Retry java RestTemplate HTTP request if host offline

Question

Hi I\'m using the spring RestTemplate for calling a REST API. The API can be very slow or even offline. My application is building the cache by sending thousand

Answer 1

You can also tackle this annotation-driven using Spring Retry. This way you will avoid to implement the template.

Add it to your pom.xml

<dependency>
    <groupId>org.springframework.retry</groupId>
    <artifactId>spring-retry</artifactId>
    <version>1.1.2.RELEASE</version>
</dependency>

Enable it for your application/configuration

@SpringBootApplication
@EnableRetry
public class MyApplication {
  //...
}

Guard methods that are in danger of failure with @Retryable

@Service
public class MyService {

  @Retryable(maxAttempts=5, value = RuntimeException.class, 
             backoff = @Backoff(delay = 15000, multiplier = 2))
  public List<String> doDangerousOperationWithExternalResource() {
     // ...
  }

}

Answer 2

I had same situation and done some googling found the solution. Giving answer in hope it help someone else. You can set max try and time interval for each try.

@Bean
  public RetryTemplate retryTemplate() {

    int maxAttempt = Integer.parseInt(env.getProperty("maxAttempt"));
    int retryTimeInterval = Integer.parseInt(env.getProperty("retryTimeInterval"));

    SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();
    retryPolicy.setMaxAttempts(maxAttempt);

    FixedBackOffPolicy backOffPolicy = new FixedBackOffPolicy();
    backOffPolicy.setBackOffPeriod(retryTimeInterval); // 1.5 seconds

    RetryTemplate template = new RetryTemplate();
    template.setRetryPolicy(retryPolicy);
    template.setBackOffPolicy(backOffPolicy);

    return template;
  }

And my rest service that i want to execute is below.

retryTemplate.execute(context -> {
        System.out.println("inside retry method");
        ResponseEntity<?> requestData = RestTemplateProvider.getInstance().postAsNewRequest(bundle, ServiceResponse.class, serivceURL,
                CommonUtils.getHeader("APP_Name"));

        _LOGGER.info("Response ..."+ requestData);
            throw new IllegalStateException("Something went wrong");
        });

Answer 3

Use Spring Retry project (https://dzone.com/articles/spring-retry-ways-integrate, https://github.com/spring-projects/spring-retry).

It is designed to solve problems like yours.