Flex / Grails CRUD application with GraniteDS, reloaded

Now with Flex 4, Spring Security 3, data push...


It's been almost one year since the last blog entry about the gdsflex plugin. We have just released the version 0.8 of the plugin that brings compatibility with all new releases of the various technologies involved: Grails 1.2/1.3, Flex 4, Spring Security 3... It's time to update the tutorial for this whole new stack.

For the purpose of this article, I'll just write the same boring book application that I've demonstrated before, and simply add additional capabilities: security and data push.

The first important thing before starting is that you now need to install a Flex SDK somewhere and set the FLEX_HOME environment variable to point to its path. It you want to use a Flex 4, that will look like FLEX_HOME = /home/will/flex_sdk_4.
Older versions of the plugin used to embark a full Flex SDK for ease of use, but using FLEX_HOME allows for easier upgrades of the Flex SDK and is more in line with the behaviour of other Grails plugins.

You will also need Grails 1.3.1+ installed and set up (the plugin also works with Grails 1.2.2+ but that could need some minor adjustments in the following steps). Now type from the command line :

grails create-app bookmanager

cd bookmanager

grails install-plugin gdsflex

Part 1 : Define the domain classes and generate a scaffolded Flex application

Just as before, the core of the application is centered on Grails, and more precisely on the domain classes, following usual Grails domain-driven style. Once again we'll start by an Author class.

grails create-domain-class Author

grails-app/domain/bookmanager/Author.groovy

package bookmanager

class Author {
   
    static constraints = {
        name(size:0..50, blank:false)
        birthDate(format:'DD/MM/YYYY')
        picture(nullable:true, widget:'image')
    }
   
    String uid
   
    String name
   
    Date birthDate
   
    java.sql.Blob picture
}

And the corresponding controller, here using scaffolding for simplicity :

grails create-controller Author

grails-app/controllers/bookmanager/AuthorController.groovy

package bookmanager

@org.granite.tide.annotations.TideEnabled
class AuthorController {

    def index = { redirect(action:list, params:params) }
    
    def scaffold = Author
}

This is not much different from the previous blog examples. Just notice how Grails 1.3 automatically puts domain classes and controllers in a package with the same name than the application.
As always the TideEnabled annotation exposes the controller to the Flex client.

Now we can generate and compile the Flex application :

grails generate-flex-app

grails mxmlc

grails run-app

And go to http://localhost:8080/bookmanager/bookmanager.swf.

You can see a basic working Flex application that allows to create and edit authors. For now the generated app still uses Flex 3 Halo components and not Flex 4 Spark components, but it can perfectly be compiled and run with the Flex 4 SDK.
Future releases of the plugin will generate a Flex 4 Spark application.



What has happened ?
The generate-flex-app script has generated a basic mxml that handles CRUD operations using the Tide UI builder library in grails-app/view/flex/bookmanager.mxml.
The mxmlc script triggers the Flex compiler to build the application swf in grails-app/views/swf.

The Grails server is now started from this terminal, open a new terminal/command line editor to type the next commands.

Now let's add a couple of other classes with associations.

grails create-domain-class Book

grails create-domain-class Chapter

grails create-controller Book

grails-app/domain/bookmanager/Book.groovy

package bookmanager

class Book {
    
    static constraints = {
        title(size:0..100, blank:false)
        category(inList:["Fiction", "Non-fiction", "Biography"])
        author()
        description(size:0..2000, widget:"textArea")
        chapters(editable:true)
    }
    
    String uid
    
    String title
   
    String category
    
    Author author
    
    Set chapters
   
    String description
    
    static hasMany = [ chapters:Chapter ]   
    static mapping = {
        author fetch:"join"
        chapters cascade:"all-delete-orphan"
    }
}

grails-app/domain/bookmanager/Chapter.groovy

package bookmanager

class Chapter {
   
    static constraints = {
        title(size:0..50, blank:false)
    }
   
    String uid
   
    Book book
   
    String title
   
    String summary
    
    static mapping = {
        book fetch:"join"
    }
}

grails-app/controllers/bookmanager/BookController.groovy

package bookmanager

@org.granite.tide.annotations.TideEnabled
class BookController {

    def index = { redirect(action:list, params:params) }
    
    def scaffold = Book
}

An important thing is that ManyToOne associations must be marked fetch:"join" or lazy:false. GraniteDS does not support transparent lazy loading for single ended associations, and most likely never will (it would generate unacceptable network and database traffic, one http request and one SQL query for each uninitialized entity). Lazy collections are supported, so OneToMany and ManyToMany associations do not have to be marked lazy:false.

Once the domain classes written, we can generate their Flex ActionScript 3 equivalents with :

grails gas3

An add a Book entry to the main menu in grails-app/view/flex/bookmanager.mxml.

