<!DOCTYPE html>
< html lang = "en" >
< head >
< meta charset = "UTF-8" >
<!-- [if IE]><meta http - equiv="X - UA - Compatible" content="IE=edge"><![endif] -->
< meta name = "viewport" content = "width=device-width, initial-scale=1.0" >
< meta name = "generator" content = "Asciidoctor 1.5.8" >
< title > Introduction< / title >
< link rel = "stylesheet" href = "css/spring.css" >
< link rel = "stylesheet" href = "https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css" >
< style >
.hidden {
display: none;
}
.switch {
border-width: 1px 1px 0 1px;
border-style: solid;
border-color: #7a2518;
display: inline-block;
}
.switch--item {
padding: 10px;
background-color: #ffffff;
color: #7a2518;
display: inline-block;
cursor: pointer;
}
.switch--item:not(:first-child) {
border-width: 0 0 0 1px;
border-style: solid;
border-color: #7a2518;
}
.switch--item.selected {
background-color: #7a2519;
color: #ffffff;
}
< / style >
< script src = "https://cdnjs.cloudflare.com/ajax/libs/zepto/1.2.0/zepto.min.js" > < / script >
< script type = "text/javascript" >
function addBlockSwitches() {
$('.primary').each(function() {
primary = $(this);
createSwitchItem(primary, createBlockSwitch(primary)).item.addClass("selected");
primary.children('.title').remove();
});
$('.secondary').each(function(idx, node) {
secondary = $(node);
primary = findPrimary(secondary);
switchItem = createSwitchItem(secondary, primary.children('.switch'));
switchItem.content.addClass('hidden');
findPrimary(secondary).append(switchItem.content);
secondary.remove();
});
}
function createBlockSwitch(primary) {
blockSwitch = $('< div class = "switch" > < / div > ');
primary.prepend(blockSwitch);
return blockSwitch;
}
function findPrimary(secondary) {
candidate = secondary.prev();
while (!candidate.is('.primary')) {
candidate = candidate.prev();
}
return candidate;
}
function createSwitchItem(block, blockSwitch) {
blockName = block.children('.title').text();
content = block.children('.content').first().append(block.next('.colist'));
item = $('< div class = "switch--item" > ' + blockName + '< / div > ');
item.on('click', '', content, function(e) {
$(this).addClass('selected');
$(this).siblings().removeClass('selected');
e.data.siblings('.content').addClass('hidden');
e.data.removeClass('hidden');
});
blockSwitch.append(item);
return {'item': item, 'content': content};
}
$(addBlockSwitches);
< / script >
< / head >
< body class = "book toc2 toc-left" >
< div id = "header" >
< div id = "toc" class = "toc2" >
< div id = "toctitle" > Table of Contents< / div >
< ul class = "sectlevel1" >
< li > < a href = "#_introduction" > Introduction< / a >
< ul class = "sectlevel2" >
< li > < a href = "#_supported_implementations" > Supported Implementations< / a > < / li >
< / ul >
< / li >
< li > < a href = "#_core_concepts" > Core Concepts< / a >
< ul class = "sectlevel2" >
< li > < a href = "#_circuit_breakers_in_reactive_code" > Circuit Breakers In Reactive Code< / a > < / li >
< / ul >
< / li >
< li > < a href = "#_configuration" > Configuration< / a > < / li >
< / ul >
< / div >
< / div >
< div id = "content" >
< div class = "sect1" >
< h2 id = "_introduction" > < a class = "link" href = "#_introduction" > Introduction< / a > < / h2 >
< div class = "sectionbody" >
< div class = "paragraph" >
< p > Spring Cloud Circuit breaker provides an abstraction across different circuit breaker implementations.
