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Discover how to wait for Mono completion in Spring WebClient, allowing you to effectively utilize the generated values in your applications.
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How to Properly Wait for Mono Completion in Spring WebClient

When working with reactive programming in Kotlin, especially with frameworks like Spring WebFlux, developers often encounter the challenge of managing asynchronous operations. One common question that arises is how to effectively wait for a Mono to complete so that the generated value can be utilized. In this post, we'll tackle this issue by providing a clear solution.

The Problem: Waiting for Mono Completion

In your scenario, you want to return the HTTP status code from the sendRequest() method rather than merely printing it. You are right to avoid using Thread.sleep(1000); as it's not a viable solution in reactive programming; it blocks the thread and defeats the purpose of non-blocking I/O.

You're using Spring's WebClient, which works with the reactive streams paradigm, meaning you need to manage subscriptions properly. The challenge is to return the Mono to the caller and ensure they can subscribe to it for the desired results.

The Solution: Modify the sendRequest Method

To modify your sendRequest() method to effectively wait for the Mono to complete and return the result, follow these steps:

Step 1: Change the return type

Modify your sendRequest() method to return a Mono<HttpStatus> instead of a Disposable. This allows the caller to manage the subscription directly.

Step 2: Return the Mono

Change the invocation of the exchange() method to directly map the response and return the resulting Mono<HttpStatus>:

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Step 3: Subscribe to the Mono

Now that your method correctly returns a Mono<HttpStatus>, you can call this method elsewhere in your code and subscribe to it to get the status:

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

Step 4: Print the Status

The printStatus function remains the same. You simply pass the received HttpStatus directly to it:

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

Conclusion

By restructuring your sendRequest() method to return a Mono<HttpStatus>, you align more closely with reactive principles and allow the calling code to handle the response asynchronously. This ensures that you're not blocking any threads, thus maintaining the efficiency of your application.

If you want to effectively manage asynchronous operations in your Spring WebFlux application, remember that returning Mono or Flux is key to letting the calling client subscribe and react to results.

Feel free to implement these changes in your code, and enjoy the benefits of clean, efficient, non-blocking HTTP communications!