How to retry RestAPI connection if it fails for first time in restTemplate? - spring-boot

Question

I am calling a third party rest API, some times it sends response with status code 500, 504.
I want to make a another hit to the API if it gives above status code.
My current logic of retry is:
public <T> ResponseEntity<T> sendGetRequest(String url,
Class<T> responseClazz,
HttpHeaders headers) {
ResponseEntity<T> response = null;
int count = 0;
int maxTries = 2;
while(true) {
try {
HttpEntity request = new HttpEntity(headers);
response = restTemplate.exchange(url, HttpMethod.GET, request, responseClazz);
if(response.getStatusCode() != HttpStatus.OK) {
log.error("null or Error response from server for ", url);
}
log.info("Response received {}", response.toString());
return response;
}catch (ResourceAccessException rae){
log.warn("retry count {} {}", count, rae);
if (++count == maxTries) throw new ServerErrorException("API timeout");
}
}
}
I have also used apache http where I use CloseableHttpClient to retry for status code 500 and 504.
I have also looks to the solution of spring-retry. Is there any other method to do this?

Answer 1

When calling HTTP request with RestTemplate, there are 2 main cases to retry:
Specific response HTTP statuses. For example:
503 Service Unavailable status can be retried.
404 Not Found can be proceeded without a retry attempt.
ResourceAccessException which can represent some IO exception received without getting the HTTP server response, like SocketException: Broken pipe.
For solution based on RestTemplate/HttpClient, while it exposes options to retry based on the HTTP response, combining it with IOException handling can be tricky.
Solution based on Spring RetryTemplate
#Bean(name = "restTemplateRetryTemplate")
public RetryTemplate restTemplateRetryTemplate() {
return createRestTemplateRetryTemplate();
}
private RetryTemplate createRestTemplateRetryTemplate(boolean retryOnServerErrors) {
Map<Class<? extends Throwable>, Boolean> retryableExceptions = new HashMap<>();
retryableExceptions.put(ResourceAccessException.class, true);
retryableExceptions.put(HttpServerErrorException.ServiceUnavailable.class, true);
retryableExceptions.put(HttpServerErrorException.BadGateway.class, true);
retryableExceptions.put(HttpServerErrorException.GatewayTimeout.class, true);
retryableExceptions.put(HttpClientErrorException.TooManyRequests.class, true);
return createRetryTemplate(retryableExceptions);
}
private RetryTemplate createRetryTemplate(Map<Class<? extends Throwable>, Boolean> retryableExceptions) {
RetryTemplate retryTemplate = new RetryTemplate();
ExponentialRandomBackOffPolicy exponentialRandomBackOffPolicy = new ExponentialRandomBackOffPolicy();
exponentialRandomBackOffPolicy.setInitialInterval(INITIAL_INTERVAL);
exponentialRandomBackOffPolicy.setMaxInterval(MAX_INTERVAL);
exponentialRandomBackOffPolicy.setMultiplier(MULTIPLIER);
retryTemplate.setBackOffPolicy(exponentialRandomBackOffPolicy);
retryTemplate.setRetryPolicy(new SimpleRetryPolicy(MAX_ATTEMPTS, retryableExceptions));
// Optional, for additional logging on failures.
retryTemplate.registerListener(retryTemplateLogListener);
return retryTemplate;
}
Usage example
#Autowired
#Qualifier("restTemplateRetryTemplate")
private RetryTemplate retryTemplate;
...
String result = retryTemplate.execute(arg -> {
return longRestTemplate.getForObject(url, String.class);
});