doc: 阅读Retry文档
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asahi
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- [decorate and execute a functional interface](#decorate-and-execute-a-functional-interface-2)
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- [consume emitted RegistryEvents](#consume-emitted-registryevents-2)
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- [consume emitted RateLimiterEvents](#consume-emitted-ratelimiterevents)
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- [Retry](#retry)
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- [Create a RetryRegistry](#create-a-retryregistry)
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- [Create and configure Retry](#create-and-configure-retry)
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- [Decorate and execute a functional interface](#decorate-and-execute-a-functional-interface-3)
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- [consume emitted RegistryEvents](#consume-emitted-registryevents-3)
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- [use custom IntervalFunction](#use-custom-intervalfunction)
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# CircuitBreaker
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@@ -704,3 +710,155 @@ ReactorAdapter.toFlux(rateLimiter.getEventPublisher())
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.filter(event -> event.getEventType() == FAILED_ACQUIRE)
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.subscribe(event -> logger.info(...))
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```
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## Retry
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### Create a RetryRegistry
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和CircuitBreaker module类似，该module也提供了in-memory RetryRegistry，用于对Retry对象进行管理。
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```java
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RetryRegistry retryRegistry = RetryRegistry.ofDefaults();
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```
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### Create and configure Retry
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可以提供一个自定义的global RetryConfig，可以使用builder来创建RetryConfig。
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RetryConfig支持如下配置：
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- `maxAttempts`:
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- `default value`: 3
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- `description`：该参数代表最大尝试次数（包含最初始的调用，最初始的调用为first attemp）
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- `waitDuration`:
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- `default value`: 500 [ms]
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- `description`: 在多次retry attempts之间的固定等待间隔
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- `intervalFunction`:
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- `defaultValue`: `numOfAttempts -> waitDuration`
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- `description`: 该参数对应的function用于在失败后修改等待时间，默认情况下每次失败后等待时间是固定的，都是waitDuration
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- `intervalBiFunction`:
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- `default value`: `(int numOfAttempts, Either<Throwable, T> result)->waitDuration`
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- `description`: 该function用于在failure后修改等待时间间隔，即基于attempt number和result/exception来计算等待时间间隔。当同时使用`intervalFunction`和`intervalBiFunction`时，会抛出异常
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- `retryOnResultPredicate`：
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- `default value`: `result -> false`
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- `description`: 该参数用于配置predicate，用于判断result是否应该被重试。如果result应当被重试，那么返回true，否则返回false
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- `retryOnExceptionPredicate`:
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- `default`: `throwable -> true`
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- `description`: 该参数用于判断是否exception应当被重试。如果exception应当被重试，predicate返回true，否则返回false
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- `retryExceptions`：
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- `default value`: empty
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- `description`: 配置exception list，其将被记录为failure并且应当被重试。
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- `ignoreExceptions`:
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- `default value`: empty
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- `descritpion`: 配置exception list，该列表中的异常会被ignore并且不会重试
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- `failAfterMaxAttempts`:
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- `default value`: false
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- `description`: 该参数用于启用和关闭`MaxRetriesExceededException`的抛出，当Retry达到配置的maxAttempts后，若result没有通过`retryOnResultPredicate`，则会根据`failAfterMaxAttempts`来重试
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> 在抛出异常后，是否重试的逻辑如下：
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> - 根据predicate判断该异常是否应该重试，predicate逻辑判断流程如下
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> - 如果异常位于ignoreExceptions中，则不应重试
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> - 如果异常位于retryExceptions中，则predicate返回为true
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> - 如果异常不位于retryExceptions中，则根据retryOnExceptionPredicate来判断是否异常应当触发重试
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> - 如果上述的predicate判断异常应该被重试，那么再递增重试次数，判断当前重试是否超过maxAttempts
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> - 如果没有超过，则在等待interval后触发重试
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> - 如果超过maxAttempts规定的上限，则不再重试直接抛出异常
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> 在未抛出异常时，判断是否重试的逻辑如下：
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> - 首先，根据`retryOnResultPredicate`判断当前返回结果是否应当触发重试，如果不应触发重试，则流程结束
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> - 如果应当触发重试，则增加当前的重试次数，并和maxAttempts进行比较
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> - 如果当前重试次数未超过maxAttempts，则在等待interval后触发重试
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> - 如果重试次数超过maxAttempts规定的值，那么将根据failAfterMaxAttempts来决定是否抛出异常。当failAfterMaxAttempts为true时，抛出异常；当为false时，不跑出异常。默认不会抛出异常。
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创建RetryConfig的默认示例如下：
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```java
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RetryConfig config = RetryConfig.custom()
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.maxAttempts(2)
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.waitDuration(Duration.ofMillis(1000))
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.retryOnResult(response -> response.getStatus() == 500)
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.retryOnException(e -> e instanceof WebServiceException)
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.retryExceptions(IOException.class, TimeoutException.class)
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.ignoreExceptions(BusinessException.class, OtherBusinessException.class)
