Examples

Examples of resilience4j-circuitbreaker

Create a CircuitBreakerRegistry

Create a CircuitBreakerRegistry with a custom CircuitBreakerConfig.

Java

// Create a custom configuration for a CircuitBreaker
CircuitBreakerConfig circuitBreakerConfig = CircuitBreakerConfig.custom()
    .failureRateThreshold(50)
    .waitDurationInOpenState(Duration.ofMillis(1000))
    .ringBufferSizeInHalfOpenState(2)
    .ringBufferSizeInClosedState(2)
    .recordExceptions(IOException.class, TimeoutException.class)
    .ignoreExceptions(BusinessException.class, OtherBusinessException.class)
    .build();

// Create a CircuitBreakerRegistry with a custom global configuration
CircuitBreakerRegistry circuitBreakerRegistry =
  CircuitBreakerRegistry.of(circuitBreakerConfig);

Create a CircuitBreaker

Get a CircuitBreaker from the CircuitBreakerRegistry with the global default configuration

Java

CircuitBreaker circuitBreaker = circuitBreakerRegistry
  .circuitBreaker("name");

Decorate a functional interface

Decorate your call to BackendService.doSomething() with a CircuitBreaker and execute the decorated supplier and recover from any exception.

Java

Supplier<String> decoratedSupplier = CircuitBreaker
    .decorateSupplier(circuitBreaker, backendService::doSomething);

String result = Try.ofSupplier(decoratedSupplier)
    .recover(throwable -> "Hello from Recovery").get();

Execute a decorated functional interface

When you don't want to decorate your lambda expression, but just execute it and protect the call by a CircuitBreaker.

Java

String result = circuitBreaker
  .executeSupplier(backendService::doSomething);

Recover from an exception

If you want to recover from an exception after the CircuitBreaker recorded it as a failure, you can chain the method Try.recover(). The recovery method is only invoked, if Try.of() returns a Failure<Throwable> Monad.

Java

// Given
CircuitBreaker circuitBreaker = CircuitBreaker.ofDefaults("testName");

// When I decorate my function and invoke the decorated function
CheckedFunction0<String> checkedSupplier =
  CircuitBreaker.decorateCheckedSupplier(circuitBreaker, () -> {
    throw new RuntimeException("BAM!");
});
Try<String> result = Try.of(checkedSupplier)
        .recover(throwable -> "Hello Recovery");

// Then the function should be a success, 
// because the exception could be recovered
assertThat(result.isSuccess()).isTrue();
// and the result must match the result of the recovery function.
assertThat(result.get()).isEqualTo("Hello Recovery");

If you want to recover from an exception before the CircuitBreaker records it as a failure, you can do the following:

Java

Supplier<String> supplier = () -> {
            throw new RuntimeException("BAM!");
        };

Supplier<String> supplierWithRecovery = SupplierUtils
  .recover(supplier, (exception) -> "Hello Recovery");

String result = circuitBreaker.executeSupplier(supplierWithRecovery);

assertThat(result).isEqualTo("Hello Recovery");

SupplierUtils and CallableUtils contain other methods like andThen which can take can be used to chain functions. For example to check the status code of a HTTP response, so that exceptions can be thrown.

Java

Supplier<String> supplierWithResultAndExceptionHandler = SupplierUtils
  .andThen(supplier, (result, exception) -> "Hello Recovery");

Supplier<HttpResponse> supplier = () -> httpClient.doRemoteCall();
Supplier<String> supplierWithResultHandling = SupplierUtils.andThen(supplier, result -> {
    if (result.getStatusCode() == 400) {
       throw new ClientException();
    } else if (result.getStatusCode() == 500) {
       throw new ServerException();
    });
HttpResponse httpResponse = circuitBreaker
  .executeSupplier(supplierWithResultHandling);

Reset CircuitBreaker

The Circuit Breaker supports resetting to its original state, losing all the metrics and effectively resetting its Ring Bit Buffer.

Java

CircuitBreaker circuitBreaker = CircuitBreaker.ofDefaults("testName");
circuitBreaker.reset();

Transition to states manually

Java

CircuitBreaker circuitBreaker = CircuitBreaker.ofDefaults("testName");
circuitBreaker.transitionToDisabledState();
// circuitBreaker.onFailure(...) won't trigger a state change
circuitBreaker.transitionToClosedState(); // will transition to CLOSED state and re-enable normal behaviour, keeping metrics
circuitBreaker.transitionToForcedOpenState();
// circuitBreaker.onSuccess(...) won't trigger a state change
circuitBreaker.reset(); //  will transition to CLOSED state and re-enable normal behaviour, losing metrics