How to Route Error Responses and HTTP Status Using Spring WebClient

Learn how to properly route error responses and HTTP status codes in Spring WebClient while maintaining the integrity of your response in a Spring Boot application.
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Routing Error Responses and HTTP Status with Spring WebClient

When working with RESTful applications in Spring Boot, it's common to face challenges related to handling error responses, particularly when using the WebClient. This can be especially cumbersome when trying to ensure that both the body and HTTP status from one application (BusinessApp) are accurately routed through another application (ProxyApp). In this post, we’ll explore a solution to this problem, breaking it down into clear and understandable steps.

Understanding the Problem

In our scenario, we have two Spring Boot applications:

ProxyApp: This acts as a middleman, handling requests from an Angular frontend and wrapping the API calls made to the BusinessApp.

BusinessApp: This one contains the business logic and returns either a successful response (200 OK) or an error response (like a 400 Bad Request) through the use of @ ControllerAdvice.

When ProxyApp calls the BusinessApp using the Spring WebClient, we run into an issue: the HTTP status returned by BusinessApp is being reset to 200 OK, even when an error occurs. This behavior can lead to confusion and makes debugging much harder.

The Root Cause

The issue arises from the following line in your WebClient usage:

[[See Video to Reveal this Text or Code Snippet]]

The Solution

To address this issue, we need to refine our WebClient error handling. Here’s how:

Remove the onStatus() Method

First, we need to remove the .onStatus() method call from our WebClient code. The modified code should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Create an Exception Handler

Next, we need to create an exception handler that will catch the WebClientResponseException. This exception contains vital details about what went wrong, including the status code and the response body. Here is how you can implement this in your application:

[[See Video to Reveal this Text or Code Snippet]]

This error handler will ensure that when a WebClientResponseException is thrown, the response will contain the correct status code along with the error message returned from the BusinessApp.

Additional Notes

Reactive Benefits: It’s worth mentioning that using .block() in your reactive stack is generally discouraged as it stops the reactive flow. Consider redesigning your code to avoid blocking, leveraging the full potential of the reactive programming paradigm.

Keep Testing: After making these changes, make sure to test your application thoroughly. Confirm that error responses from BusinessApp are now clearly routed through ProxyApp with the appropriate status codes.

Conclusion

Handling error responses and HTTP status codes in a Spring WebClient setup can initially seem daunting, but by implementing the steps outlined in this guide, you can route both the body and the status code from one Spring Boot application to another seamlessly. Follow these best practices, and you'll enhance the reliability and usability of your microservices.

Whether you’re developing a new app or maintaining an existing setup, understanding the nuances of error handling can save you a lot of headaches down the road.