GWT Simple RPC use case problem : Code included

Question

I am trying to work out how to send a domain object from the server-side to the client-side using GWT RPC. I've coded a really simple use case that represents the sort of thing I (and others?) need to be able to do but presently can't get to work.

I have scoured the docs, tutorials and forums but they either show Strings being passed around or offer explanations that (when I apply them to this) still don't work.

Hopefully someone can explain to me and others why this code doesn't work and how to get it to work.

Thank you.

Here are the error messages.

13:12:54.328 [DEBUG] [org.redboffin.worldhug.Test] Validating newly compiled units
13:12:54.328 [ERROR] [org.redboffin.worldhug.Test] Errors in 'file:/C:/Documents%20and%20Settings/Darren/workspace/WorldHug/src/org/redboffin/worldhug/client/test/TestService.java'
13:12:54.343 [ERROR] [org.redboffin.worldhug.Test] Line 14: No source code is available for type org.redboffin.worldhug.server.test.TestObject; did you forget to inherit a required module?
13:12:54.515 [ERROR] [org.redboffin.worldhug.Test] Errors in 'file:/C:/Documents%20and%20Settings/Darren/workspace/WorldHug/src/org/redboffin/worldhug/client/test/TestServiceAsync.java'
13:12:54.515 [ERROR] [org.redboffin.worldhug.Test] Line 12: No source code is available for type org.redboffin.worldhug.server.test.TestObject; did you forget to inherit a required module?
13:12:55.953 [ERROR] [org.redboffin.worldhug.Test] Errors in 'file:/C:/Documents%20and%20Settings/Darren/workspace/WorldHug/src/org/redboffin/worldhug/client/test/TestView.java'
13:12:55.968 [ERROR] [org.redboffin.worldhug.Test] Line 42: No source code is available for type org.redboffin.worldhug.server.test.TestObject; did you forget to inherit a required module?
13:12:55.968 [ERROR] [org.redboffin.worldhug.Test] Line 46: No source code is available for type org.redboffin.worldhug.server.test.InnerObject; did you forget to inherit a required module?
13:12:55.984 [ERROR] [org.redboffin.worldhug.Test] Line 48: No source code is available for type org.redboffin.worldhug.server.test.ListObject; did you forget to inherit a required module?
13:12:56.765 [INFO] [org.redboffin.worldhug.Test] Module org.redboffin.worldhug.Test has been loaded

Here are the project classes and files.

Test.gwt.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE module PUBLIC "-//Google Inc.//DTD Google Web Toolkit 2.0.0//EN" "http://google-web-toolkit.googlecode.com/svn/tags/2.0.0/distro-source/core/src/gwt-module.dtd">
<module>
    <inherits name="com.google.gwt.user.User" />
    <source path="client/test" />
    <entry-point class="org.redboffin.worldhug.client.test.Test"></entry-point>
</module>

Web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>

  <!-- Servlets -->

  <servlet>
    <servlet-name>testServlet</servlet-name>
    <servlet-class>org.redboffin.worldhug.server.test.TestServiceImpl</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>testServlet</servlet-name>
    <url-pattern>/worldhug/test/testService</url-pattern>
  </servlet-mapping>

  <!-- Default page to serve -->
  <welcome-file-list>
    <welcome-file>test.html</welcome-file>
  </welcome-file-list>

</web-app>

TestObject.java

package org.redboffin.worldhug.server.test;

import java.util.ArrayList;
import java.util.List;

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

public class TestObject implements IsSerializable {

    private String testObjectString;
    private InnerObject innerObject;
    private List<ListObject> listObjects = new ArrayList<ListObject>();

    public TestObject() {}

    // Getters and setters removed for brevity

}

InnerObject.java

package org.redboffin.worldhug.server.test;

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

public class InnerObject implements IsSerializable {

    private String innerObjectString;

    public InnerObject() {}

        // Getters and setters removed for brevity

}

ListObject.java

package org.redboffin.worldhug.server.test;

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

public class ListObject implements IsSerializable {

    private String listObjectString;

    public ListObject() {}

        // Getters and setters removed for brevity.

}

TestService.java

package org.redboffin.worldhug.client.test;

import org.redboffin.worldhug.server.test.TestObject;

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

/**
 * The client side stub for the Test Service.
 * @author Darren
 */
@RemoteServiceRelativePath("testService")
public interface TestService extends RemoteService {

    TestObject test();

}

TestServiceAsync.java

package org.redboffin.worldhug.client.test;

import org.redboffin.worldhug.server.test.TestObject;

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

/**
 * The async counterpart of <code>TestService</code>.
 * @author Darren
 */
public interface TestServiceAsync {

    void test(AsyncCallback<TestObject> callback);

}

TestServiceImpl.java

package org.redboffin.worldhug.server.test;

import java.util.List;

import org.redboffin.worldhug.client.test.TestService;

import com.google.gwt.user.server.rpc.RemoteServiceServlet;

/**
 * The server side implementation of the RPC service.
 * @author Darren
 */
@SuppressWarnings("serial")
public class TestServiceImpl extends RemoteServiceServlet implements TestService {

    @Override
    public TestObject test() {

        TestObject testObject = new TestObject();       
        testObject.setTestObjectString("Test Object String");

