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Learn how to catch exceptions thrown by `WebClient` in `Spring Boot` applications and handle them using a global error handler for a responsive microservice architecture.
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Resolving Spring Boot Exceptions in WebClient: Enforcing Global Error Handling

In modern microservices architecture, Spring Boot has become a go-to framework for building robust applications. One common challenge developers face is effectively handling exceptions that arise when using WebClient, especially when invoking remote services. This challenge includes ensuring that exceptions thrown during reactive streams in your application are appropriately caught and managed.

In this guide, we’ll explore how to resolve issues related to exceptions in WebClient when using reactive programming, specifically when those exceptions do not get caught by typical exception handling strategies, such as @ControllerAdvice.

The Problem: Uncaught Exceptions in WebClient

When invoking services via WebClient, exceptions might occur due to various reasons, such as token validation failures or connectivity issues. For instance, let’s consider a scenario:

You are implementing an AuthFilter component that validates JWT tokens against a microservice (let's call it “uaa”). If the token validation fails, an exception is thrown. However, you notice that the exception is not caught in your global exception handler (ExceptionController).

Here’s a snippet of the AuthFilter code where the exception is thrown:

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Why This Happens

The core of the issue lies in the behavior of Mono and Flux objects in a reactive context. Exceptions in such methods do not propagate normally to the @ExceptionHandler annotated classes because they operate asynchronously. Therefore, a different approach is required to handle these exceptions.

The Solution: Implementing a Global Error Handler

To effectively manage exceptions thrown from your WebClient calls, we need to extend AbstractErrorWebExceptionHandler, allowing us to provide a global error handling strategy for our application. Below are detailed steps to implement this solution.

Step 1: Create a Global Error Handler

Start by creating a class that extends AbstractErrorWebExceptionHandler. This class will handle errors in a reactive manner.

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Step 2: Define Custom Error Attributes

You need to specify what details should be included in the error response. Creating a class for custom error attributes can be done as follows:

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Step 3: Error Response Structure

Finally, design the response structure according to your application needs, ensuring all relevant error info is presented in a friendly format.

Conclusion

By following these steps, you can effectively handle exceptions thrown by WebClient in your Spring Boot applications. Adopting a global error handler approach ensures a standardized error management process across your microservices and allows you to maintain consistent responses, which is vital for the overall user experience.

Now, whenever you encounter exceptions from WebClient, they will be handled gracefully, improving the resilience of your microservices.

For more patterns and practices in dealing with exceptions in reactive programming, stay tuned for our upcoming posts!