指定维度时如何获取指标统计信息？

Question

我正在尝试使用aws java sdk来收集有关单个ec2实例的度量标准统计信息。我可以成功获取聚合数据，但是当我尝试指定任何维度（例如实例类型或ID）时，我开始得到一个空结果集。下面是我的测试代码，该代码返回一个空的数据集，但是如果我删除了.withDimensions（）调用，则可以使用。关于我在做什么错的任何建议吗？

    final BasicAWSCredentials basicAWSCredentials = new BasicAWSCredentials("accesskey", "secretkey");
    final AWSStaticCredentialsProvider credentialsProvider = new AWSStaticCredentialsProvider(basicAWSCredentials);

    final AmazonCloudWatch cw =
            AmazonCloudWatchClientBuilder.standard()
                    .withRegion(Regions.US_EAST_1)
                    .withCredentials(credentialsProvider)
                    .build();

    final int oneHour = 60 * 60;

    final long oneDay = oneHour * 24 * 1000;

    GetMetricStatisticsRequest request = new GetMetricStatisticsRequest()
            .withStartTime(new Date(new Date().getTime() - oneDay))
            .withNamespace("AWS/EC2")
            .withPeriod(60 * 5)
            .withDimensions(new Dimension().withName("InstanceType").withValue("m4.large"))
            .withMetricName("CPUUtilization")
            .withStatistics("Maximum", "Average", "Sum", "Minimum", "SampleCount")
            .withEndTime(new Date());

    GetMetricStatisticsResult result = cw.getMetricStatistics(request);

    System.out.print(result);