How to Make Simultaneous REST API Calls Using FeignClient in Spring Boot

Learn how to efficiently handle `simultaneous REST API calls` in Spring Boot using Spring WebClient to improve performance and responsiveness in microservices.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Make Simultaneous Rest API calls using FeignClient in Spring Boot

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Handling Simultaneous REST API Calls in Spring Boot

In the world of microservices, efficient communication between services is crucial for maintaining performance and responsiveness. A common challenge developers face is the need for one microservice (Service A) to make multiple API calls to another microservice (Service B), especially when those calls are synchronous and can lead to increased latency. If you're using FeignClient to manage these API calls, you might wonder how to enhance performance by making those calls asynchronous. In this guide, we will explore the problem and provide a clear solution using Spring WebClient.

The Problem: Synchronous API Calls

Imagine you have two microservices:

Service A: The service that requests data.

Service B: The service that provides data in response to API calls.

When a request comes to Service A, it may need to query Service B multiple times, each with different parameters. The default behavior of FeignClient is to make these calls synchronously, meaning that Service A will wait for each response from Service B before proceeding to the next request. This can lead to significant delays, especially when multiple calls are involved.

Example Scenario:

Service A receives a request.

Service A makes a call to Service B for a specific parameter.

Service A waits for the response before making the next call to Service B with a different parameter.

This sequential process can become a bottleneck, impacting the overall user experience and system performance. So how can we tackle this problem?

The Solution: Using Spring WebClient

To solve the issue of synchronous API calls, we can leverage Spring WebClient, an asynchronous, non-blocking solution provided by the Spring Reactive framework. Spring WebClient enables concurrent execution of REST API calls, allowing Service A to fire off multiple requests simultaneously and wait for the responses without blocking.

What is Spring WebClient?

WebClient is a part of the Spring 5 framework and is designed for making HTTP requests in a non-blocking manner.

It allows for more control over HTTP interactions than its predecessor, RestTemplate, and is suitable for reactive programming.

How to Implement Simultaneous API Calls

Here's how you can implement simultaneous API calls using Spring WebClient:

Initiate Multiple Requests: Use WebClient to initiate multiple requests concurrently.

Example Code Snippet

Here's an example code snippet that demonstrates how to make simultaneous API calls using Spring WebClient:

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

Explanation of the Code:

request1() and request2() are methods that initiate calls to Service B with different parameters and return Mono<String> representing the response.

flatMap(result -> transformer(result)) processes the combined result asynchronously, allowing Service A to manage it efficiently.

Conclusion

By replacing synchronous calls with asynchronous calls using Spring WebClient, Service A can significantly reduce the latency associated with communicating with Service B. With the power of reactive programming, we can enhance the performance of our microservices architecture.

If you're currently facing issues with blocking calls in your microservices, consider migrating to WebClient for a more responsive and performant solution. Happy coding!