This is a very simple example spring boot project with implementation of circuit breaker pattern

Dependencies used:

-circutbreaker resilense4j(order-service)
-spring boot starter actuator(order-service)
-spring boot starter data jpa
-spring boot starter data web
-h2 database
-lombok

Some version specificated:

-Spring boot 3.2.4
-Java 17
-Maven (compile tool)

How works?

The address-service handle a collections data of address (code, state and city) this data is charged to H2 Dastabase locally through the setupData() method, marked with the $\color{#FFFF00}{@PostConstructor}$ anotation and these data are retrieved of (address-service) through of call to endpoint (using restTemplate) from order-service finally in the purchase simulation, the order-service will accessed by the customer when send in the endpoint call the postal code.

How test the circuit breaker implementation?

You can access to "http://localhost:9091/actuator/health" and in this point you should can view the circuit breaker status (in order-service) the circuit breker status "UP" and the service status will be "CLOSED" (order-service) this case is when both services is running normally (ideal scenario), but when the address-service failed or this service is down, these values will change to "UNKNOWN" and "OPEN" respectively this behavior will because the circuit breaker is active and after some second (values configurated in application.yml file of service where circuit breaker pattern was configured) in our case these service is order-service . All time while our order-service will be down or not responding correctly the circuit breaker status will be "HALF_OPEN" (this means that the called to address-services works apparently fine, but behind the scene our fallback method implemented as a option to circuit breaker will be working and responding our data, and in this point you will knows because both object of response implemented the same interface "type" is basically becausse give a strong type) finally when the addres-services will be restablished and works fine (previous pushed to api) the values of circuit breaker in the /actuator/health endpoint changes once again to "UP" status.