Google App Engine（Java）数据存储统计API导致错误

Question

I'm trying to implement Google App Engine's default Datastore Statistics API example:

http://code.google.com/appengine/docs/java/datastore/stats.html

import com.google.appengine.api.datastore.DatastoreService;
import com.google.appengine.api.datastore.DatastoreServiceFactory;
import com.google.appengine.api.datastore.Entity;
import com.google.appengine.api.datastore.Query;

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

I get a java.lang.NullPointerException when trying to access the globalStat object properties. I'm testing locally, does this API only work in production or am I missing something?

Thanks

Answer 1

If you look at the javadoc for the DatastoreService class, it doesn't look like there's a prepare method. I believe you are supposed to just use the get and put methods, where the get methods parameters would be the "key" for what you're trying to get, and the put method's parameter would just be the entity you created's object.