java - 在 App Engine Java Servlet 中查询数据存储区统计信息时出现 NullpointerException

Question

在我的应用程序的 Servlet 中，我想控制其数据存储区是否为空(我第一次运行 servlet 时它将为空，但现在情况并非如此，因为我已经填充了它并使其持久化)在继续其余代码之前。在此Datastore Docs我发现了一种查询数据存储并获取不同类型统计信息的方法。但是在执行时:

DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();
Entity globalStat = datastore.prepare(new Query("__Stat_Total__")).asSingleEntity();
Long totalBytes = (Long) globalStat.getProperty("bytes");
Long totalEntities = (Long) globalStat.getProperty("count");

我得到一个NullPointerException当我尝试存储两个 Long 变量时。为什么是Entity globalStat查询后对象为空？

编辑 1:附加信息

我正在尝试在使用 List<Entity> 填充数据存储区统计信息后获取数据存储区统计信息。实体数量:

public class MyServlet extends HttpServlet {
    ArrayList<Tour> m_tours = new ArrayList<Tour>();
    Key tourKey;
    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();

    //.... some code
    private DatastoreService populateDatastore(){
        //... some other code ...
        List<Entity> List = Arrays.asList(tour,tour1,tour2,tour3,
                                     tour4,tour5,tour6,tour7,tour8);
        datastore.put(List);
        Entity globalStat = datastore.prepare(
                             new Query("__Stat_Total__")).asSingleEntity();

        try{
            Long totalEntities = (Long) globalStat.getProperty("count");
            Long totalBytes = (Long) globalStat.getProperty("bytes");
        }catch (NullPointerException e){
            e.printStackTrace();
        }` 
    }
}

这表明实体全局统计对象在调试工具中仍然显示为空:

怎么会new Query("__Stat_Total__")).asSingleEntity();当我刚刚用多个实体填充数据存储区时不会产生任何结果？

Answer 1

ANSWER: as reported here: Using App Engine Datastore Low Level API with Java, "Stat_Total" and "Stat_Kind" don't work in a local development server. They only work when deployed in App Engine Server.