使用 Spring-Retry 指定特定於異常的退避策略

Question

我正在使用Spring-Retry進行一些數據庫操作。 在SQLRecoverableException我重試了 3 次（這假設導致異常的原因是非暫時性的，如果它失敗了 3 次），在SQLTransientException我無限期地重試（程序不能在沒有訪問數據庫的情況下做任何事情，所以它可能並繼續重試，直到用戶決定重新啟動服務器），並且在任何其他異常情況下我不會重試。 我使用指數退避策略，基本重試時間為 100 毫秒，最大重試時間為 30,000 毫秒。

private static final int MAX_RECOVERABLE_RETRIES = 3;
private static final long INITIAL_INTERVAL = 100;
private static final long MAX_INTERVAL = 30 * 1000;
private static final double MULTIPLIER = 2.0;

public static RetryTemplate databaseTemplate() {
    RetryTemplate template = new RetryTemplate();
    ExceptionClassifierRetryPolicy retryPolicy = new ExceptionClassifierRetryPolicy();
    Map<Class<? extends Throwable>, RetryPolicy> policyMap = new HashMap<>();
    NeverRetryPolicy baseException = new NeverRetryPolicy();
    SimpleRetryPolicy recoverablePolicy = new SimpleRetryPolicy();
    recoverablePolicy.setMaxAttempts(MAX_RECOVERABLE_RETRIES);
    AlwaysRetryPolicy transientPolicy = new AlwaysRetryPolicy();
    policyMap.put(Exception.class, baseException);
    policyMap.put(SQLRecoverableException.class, recoverablePolicy);
    policyMap.put(SQLTransientException.class, transientPolicy);
    retryPolicy.setPolicyMap(policyMap);
    template.setRetryPolicy(retryPolicy);
    ExponentialBackOffPolicy backOffPolicy = new ExponentialBackOffPolicy();
    backOffPolicy.setInitialInterval(INITIAL_INTERVAL);
    backOffPolicy.setMaxInterval(MAX_INTERVAL);
    backOffPolicy.setMultiplier(MULTIPLIER);
    template.setBackOffPolicy(backOffPolicy);
    return template;
}

理想情況下，我想對所有SQLRecoverableExceptions使用 100 毫秒的固定退避，並且只將指數退避策略應用於SQLTransientExceptions 。 我可以通過嵌套重試來實現這一點，但這會大大增加代碼的復雜性——如果沒有其他選擇，我寧願簡單地將指數退避應用於SQLRecoverableException和SQLTransientException異常。

有沒有辦法使用單個重試模板將不同的退避策略應用於不同的異常？

Answer 1

確實， ExceptionClassifierRetryPolicy是要走的路。 不過，我沒有設法讓它與policyMap一起使用。

這是我如何使用它：

@Component("yourRetryPolicy")
public class YourRetryPolicy extends ExceptionClassifierRetryPolicy
{
    @PostConstruct
    public void init()
    {
        final SimpleRetryPolicy simpleRetryPolicy = new SimpleRetryPolicy();
        simpleRetryPolicy.setMaxAttempts( 3 );

        this.setExceptionClassifier( new Classifier<Throwable, RetryPolicy>()
        {
            @Override
            public RetryPolicy classify( Throwable classifiable )
            {
                    if ( classifiable instanceof YourException )
                    {
                            return new NeverRetryPolicy();
                    }
                    // etc...
                    return simpleRetryPolicy;
            }
        });
    }
}

然后，您只需在重試模板上設置它：

@Autowired
@Qualifier("yourRetryPolicy")
private YourRetryPolicy yourRetryPolicy;

//...

