Maksim Maksim - 2 months ago 12
Java Question

GWT with JDO problem

I just start playing with GWT I'm having a really hard time to make GWT + JAVA + JDO + Google AppEngine working with DataStore.
I was trying to follow different tutorial but had no luck. For example I wend to these tutorials: TUT1 TUT2

I was not able to figure out how and what i need to do in order to make this work.
Please look at my simple code and tell me what do i need to do so i can persist it to the datastore:

1. ADDRESS ENTITY

package com.example.rpccalls.client;

import java.io.Serializable;

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

public class Address implements Serializable{

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private int addressID;
@Persistent private String address1;
@Persistent private String address2;
@Persistent private String city;
@Persistent private String state;
@Persistent private String zip;

public Address(){}

public Address(String a1, String a2, String city, String state, String zip){
this.address1 = a1;
this.address2 = a2;
this.city = city;
this.state = state;
this.zip = zip;
}

/* Setters and Getters */
}


2. PERSON ENTITY

package com.example.rpccalls.client;

import java.io.Serializable;
import java.util.ArrayList;

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

import com.google.appengine.api.datastore.Key;

@PersistenceCapable
public class Person implements Serializable{

@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
private Key key;
@Persistent private String name;
@Persistent private int age;
@Persistent private char gender;
@Persistent ArrayList<Address> addresses;

public Person(){}

public Person(String name, int age, char gender){
this.name = name;
this.age = age;
this.gender = gender;
}

/* Getters and Setters */
}


3. RPCCalls

package com.example.rpccalls.client;

import java.util.ArrayList;

import com.google.gwt.core.client.EntryPoint;
import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.RootPanel;
import com.google.gwt.user.client.ui.TextBox;


public class RPCCalls implements EntryPoint {

private static final String SERVER_ERROR = "An error occurred while attempting to contact the server. Please check your network connection and try again.";

private final RPCCallsServiceAsync rpccallService = GWT.create(RPCCallsService.class);

TextBox nameTxt = new TextBox();
Button btnSave = getBtnSave();

public void onModuleLoad() {

RootPanel.get("inputName").add(nameTxt);
RootPanel.get("btnSave").add(btnSave);
}



private Button getBtnSave(){

Button btnSave = new Button("SAVE");

btnSave.addClickHandler(
new ClickHandler(){
public void onClick(ClickEvent event){
saveData2DB(nameTxt.getText());
}
}
);
return btnSave;
}

void saveData2DB(String name){
AsyncCallback<String> callback = new AsyncCallback<String>() {
public void onFailure(Throwable caught) {
Window.alert("WOOOHOOO, ERROR: " + SERVER_ERROR);
// TODO: Do something with errors.
}

public void onSuccess(String result) {
Window.alert("Server is saying: ' " + result + "'");
}

};

ArrayList<Address> aa = new ArrayList<Address>();
aa.add(new Address("123 sasdf","", "Some City", "AZ", "93923-2321"));
aa.add(new Address("23432 asdf", "Appt 34", "Another City", "AZ", "43434-4432"));

Person p = new Person();
p.setName(name);
p.setAge(23);
p.setGender('m');
p.setAddresses(aa);

// !!!!!!!!!!!!!!!!!! SERVER CALL !!!!!!!!!!!!!!!!!!
rpccallService.saveName(p, callback);
// !!!!!!!!!!!!!!!!!! SERVER CALL !!!!!!!!!!!!!!!!!!

}
}


4. RPCCallsService

package com.example.rpccalls.client;

import com.google.gwt.user.client.rpc.RemoteService;
import com.google.gwt.user.client.rpc.RemoteServiceRelativePath;

@RemoteServiceRelativePath("calls")
public interface RPCCallsService extends RemoteService {

String saveName(Person p);

}


5. RPCCallsServiceAsync

package com.example.rpccalls.client;

import com.google.gwt.user.client.rpc.AsyncCallback;

public interface RPCCallsServiceAsync {

void saveName(Person p, AsyncCallback<String> callback);

}


6. **RPCCalls.gwt.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 1.6.4//EN" "http://google-web-toolkit.googlecode.com/svn/tags/1.6.4/distro-source/core/src/gwt-module.dtd">
<module rename-to='rpccalls'>
<inherits name='com.google.gwt.user.User'/>
<inherits name='com.google.gwt.user.theme.standard.Standard'/>
<entry-point class='com.example.rpccalls.client.RPCCalls'/>
</module>


I tried to add Key class and everything else in those tutorials but it looks like i'm missing something.

Here is my error:
alt text

or before i was getting this error:


Key cannot be resolved to a type


What is the best solution to make this working?

Answer

Sriram Narayan says to String-encode the Key to get it to pass through GWT's RPC mechanism:

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class SomeDomainClass implements Serializable {
@PrimaryKey
@Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
@Extension(vendorName = "datanucleus", key = "gae.encoded-pk", value = "true")
String id;

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