GWT-Objectify : basic

I've been through a few documentations, but am not able to communicate to the datastore yet...can anyone give me a sample project/code of objectify used in GWT web app(I use eclipse)...just a s开发者_如何学编程imple 'put' and 'get' action using RPC should do...or, atleast tell me how its done

Easiest way to understand how to make objectify work is to repeat all steps described in this article from David's Chandler blog. Whole blog is a pretty much must read if you interested in GWT, GAE(Java), gwt-presenter, gin\guice,etc. There you will find working example, but anyway here i'll show a slighly advanced example.

In package shared define your entity/model:

import javax.persistence.Embedded;
import javax.persistence.Id;
import com.google.gwt.user.client.rpc.IsSerializable;
import com.googlecode.objectify.Key;
import com.googlecode.objectify.annotation.Entity;
import com.googlecode.objectify.annotation.Unindexed;

@Entity
public class MyEntry implements IsSerializable {
    // Objectify auto-generates Long IDs just like JDO / JPA
    @Id private Long id;
    @Unindexed private String text = "";
    @Embedded private Time start;

    // empty constructor for serialization
    public MyEntry () {
    }
    public MyEntry (Time start, String text) {
        super();
        this.text = tText;
        this.start = start;
    }
    /*constructors,getters,setters...*/
}

Time class (also shared package) contains just one field msecs:

@Entity  
public class Time implements IsSerializable, Comparable<Time> {
protected int msecs = -1;    
  //rest of code like in MyEntry 
}

Copy class ObjectifyDao from link above to your server.dao package. And then make DAO class specifically for MyEntry -- MyEntryDAO:

package com.myapp.server.dao;

import java.util.logging.Logger;

import com.googlecode.objectify.ObjectifyService;
import com.myapp.shared.MyEntryDao;

public class MyEntryDao extends ObjectifyDao<MyEntry>
{
    private static final Logger LOG = Logger.getLogger(MyEntryDao.class.getName());

    static
    {
        ObjectifyService.register(MyEntry.class);
    }

    public MyEntryDao()
    {
        super(MyEntry.class);
    }

}

Finally we can make requests to database(server package):

public class FinallyDownloadingEntriesServlet extends HttpServlet {
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws
ServletException, IOException {
        resp.setCharacterEncoding("UTF-8");
        resp.setContentType("text/plain");
                //more code...
                resp.setHeader("Content-Disposition", "attachment; filename=\""+"MyFileName"+".txt\";");
        try {
            MyEntryDao = new MyEntryDao();
          /*query to get all MyEntries from datastore sorted by start Time*/
            ArrayList<MyEntry> entries = (ArrayList<MyEntry>) dao.ofy().query(MyEntry.class).order("start.msecs").list();

            PrintWriter out = resp.getWriter();
            int i = 0;
            for (MyEntry entry : entries) {
                ++i;
                out.println(i);
                out.println(entry.getStart() + entry.getText());
                out.println();
            }
        } finally {
            //catching exceptions
        }
    }