        InnerObject innerObject = new InnerObject();
        innerObject.setInnerObjectString("Inner Object String");

                testObject.setInnerObject(innerObject);

        List<ListObject> listObjects = testObject.getListObjects();

        ListObject listObjectOne = new ListObject();
        listObjectOne.setListObjectString("List Object One");
        listObjects.add(0, listObjectOne);

        ListObject listObjectTwo = new ListObject();
        listObjectTwo.setListObjectString("List Object Two");
        listObjects.add(0, listObjectTwo);

        ListObject listObjectThree = new ListObject();
        listObjectThree.setListObjectString("List Object Three");
        listObjects.add(0, listObjectThree);

        return testObject;
    }

}

TestView.java

package org.redboffin.worldhug.client.test;

import java.util.ArrayList;
import java.util.Iterator;

import org.redboffin.worldhug.server.test.InnerObject;
import org.redboffin.worldhug.server.test.ListObject;
import org.redboffin.worldhug.server.test.TestObject;

import com.google.gwt.core.client.GWT;
import com.google.gwt.event.dom.client.ClickEvent;
import com.google.gwt.uibinder.client.UiBinder;
import com.google.gwt.uibinder.client.UiField;
import com.google.gwt.uibinder.client.UiHandler;
import com.google.gwt.user.client.rpc.AsyncCallback;
import com.google.gwt.user.client.ui.Button;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.VerticalPanel;

public class TestView extends Composite {

    private static TestViewUiBinder uiBinder = GWT.create(TestViewUiBinder.class);

    interface TestViewUiBinder extends UiBinder<VerticalPanel, TestView> {}

    @UiField Label testObjectStringLabel;
    @UiField Label innerObjectStringLabel;
    @UiField VerticalPanel listObjectsPanel;
    @UiField Button button;
    @UiField Label errorMessageLabel;

    public TestView(String firstName) {
        initWidget(uiBinder.createAndBindUi(this));
    }

    @UiHandler("button")
    void onClick(ClickEvent e) {

        TestServiceAsync testService = (TestServiceAsync) GWT.create(TestService.class);

        AsyncCallback<TestObject> callback = new AsyncCallback<TestObject>() {

            public void onSuccess(TestObject testObject) {
                testObjectStringLabel.setText(testObject.getTestObjectString());
                InnerObject innerObject = testObject.getInnerObject();
                innerObjectStringLabel.setText(innerObject.getInnerObjectString());
                ArrayList<ListObject> listObjects = (ArrayList<ListObject>) testObject.getListObjects();
                Iterator<ListObject> iterator = listObjects.iterator();
                while(iterator.hasNext()) {
                    ListObject listObject = (ListObject) iterator.next();
                    listObjectsPanel.add(new Label(listObject.getListObjectString()));
                }
            }

            public void onFailure(Throwable caught) {
                errorMessageLabel.setText("Error : "+caught.getMessage());
            }
          };

          testService.test(callback);

    }

}

TestView.ui.xml

<!DOCTYPE ui:UiBinder SYSTEM "http://dl.google.com/gwt/DTD/xhtml.ent">
<ui:UiBinder 
    xmlns:ui="urn:ui:com.google.gwt.uibinder"
    xmlns:g="urn:import:com.google.gwt.user.client.ui">

    <g:VerticalPanel>
        <g:Label>Test Object</g:Label>
        <g:Label ui:field="testObjectStringLabel"></g:Label>
        <g:VerticalPanel>
            <g:Label>Inner Object</g:Label>
            <g:Label ui:field="innerObjectStringLabel"></g:Label>
        </g:VerticalPanel>
        <g:VerticalPanel ui:field="listObjectsPanel">
            <g:Label>List Objects</g:Label>
        </g:VerticalPanel>
        <g:Button ui:field="button">Display Test Object</g:Button>
        <g:Label ui:field="errorMessageLabel"></g:Label>
    </g:VerticalPanel>

</ui:UiBinder>

Thank you for reading this far and for any help you may be able to give me (and others).

Featherhead

The amount of boilerplate code in Java RPC bothers me more than anything else in Java. I really wish, in this case at least, they'd take the Convention Over Configuration approach of Ruby and just let you drop a serializable object on the line. I've actually tried this approach, having an arrivedAt() method called whenever you arrived at a new VM. It was really slick but the arrivedAt method had a tendency to pull the entire client AND server into each build. Gave up but I have this idea of being able to tag methods @client or @server and conditionally compile them... – Churn

Answer 1

You need to identify all packages that contain source that is to be GWT compiled.

e.g.

<source path="client/test"/>
<source path="server/test"/>

It might be a better option to put your domain classes NOT in the server package. We often do this kind of thing:

<source path="client"/>
<source path="shared"/>

where shared contains the DTOs passed back and forth between client and server.

Baldric

Thank you Craig - that now works perfectly. Great tip on using a 'shared' package. – Featherhead

Answer 2

If use the DTO you must insert tranferable object in shared folder (convention). If use domain object non shared and not "transfer" you can insert folder (e.g "domain") in server folder, but this "type" can't be used for asynchronous calls. Moral: if an object is transferred must be "shared", otherwise you can safely use in the server folder.

Eocene

I agree about to share. But the insert the class files inside the server folder is a wrong way. – Flexile