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.failAfterMaxAttempts(true)
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.build();
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// Create a RetryRegistry with a custom global configuration
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RetryRegistry registry = RetryRegistry.of(config);
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// Get or create a Retry from the registry -
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// Retry will be backed by the default config
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Retry retryWithDefaultConfig = registry.retry("name1");
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// Get or create a Retry from the registry,
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// use a custom configuration when creating the retry
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RetryConfig custom = RetryConfig.custom()
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.waitDuration(Duration.ofMillis(100))
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.build();
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Retry retryWithCustomConfig = registry.retry("name2", custom);
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```
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### Decorate and execute a functional interface
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Retry可以针对`callable, supplier, runnable, consumer, checkedrunnable, checkedsupplier, checkedconsumer, completionstage`进行decorate，使用示例如下：
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```java
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// Given I have a HelloWorldService which throws an exception
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HelloWorldService helloWorldService = mock(HelloWorldService.class);
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given(helloWorldService.sayHelloWorld())
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.willThrow(new WebServiceException("BAM!"));
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// Create a Retry with default configuration
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Retry retry = Retry.ofDefaults("id");
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// Decorate the invocation of the HelloWorldService
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CheckedFunction0<String> retryableSupplier = Retry
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.decorateCheckedSupplier(retry, helloWorldService::sayHelloWorld);
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// When I invoke the function
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Try<String> result = Try.of(retryableSupplier)
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.recover((throwable) -> "Hello world from recovery function");
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// Then the helloWorldService should be invoked 3 times
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BDDMockito.then(helloWorldService).should(times(3)).sayHelloWorld();
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// and the exception should be handled by the recovery function
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assertThat(result.get()).isEqualTo("Hello world from recovery function");
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```
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### consume emitted RegistryEvents
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可以向RetryRegistry注册监听，消费Retry的create, replace, delete事件
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```java
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RetryRegistry registry = RetryRegistry.ofDefaults();
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registry.getEventPublisher()
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.onEntryAdded(entryAddedEvent -> {
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Retry addedRetry = entryAddedEvent.getAddedEntry();
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LOG.info("Retry {} added", addedRetry.getName());
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})
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.onEntryRemoved(entryRemovedEvent -> {
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Retry removedRetry = entryRemovedEvent.getRemovedEntry();
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LOG.info("Retry {} removed", removedRetry.getName());
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});
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```
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### use custom IntervalFunction
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如果不想使用fixed wait duration，可以自定义`IntervalFunction`，该函数可以在每次attempt时独立计算wait duration。resilience4j支持一些工厂方法用于创建IntervalFunction，示例如下
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```java
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IntervalFunction defaultWaitInterval = IntervalFunction
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.ofDefaults();
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// This interval function is used internally
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// when you only configure waitDuration
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IntervalFunction fixedWaitInterval = IntervalFunction
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.of(Duration.ofSeconds(5));
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IntervalFunction intervalWithExponentialBackoff = IntervalFunction
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.ofExponentialBackoff();
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IntervalFunction intervalWithCustomExponentialBackoff = IntervalFunction
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.ofExponentialBackoff(IntervalFunction.DEFAULT_INITIAL_INTERVAL, 2d);
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IntervalFunction randomWaitInterval = IntervalFunction
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.ofRandomized();
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// Overwrite the default intervalFunction with your custom one
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RetryConfig retryConfig = RetryConfig.custom()
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.intervalFunction(intervalWithExponentialBackoff)
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.build();
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```
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> intervalFunction和intervalBiFunction不能同时指定，同时指定时会抛出异常。
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>
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> 如果指定了intervalFunction，那么在通过builder创建RetryConfig时，会自动通过intervalFunction给intervalBiFunction也赋值。
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>
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> 如果指定了intervalFunction或intervalBiFunction中任一，则使用指定的函数来计算waitDuration，当二者都没有指定时，则waitDuration固定为waitDuration
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