111 lines
4.0 KiB
Markdown
111 lines
4.0 KiB
Markdown
# CircuitBreaker
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resilience4j是一个轻量级的fault tolerance library，其针对函数式编程进行设计。resilence4j提供了更高阶的函数（`decorator`）来对`function interface, lambda expression, method reference`等内容进行增强。
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decorators包含如下分类：
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- CircuitBreaker
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- Rate Limiter
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- Retry
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- Bulkhead
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对于任何`function interface, lambda expression, method reference`，都可以使用多个decorators进行装饰。
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## Introduction
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在如下示例中，会展示如何通过CircuitBreaker和Retry来对lambda expression进行装饰，令lambda在发生异常时最多重试3次。
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可以针对多次retry之间的interval进行配置，也支持自定义的backoff algorithm。
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```java
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// Create a CircuitBreaker with default configuration
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CircuitBreaker circuitBreaker = CircuitBreaker
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.ofDefaults("backendService");
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// Create a Retry with default configuration
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// 3 retry attempts and a fixed time interval between retries of 500ms
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Retry retry = Retry
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.ofDefaults("backendService");
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// Create a Bulkhead with default configuration
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Bulkhead bulkhead = Bulkhead
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.ofDefaults("backendService");
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Supplier<String> supplier = () -> backendService
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.doSomething(param1, param2)
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// Decorate your call to backendService.doSomething()
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// with a Bulkhead, CircuitBreaker and Retry
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// **note: you will need the resilience4j-all dependency for this
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Supplier<String> decoratedSupplier = Decorators.ofSupplier(supplier)
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.withCircuitBreaker(circuitBreaker)
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.withBulkhead(bulkhead)
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.withRetry(retry)
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.decorate();
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// When you don't want to decorate your lambda expression,
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// but just execute it and protect the call by a CircuitBreaker.
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String result = circuitBreaker
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.executeSupplier(backendService::doSomething);
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// You can also run the supplier asynchronously in a ThreadPoolBulkhead
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ThreadPoolBulkhead threadPoolBulkhead = ThreadPoolBulkhead
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.ofDefaults("backendService");
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// The Scheduler is needed to schedule a timeout
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// on a non-blocking CompletableFuture
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ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(3);
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TimeLimiter timeLimiter = TimeLimiter.of(Duration.ofSeconds(1));
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CompletableFuture<String> future = Decorators.ofSupplier(supplier)
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.withThreadPoolBulkhead(threadPoolBulkhead)
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.withTimeLimiter(timeLimiter, scheduledExecutorService)
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.withCircuitBreaker(circuitBreaker)
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.withFallback(asList(TimeoutException.class,
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CallNotPermittedException.class,
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BulkheadFullException.class),
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throwable -> "Hello from Recovery")
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.get().toCompletableFuture();
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```
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## maven
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resilence4j需要jdk17及以上，如果使用maven，可以按照如下方式来引入
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引入所有包的方式如下
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```xml
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-all</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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```
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按需引入方式如下
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```xml
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-circuitbreaker</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-ratelimiter</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-retry</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-bulkhead</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-cache</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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<dependency>
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<groupId>io.github.resilience4j</groupId>
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<artifactId>resilience4j-timelimiter</artifactId>
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<version>${resilience4jVersion}</version>
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</dependency>
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``` |