如果Alicloud CMS报警未显示数据，可能是由于以下原因导致的：

1. 数据未上报：首先需要确保数据已经正确上报到Alicloud CMS。可以通过以下代码示例来确认数据是否上报成功：

import com.aliyun.openservices.aliyun.log.producer.LogProducer;
import com.aliyun.openservices.aliyun.log.producer.LogProducerBuilder;
import com.aliyun.openservices.aliyun.log.producer.ProjectConfig;
import com.aliyun.openservices.log.common.LogItem;
import com.aliyun.openservices.log.common.LogStore;

public class CmsDataUploadExample {
    public static void main(String[] args) {
        String endpoint = "";
        String project = "";
        String logstore = "";
        String accessKeyId = "";
        String accessKeySecret = "";

        ProjectConfig projectConfig = new ProjectConfig(endpoint, project, accessKeyId, accessKeySecret);

        LogProducer producer = LogProducerBuilder.builder()
                .projectConfig(projectConfig)
                .build();

        try {
            producer.putLogs(new LogStore(project, logstore), new LogItem());
            producer.flush();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            producer.close();
        }
    }
}

2. 报警规则配置错误：确认报警规则是否正确配置。可以通过以下代码示例来创建报警规则：

import com.aliyun.openservices.cms.builder.AlarmBuilder;
import com.aliyun.openservices.cms.builder.ConditionBuilder;
import com.aliyun.openservices.cms.builder.ExpressionBuilder;
import com.aliyun.openservices.cms.builder.MetricBuilder;
import com.aliyun.openservices.cms.client.CmsClient;
import com.aliyun.openservices.cms.model.request.CreateAlarmRequest;

public class CmsAlarmConfigurationExample {
    public static void main(String[] args) {
        String endpoint = "";
        String accessKeyId = "";
        String accessKeySecret = "";

        CmsClient client = new CmsClient(endpoint, accessKeyId, accessKeySecret);

        CreateAlarmRequest request = new CreateAlarmRequest();
        request.setGroupId("");
        request.setNamespace("");
        request.setMetricName("");

        MetricBuilder metricBuilder = MetricBuilder.create();
        metricBuilder.field("").gt(0);

        ConditionBuilder conditionBuilder = ConditionBuilder.create();
        conditionBuilder.and(metricBuilder);

        ExpressionBuilder expressionBuilder = ExpressionBuilder.create();
        expressionBuilder.condition(conditionBuilder);

        AlarmBuilder alarmBuilder = AlarmBuilder.create();
        alarmBuilder.name("")
                .expression(expressionBuilder)
                .level("")
                .period(Integer.parseInt(""))
                .statistics("")
                .threshold(0);

        request.setAlarm(alarmBuilder);
        
        try {
            client.createAlarm(request);
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            client.shutdown();
        }
    }
}

以上代码示例分别演示了数据上传和报警规则配置的过程。如果数据已经成功上报，且报警规则已经正确配置，但仍然无法显示报警数据，可能需要进一步检查报警规则的配置条件和数据上报的情况。同时，也可以查看Alicloud CMS的文档和API参考，以获取更详细的帮助和指导。