RetryableStatusCodeException in Spring: Handling Retryable HTTP Errors

DigitalWeb Devs - June 2021

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Table of Contents

1. Introduction
2. Understanding RetryableStatusCodeException
3. Implementing RetryableStatusCodeException in Spring
4. Example Code
5. Conclusion
6. References

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1. Introduction

In any web application, dealing with various HTTP responses is inevitable. However, when we encounter temporary errors such as a failed connection or a server timeout, it is often desirable to provide a way for the application to automatically retry the operation. To aid in handling such situations, the Spring framework provides a convenient feature called RetryableStatusCodeException. In this article, we will explore how to utilize this exception in Spring applications to transparently retry HTTP requests without the need for manual intervention.

2. Understanding RetryableStatusCodeException

The RetryableStatusCodeException class is a part of the Spring web module and is specifically designed to handle retryable HTTP status codes. By default, the exception is configured to automatically retry requests for certain HTTP error codes that are deemed to be temporary, such as “503 Service Unavailable” or “504 Gateway Timeout”.

This exception extends the HttpClientErrorException class, which is thrown when an HTTP 4xx client error occurs. The primary difference is that the RetryableStatusCodeException signals that the request can be retried, while the HttpClientErrorException suggests some client-side issue. When a RetryableStatusCodeException is thrown, it serves as a signal to the RestTemplate (or any other component utilizing it) to retry the failed request automatically.

This retry mechanism is especially useful in situations where network instability might cause intermittent failures, and it helps to keep the application resilient by automatically retrying potentially transient issues.

3. Implementing RetryableStatusCodeException in Spring

To enable the automatic retry mechanism using RetryableStatusCodeException, we need to follow a few simple steps:

1. Configure the RestTemplate bean, which will handle HTTP requests in our Spring application.
2. Define a ResponseErrorHandler implementation to handle any HTTP errors and decide whether they should trigger an automatic retry or not.
3. Register the ResponseErrorHandler with the RestTemplate instance.

4. Example Code

Using the Spring framework, let’s dive into an example to demonstrate how to implement and utilize RetryableStatusCodeException. Below, we have a Spring Boot application where we define a RetryableResponseErrorHandler class that checks if an exception should be considered retryable:

public class RetryableResponseErrorHandler implements ResponseErrorHandler {

    @Override
    public boolean hasError(ClientHttpResponse response) throws IOException {
        return HttpStatus.Series.CLIENT_ERROR.equals(response.getStatusCode().series())
                || HttpStatus.Series.SERVER_ERROR.equals(response.getStatusCode().series());
    }

    @Override
    public void handleError(ClientHttpResponse response) throws IOException {
        if (HttpStatus.Series.SERVER_ERROR.equals(response.getStatusCode().series())) {
            throw new RetryableStatusCodeException("Server error occurred. Retry later.", response.getRawStatusCode());
        } else if (HttpStatus.Series.CLIENT_ERROR.equals(response.getStatusCode().series())) {
            throw new NonRetryableStatusCodeException("Client error occurred. Do not retry.", response.getRawStatusCode());
        }
    }
}

In the above code snippet, we define a custom RetryableResponseErrorHandler that implements the ResponseErrorHandler interface provided by Spring.

In the hasError() method, we check if the HTTP response indicates a client or server error. Based on this, we decide whether a retry is possible or not. If an error is classified as server-related, we throw a RetryableStatusCodeException, indicating that the request should be retried later.

In case of client-related errors, we can throw a different exception if we want to explicitly avoid any retries, such as a NonRetryableStatusCodeException.

To enable the automatic retry mechanism using RetryableStatusCodeException, we need to configure our RestTemplate bean accordingly:

@Configuration
public class RestTemplateConfig {

    @Bean
    public RestTemplate restTemplate() {
        RestTemplate restTemplate = new RestTemplate();

        restTemplate.setErrorHandler(new RetryableResponseErrorHandler());

        return restTemplate;
    }
}

In the RestTemplateConfig class, we define a restTemplate bean and register our custom RetryableResponseErrorHandler using the setErrorHandler() method. Now, any HTTP request made with this RestTemplate instance will automatically retry requests that result in retryable status codes.

5. Conclusion

Retrying HTTP requests in response to temporary errors is a necessary feature in robust web applications. By utilizing the RetryableStatusCodeException provided by the Spring framework, we can easily implement automatic retry mechanisms, ensuring application resilience in the face of transient failures.

In this article, we explored the RetryableStatusCodeException class and learned how to configure and utilize it effectively within a Spring application. By providing code examples and step-by-step instructions, we have hopefully clarified the implementation process and shown the convenience and practicality of this Spring feature.

Remember, having a robust error handling strategy is essential to any production application. By leveraging RetryableStatusCodeException, you can minimize user disruption caused by temporary network or server glitches, leading to a better user experience overall.

6. References

• Spring Web Module Documentation
• RestTemplate Documentation
• HTTP Status Codes - MDN Web Docs
• Meaning of Retryable Status Codes - Wikipedia

Happy coding!