }

Also, it’s a good idea to use a single WebClient instance instead of building a new one for each request.