It provides a consistent API to use in your applications, letting you, the developer, choose the circuit breaker implementation that best fits your needs for your application.< / p >
< / div >
< div class = "sect2" >
< h3 id = "_supported_implementations" > < a class = "link" href = "#_supported_implementations" > Supported Implementations< / a > < / h3 >
< div class = "paragraph" >
< p > Spring Cloud supports the following circuit-breaker implementations:< / p >
< / div >
< div class = "ulist" >
< ul >
< li >
< p > < a href = "https://github.com/Netflix/Hystrix" > Netflix Hystrix< / a > < / p >
< / li >
< li >
< p > < a href = "https://github.com/resilience4j/resilience4j" > Resilience4J< / a > < / p >
< / li >
< li >
< p > < a href = "https://github.com/alibaba/Sentinel" > Sentinel< / a > < / p >
< / li >
< li >
< p > < a href = "https://github.com/spring-projects/spring-retry" > Spring Retry< / a > < / p >
< / li >
< / ul >
< / div >
< / div >
< / div >
< / div >
< div class = "sect1" >
< h2 id = "_core_concepts" > < a class = "link" href = "#_core_concepts" > Core Concepts< / a > < / h2 >
< div class = "sectionbody" >
< div class = "paragraph" >
< p > To create a circuit breaker in your code, you can use the < code > CircuitBreakerFactory< / code > API. When you include a Spring Cloud Circuit Breaker starter on your classpath, a bean that implements this API is automatically created for you.
The following example shows a simple example of how to use this API:< / p >
< / div >
< div class = "exampleblock" >
< div class = "content" >
< div class = "listingblock" >
< div class = "content" >
< pre class = "highlightjs highlight" > < code class = "language-java hljs" data-lang = "java" > @Service
public static class DemoControllerService {
private RestTemplate rest;
private CircuitBreakerFactory cbFactory;
public DemoControllerService(RestTemplate rest, CircuitBreakerFactory cbFactory) {
this.rest = rest;
this.cbFactory = cbFactory;
}
public String slow() {
return cbFactory.create("slow").run(() -> rest.getForObject("/slow", String.class), throwable -> "fallback");
}
}< / code > < / pre >
< / div >
< / div >
< / div >
< / div >
< div class = "paragraph" >
< p > The < code > CircuitBreakerFactory.create< / code > API creates an instance of a class called < code > CircuitBreaker< / code > .
The < code > run< / code > method takes a < code > Supplier< / code > and a < code > Function< / code > .
The < code > Supplier< / code > is the code that you are going to wrap in a circuit breaker.
The < code > Function< / code > is the fallback that is executed if the circuit breaker is tripped.
The function is passed the < code > Throwable< / code > that caused the fallback to be triggered.
You can optionally exclude the fallback if you do not want to provide one.< / p >
< / div >
< div class = "sect2" >
< h3 id = "_circuit_breakers_in_reactive_code" > < a class = "link" href = "#_circuit_breakers_in_reactive_code" > Circuit Breakers In Reactive Code< / a > < / h3 >
< div class = "paragraph" >
< p > If Project Reactor is on the class path, you can also use < code > ReactiveCircuitBreakerFactory< / code > for your reactive code.
The following example shows how to do so:< / p >
< / div >
< div class = "exampleblock" >
< div class = "content" >
< div class = "listingblock" >
< div class = "content" >
< pre class = "highlightjs highlight" > < code class = "language-java hljs" data-lang = "java" > @Service
public static class DemoControllerService {
private ReactiveCircuitBreakerFactory cbFactory;
private WebClient webClient;
public DemoControllerService(WebClient webClient, ReactiveCircuitBreakerFactory cbFactory) {
this.webClient = webClient;
this.cbFactory = cbFactory;
}
public Mono< String> slow() {
return webClient.get().uri("/slow").retrieve().bodyToMono(String.class).transform(
it -> cbFactory.create("slow").run(it, throwable -> return Mono.just("fallback")));
}
}< / code > < / pre >
< / div >
< / div >
< / div >
< / div >
< div class = "paragraph" >
< p > The < code > ReactiveCircuitBreakerFactory.create< / code > API creates an instance of a class called < code > ReactiveCircuitBreaker< / code > .
