Spring Boot provides a convenient way to implement the circuit breaker pattern in your application using the Resilience4j library. Here's an example of how you can use it:

1. First, add the resilience4j-spring-boot2 dependency to your project:

<dependency>
    <groupId>io.github.resilience4j</groupId>
    <artifactId>resilience4j-spring-boot2</artifactId>
    <version>{resilience4j-version}</version>
</dependency>

1. Next, define a circuit breaker configuration in your application's configuration file (e.g. application.yml):

resilience4j:
  circuitbreaker:
    configs:
      myService:
        registerHealthIndicator: true
        failureRateThreshold: 50
        waitDurationInOpenState: 5s
        ringBufferSizeInHalfOpenState: 2
        ringBufferSizeInClosedState: 2

This configuration specifies that the circuit breaker for myService should open if the failure rate exceeds 50% and remain open for 5 seconds before transitioning to half-open state. The circuit breaker will use a sliding window of size 2 to track failures and successes in both the closed and half-open states.

1. Now you can use the CircuitBreaker API in your code to wrap your service calls and apply the circuit breaker pattern. For example:

@Service
public class MyService {

    private final CircuitBreaker circuitBreaker;

    public MyService(CircuitBreakerRegistry circuitBreakerRegistry) {
        this.circuitBreaker = circuitBreakerRegistry.circuitBreaker("myService");
    }

    public String doSomething() {
        return circuitBreaker.executeSupplier(this::callService);
    }

    private String callService() {
        // call service and return result
    }
}

The executeSupplier method wraps the callService method with the circuit breaker logic. If the circuit breaker is open, the executeSupplier method will throw a CircuitBreakerOpenException without calling the service. If the circuit breaker is closed, the executeSupplier method will call the service and record the result (success or failure). If the circuit breaker is half-open, the executeSupplier method will call the service and record the result, and the circuit breaker will transition to either the open or closed state based on the result.

You can also use the CircuitBreaker API to decorate methods with the @CircuitBreaker annotation, like this:

@Service
public class MyService {

    @CircuitBreaker(name = "myService")
    public String doSomething() {
        // call service and return result
    }
}

This will automatically apply the circuit breaker pattern to the doSomething method using the myService the configuration defined in the application's configuration file.

how to handle the fallback scenario

To handle the fallback scenario when the circuit breaker is open, you can use the CircuitBreaker API's withFallback method. For example:

@Service
public class MyService {

    private final CircuitBreaker circuitBreaker;

    public MyService(CircuitBreakerRegistry circuitBreakerRegistry) {
        this.circuitBreaker = circuitBreakerRegistry.circuitBreaker("myService");
    }

    public String doSomething() {
        return circuitBreaker.executeSupplier(this::callService)
                             .withFallback(this::fallback);
    }

    private String callService() {
        // call service and return result
    }

    private String fallback() {
        // return fallback result
    }
}

The withFallback method specifies a fallback supplier to be called if the circuit breaker is open or if the wrapped service call throws an exception. The fallback supplier should return a result or throw an exception.

You can also use the Fallback API to specify fallback logic for a method annotated with @CircuitBreaker, like this:

@Service
public class MyService {

    @CircuitBreaker(name = "myService", fallbackMethod = "fallback")
    public String doSomething() {
        // call service and return result
    }

    public String fallback() {
        // return fallback result
    }
}

In this case, the fallback method will be called if the circuit breaker is open or if the doSomething method throws an exception.

I hope this helps! Let me know if you have any questions.

how parameter information will pass to fallback method

If you want to pass parameter information to the fallback method, you can use method arguments and return the appropriate result based on the arguments. For example:

@Service
public class MyService {

    private final CircuitBreaker circuitBreaker;

    public MyService(CircuitBreakerRegistry circuitBreakerRegistry) {
        this.circuitBreaker = circuitBreakerRegistry.circuitBreaker("myService");
    }

    public String doSomething(String input) {
        return circuitBreaker.executeSupplier(() -> callService(input))
                             .withFallback(ex -> fallback(input, ex));
    }

    private String callService(String input) {
        // call service and return result
    }

    private String fallback(String input, Throwable ex) {
        // return fallback result based on the input and exception
    }
}

In this example, the doSomething method passes the input parameter to both the service call and the fallback method. The fallback method also receives the ex parameter, which is the exception thrown by the service call. You can use these parameters to return the appropriate fallback result based on the input and the exception.

If you are using the @CircuitBreaker annotation with a fallback method, you can pass parameter information in the same way:

@Service
public class MyService {

    @CircuitBreaker(name = "myService", fallbackMethod = "fallback")
    public String doSomething(String input) {
        // call service and return result
    }

    public String fallback(String input, Throwable ex) {
        // return fallback result based on the input and exception
    }
}

I hope this helps!

Thanks For Reading