RetryTemplate retryTemplate = new RetryTemplate();
retryTemplate.setRetryPolicy( yourRetryPolicy );

Answer 2

接受的答案僅處理特定於異常的 RetryPolicy 實例。 Spring 沒有為特定於異常的 BackOffPolicy 實例提供任何開箱即用的功能。 幸運的是，它很容易實現。

import org.springframework.classify.Classifier
import org.springframework.classify.ClassifierSupport
import org.springframework.classify.SubclassClassifier
import org.springframework.retry.RetryContext
import org.springframework.retry.backoff.BackOffContext
import org.springframework.retry.backoff.BackOffInterruptedException
import org.springframework.retry.backoff.BackOffPolicy
import org.springframework.retry.backoff.NoBackOffPolicy

class ExceptionClassifierBackoffPolicy implements BackOffPolicy {

    private static class ExceptionClassifierBackoffContext implements BackOffContext, BackOffPolicy {
        Classifier<Throwable, BackOffPolicy> exceptionClassifier
        RetryContext retryContext
        Map<BackOffPolicy, BackOffContext> policyContextMap = [:]

        ExceptionClassifierBackoffContext(Classifier<Throwable, BackOffPolicy> exceptionClassifier, RetryContext retryContext) {
            this.exceptionClassifier = exceptionClassifier
            this.retryContext = retryContext
        }

        @Override
        BackOffContext start(RetryContext context) {
            return null
        }

        @Override
        void backOff(BackOffContext backOffContext) throws BackOffInterruptedException {
            def policy = exceptionClassifier.classify(retryContext.lastThrowable)
            def policyContext = policyContextMap.get(policy)
            if (!policyContext) {
                policyContext = policy.start(retryContext)
                policyContextMap.put(policy, policyContext)
            }
            policy.backOff(policyContext)
        }
    }
    private Classifier<Throwable, BackOffPolicy> exceptionClassifier = new ClassifierSupport<Throwable, BackOffPolicy>(new NoBackOffPolicy());

    void setPolicyMap(Map<Class<? extends Throwable>, BackOffPolicy> policyMap) {
        exceptionClassifier = new SubclassClassifier<Throwable, BackOffPolicy>(policyMap, new NoBackOffPolicy());
    }

    @Override
    BackOffContext start(RetryContext context) {
        return new ExceptionClassifierBackoffContext(exceptionClassifier, context)
    }

    @Override
    void backOff(BackOffContext backOffContext) throws BackOffInterruptedException {
        def classifierBackOffContext = (ExceptionClassifierBackoffContext) backOffContext
        classifierBackOffContext.backOff(backOffContext)
    }
}

那么只需：

BackOffPolicy backOffPolicy = new ExceptionClassifierBackoffPolicy()
def policyMap = [
        (RuntimeException): new FixedBackOffPolicy(backOffPeriod: 1000),
        (IOException)     : new ExponentialRandomBackOffPolicy(initialInterval: 500, maxInterval: 360000, multiplier: 2)
] as Map<Class<? extends Throwable>, BackOffPolicy>
backOffPolicy.policyMap = backoffPolicyMap

Answer 3

聚會有點晚了，但是當您需要的是根據異常類型有不同的退避期時，擴展FixedBackoffPolicy應該可以解決問題並且非常簡單。 沿着這些路線的東西：

首先，您創建退避策略類，該類接收每個異常類型具有不同退避周期的映射：

public class MultipleExceptionsBackoffPolicy extends FixedBackoffPolicy 
{
    private Classifier<Throwable, Long> classifier;

    public MultipleExceptionsBackoffPolicy (final Map<Class<? extends Throwable>, Long> throwableBackoffMap) {
        classifier = new SubclassClassifier<>(throwableBackoffMap, 5_000L) // default is 5s
    }

    @Override
    protected void doBackOff() exception BackOffInterruptedException {
        final backoff = classifier.classify(RetrySynchronizationManager.getContext().getLastThrowable());
        setBackOffPeriod(backoff);
        super.doBackOff();
    }
}

那么你必須創建一個自定義攔截器，例如：

@Bean
public Object myCustomInterceptor (){
    var exBackoffMap = Map.of(
        ExceptionTypeOne.class, 2_000L, // If ExceptionTypeOne happens, backoff period is 2s
        ExceptionTypeTwo.class, 7_000L // and if ExceptionTypeTwo happens, the backoff period is 7s
    )
    return RetryInterceptorBuilder
                .stateless()
                .retryPolicy(new SimpleRetryPolicy(3)) // always 3 attempts no matter what
                .backOffPolicy(new MultipleExceptionsBackoffPolicy(exBackoffMap))
                .build();
}

最后，您只需在可重試中配置自定義攔截器：

@Retryable(interceptor="myCustomInterceptor")
public @interface MyRetryable {}