The < code > run< / code > method takes a < code > Mono< / code > or a < code > Flux< / code > and wraps it in a circuit breaker.
You can optionally profile a fallback < code > Function< / code > , which will be called if the circuit breaker is tripped and is passed the < code > Throwable< / code >
that caused the failure.< / p >
< / div >
< / div >
< / div >
< / div >
< div class = "sect1" >
< h2 id = "_configuration" > < a class = "link" href = "#_configuration" > Configuration< / a > < / h2 >
< div class = "sectionbody" >
< div class = "paragraph" >
< p > You can configure your circuit breakers by creating beans of type < code > Customizer< / code > .
The < code > Customizer< / code > interface has a single method (called < code > customize< / code > ) that takes the < code > Object< / code > to customize.< / p >
< / div >
< div class = "paragraph" >
< p > For detailed information on how to customize a given implementation see
the following documentation:< / p >
< / div >
< div class = "ulist" >
< ul >
< li >
< p > < a href = "../../../../spring-cloud-netflix/current/reference/html/#circuit-breaker-spring-cloud-circuit-breaker-with-hystrix" > Hystrix< / a > < / p >
< / li >
< li >
< p > < a href = "../../../../spring-cloud-circuitbreaker/current/reference/html/spring-cloud-circuitbreaker.html#configuring-resilience4j-circuit-breakers" > Resilience4J< / a > < / p >
< / li >
< li >
< p > < a href = "https://github.com/alibaba/spring-cloud-alibaba/blob/master/spring-cloud-alibaba-docs/src/main/asciidoc/circuitbreaker-sentinel.adoc#circuit-breaker-spring-cloud-circuit-breaker-with-sentinel—​configuring-sentinel-circuit-breakers" > Sentinal< / a > < / p >
< / li >
< li >
< p > < a href = "../../../../spring-cloud-circuitbreaker/current/reference/html/spring-cloud-circuitbreaker.html#configuring-spring-retry-circuit-breakers" > Spring Retry< / a > < / p >
< / li >
< / ul >
< / div >
< div class = "paragraph" >
< p > Some < code > CircuitBreaker< / code > implementations such as < code > Resilience4JCircuitBreaker< / code > call < code > customize< / code > method every time < code > CircuitBreaker#run< / code > is called.
It can be inefficient. In that case, you can use < code > CircuitBreaker#once< / code > method. It is useful where calling < code > customize< / code > many times doesn’ t make sense,
for example, in case of < a href = "https://resilience4j.readme.io/docs/circuitbreaker#section-consume-emitted-circuitbreakerevents" > consuming Resilience4j’ s events< / a > .< / p >
< / div >
< div class = "paragraph" >
< p > The following example shows the way for each < code > io.github.resilience4j.circuitbreaker.CircuitBreaker< / code > to consume events.< / p >
< / div >
< div class = "exampleblock" >
< div class = "content" >
< div class = "listingblock" >
< div class = "content" >
< pre class = "highlightjs highlight" > < code class = "language-java hljs" data-lang = "java" > Customizer.once(circuitBreaker -> {
circuitBreaker.getEventPublisher()
.onStateTransition(event -> log.info("{}: {}", event.getCircuitBreakerName(), event.getStateTransition()));
}, CircuitBreaker::getName)< / code > < / pre >
< / div >
< / div >
< / div >
< / div >
< / div >
< / div >
< / div >
< script type = "text/javascript" src = "js/tocbot/tocbot.min.js" > < / script >
< script type = "text/javascript" src = "js/toc.js" > < / script >
< link rel = "stylesheet" href = "js/highlight/styles/atom-one-dark-reasonable.min.css" >
< script src = "js/highlight/highlight.min.js" > < / script >
< script > hljs . initHighlighting ( ) < / script >
< / body >
< / html >
