07: Spring Cloud with Resilience4j CircuitBreaker

Q. What is Resilience4j?
A. Resilience4j is a fault-tolerance library implementing the Circuit Breaker pattern inspired by Netflix Hystrix, but offers a more convenient API and a number of other features like Rate Limiter to block too many frequent requests to some services, Bulkhead to limit the number of concurrent requests to a specific service, cacheing, fail retry, and time limiter.

Step 1: Go to https://start.spring.io/ to create a skeleton project for a REST web service with Resilience4j.

Spring with Resilience4j

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Click on “generate” to download the “circuit-breaker-se.zip” file.

Step 2: Unzip “circuit-breaker-se.zip” inside the “projects folder” and open this folder with your IDE of your choice. I am opening the with “Visual Studio Code” IDE.

Step 3: The pom.xml file.

Step 4: Create a new folder “service” under “com/example/circuitbreakerse” in “src/main/java“.


Simulates a failing condition by sending a “NullPointerException” when no “name” is passed.

Step 5: Create a new folder “controller” under “com/example/circuitbreakerse” in “src/main/java“.


REST Web service with CircuitBreaker.

Step 6: The main bootstrap class in “com/example/circuitbreakerse” under “src/main/java“.


Step 7: Build the jar and run it.


Step 8: Open a web browser.

URL: http://localhost:8080/hello?name=John
Output: Hello John!

CircuitBreaker in action when no “name” parameter is supplied.

URL: http://localhost:8080/hello
Output: Hello NoName

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