...
<mx:LinkButton label="Books" width="100%" textAlign="left"
  click="mainStack.selectedChild = bookUI" />
...
<ui:EntityUI id="bookUI" 
  entityClass="{Book}" 
  width="100%" height="100%"/>
...

I won't get into much details about the EntityUI stuff. It comes from the built-in Tide UI builder library that enables the dynamic client-side scaffolding.
For real applications, you should write your own Flex UI to obtain a really rich and usable interface. The auto generated application can be mostly seen as a quick and dirty prototype.

We can now create and edit books, and see how many-to-one and one-to-many associations are displayed in the generated application.

If you eventually tried to add chapters, you will see that it does not work. There are indeed two minor changes to do manually in the AS3 classes to help the UI builder make the link between the associated oneToMany entities: initialize the Chapters collection in the Book.as class, and add a constructor in Chapter.as :

grails-app/views/flex/bookmanager/Book.as

public function Book():void {
    chapters = new ArrayCollection();
}

grails-app/views/flex/bookmanager/Chapter.as

public function Chapter(book:Book = null):void {
    this.book = book;
}

Once these changes are made, just refresh the browser and check that you can add chapters to your books. Notice how the Gas3 generator and the Flex compiler have been triggered automatically in the background in the running Grails window.

Part 2 : Securing the application

In a real application, it would required that only authenticated users can access enterprise data. Since 0.8, the gdsflex plugin supports the spring-security-core plugin that integrates with Spring Security 3.

Stop the Grails server, and install the plugin with :

grails install-plugin spring-security-core

Then generate the security domain classes Person and Authority (I don't know why, other class names have not worked with the spring-security-core 0.4.1) :

grails s2-quickstart bookmanager Person Authority

The security plugin has generated 3 domain classes : Person, Authority and PersonAuthority. As we have not configured a real database, we are simply going to add a bootstrap script to create default users and roles for our application.

grails-app/conf/Bootstrap.groovy

import bookmanager.Person
import bookmanager.Authority
import bookmanager.PersonAuthority

class BootStrap {
 
     def springSecurityService 

     def init = { servletContext ->
     
  def user_admin = new Person(username:"admin",
      password: springSecurityService.encodePassword("admin"),
      enabled:true).save()
     
  def user_user = new Person(username:"user",
      password: springSecurityService.encodePassword("user"),
      enabled:true).save()
        
  def role_admin = new Authority(description:"Admin",
      authority:"ROLE_ADMIN").save()        
  def role_user = new Authority(description:"User",
      authority:"ROLE_USER").save()
            
        new PersonAuthority(person:user_admin, authority:role_admin).save()
        new PersonAuthority(person:user_user, authority:role_user).save()
     }

     def destroy = {
     }
}

Now we need to secure access to the application and add a login page. We will make use of the built-in Tide identity component and define a ViewStack to display/hide the login page depending on the current authentication state.

Here's the relevant code to add to grails-app/views/flex/bookmanager.mxml :

<mx:Application
    ...
    
    import org.granite.tide.spring.Identity;
    import org.granite.tide.events.TideResultEvent;
    import org.granite.tide.events.TideFaultEvent;
   
    ...
    
    [Bindable] [Inject]
    public var identity:Identity;
    
    [Bindable]
    private var message:String;
 
    private function loginResult(event:TideResultEvent):void {
        message = "";
    }
 
    private function loginFault(event:TideFaultEvent):void {
        message = event.fault.faultString;
    }

    ...
    
    <mx:ViewStack id="appView" selectedIndex="{identity.loggedIn ? 1 : 0}" width="100%" height="100%">
        <mx:VBox width="100%" height="100%" verticalAlign="middle" horizontalAlign="center">
           <mx:Panel title="Login"
               horizontalAlign="center"
               verticalGap="0" paddingTop="8" paddingBottom="8"
               xmlns:mx="http://www.adobe.com/2006/mxml">

               <mx:Form>
                   <mx:FormItem label="Username">
                       <mx:TextInput id="username"/>
                   </mx:FormItem>
                   <mx:FormItem label="Password">
                       <mx:TextInput id="password" displayAsPassword="true"
                           enter="identity.login(username.text, password.text, loginResult, loginFault);"/>
                   </mx:FormItem>
               </mx:Form>
             
               <mx:Label text="{message}"/>

               <mx:Button label="Login"
                   click="identity.login(username.text, password.text, loginResult, loginFault);"/>
           </mx:Panel>
       </mx:VBox>

       <mx:VBox id="mainUI" width="100%" height="100%">
            <mx:ApplicationControlBar id="acb" width="100%">
                <mx:Label text="GraniteDS / Grails generated application" fontSize="18" fontWeight="bold" color="#f0f0f0"/>
                <mx:Spacer width="100%"/>
                <mx:