appengine 1.5.5 prerelease , XG(Cross Group) tx sample.

XGtxTestingServlet.java

package net.vvakame.xg;

import java.io.IOException;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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.EntityNotFoundException;
import com.google.appengine.api.datastore.Key;
import com.google.appengine.api.datastore.KeyFactory;
import com.google.appengine.api.datastore.Transaction;
import com.google.appengine.api.datastore.TransactionOptions;

@SuppressWarnings("serial")
public class XGtxTestingServlet extends HttpServlet {

	DatastoreService db;

	public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws IOException {
		resp.setContentType("text/plain");

		// over 6 => too many entity groups...
		int count = 5;
		{
			String countStr = req.getParameter("count");
			if (countStr != null) {
				count = Integer.parseInt(countStr);
			}
		}
		int egCount = 1000;
		{
			String countStr = req.getParameter("egCount");
			if (countStr != null) {
				egCount = Integer.parseInt(countStr);
			}
		}
		resp.getWriter().println("count=" + count + ", egCount=" + egCount);

		db = DatastoreServiceFactory.getDatastoreService();

		String kind = "hoge";

		for (int i = 1; i <= count; i++) {
			createEntityGroups(kind + i, i, egCount);
		}

		TransactionOptions opt = TransactionOptions.Builder.withXG(true);
		Transaction tx = db.beginTransaction(opt);

		for (int i = 1; i <= count; i++) {
			Entity entity = get(tx, KeyFactory.createKey(kind + i, i));
			incProperty(entity, "i");
			db.put(tx, entity);
		}

		tx.commit();
	}

	void createEntityGroups(String kind, long id, int count) {

		Key parentKey = KeyFactory.createKey(kind, id);
		{
			Entity entity = new Entity(parentKey);
			entity.setProperty("keyStr", parentKey.toString());
			db.put(entity);
		}

		for (int i = 1; i <= count; i++) {
			Key key = KeyFactory.createKey(parentKey, kind, i);
			Entity entity = new Entity(key);
			entity.setProperty("keyStr", key.toString());
			db.put(entity);
		}
	}

	Entity get(Transaction tx, Key key) {
		try {
			return db.get(tx, key);
		} catch (EntityNotFoundException e) {
			throw new RuntimeException(e);
		}
	}

	void incProperty(Entity entity, String propertyName) {
		Long value = (Long) entity.getProperty(propertyName);
		if (value == null) {
			value = 1L;
		} else {
			value++;
		}
		entity.setProperty(propertyName, value);
	}
}