调用函数直到发生异常的 Guava 重试器

Question

假设我有这样的代码：

public void deleteResource(UUID resourceId) {
    deleteFromDb();
    deleteFromALotOfOtherPlaces();    // Takes a long time!
}

public DescribeResourceResult describeResource(UUID resourceId) throws ResourceNotFoundException {
    return getResourceDescription(resourceId);
}

遗憾的是，删除并不表示已完成。验证删除是否已完成的唯一方法是调用 describeResource，如果资源已被删除，它将抛出异常。

我想编写一个重复调用 describeResrouce 直到 ResourceNotFoundException 发生的重试器。我该怎么做？

这是我目前的情况：

final Retryer<ResourceNotFoundException> deleteResourceRetryer = RetryerBuilder.<ResourceNotFoundException>newBuilder()
                .withWaitStrategy(WaitStrategies.fixedWait(500, TimeUnit.MILLISECONDS))
                .withStopStrategy(StopStrategies.stopAfterDelay(10, TimeUnit.SECONDS))
                .build();

// Error: Bad return type in lambda expression: DescribeResourceResult cannot be converted to ResourceNotFoundException
deleteResourceRetryer.call(() -> describeResource(resourceId));

谢谢！

Answer 1

我对 Guava 的 Retryer 不太熟悉，因此经过短暂的调查后我找不到现成的 StopStrategy，所以我的建议是自己实现它

static class OnResourceNotFoundExceptionStopStrategy implements StopStrategy {

    @Override
    public boolean shouldStop(Attempt attempt) {
        if (attempt.hasException() 
                     && attempt.getExceptionCause() instanceof ResourceNotFoundException) {
            return true;
        }
        return false;
    }

}

使用该策略，当您抓到 ResourceNotFoundException 时，重试将停止。之后修复类型并正确定义 Retryer

final Retryer<DescribeResourceResult> deleteResourceRetryer = RetryerBuilder
            .<DescribeResourceResult>newBuilder()
            .retryIfResult(Predicates.notNull())
            .withWaitStrategy(WaitStrategies.fixedWait(500, TimeUnit.MILLISECONDS))
            .withStopStrategy(new OnResourceNotFoundExceptionStopStrategy())
            .build();

最后，开始重试

try {
    deleteResourceRetryer.call(() -> describeResource(resourceId));
} catch (ExecutionException e) {
    // should not happens, because you will retry if any exception rather
    // than ResourceNotFoundException raised in your describeResource method
} catch (RetryException e) {
    // should not happens, because my implementation of StopStrategy
    // (as it looks in this example) is effectively infinite, until target exception.
    // For sure you're free to override it to anything you want
}

希望对您有所帮助！

Answer 2

使用Failsafe:

RetryPolicy<Object> retryPolicy = new RetryPolicy<>()
  .abortOn(ResourceNotFoundException.class);
  .withDelay(Duration.ofMillis(500))
  .withMaxDuration(Duration.ofSeconds(10)); 

Failsafe.with(retryPolicy).get(() -> getResourceDescription(resourceId));

调用函数直到发生异常的 Guava 重试器

Guava retryer that calls a function until an exception occurs

java

guava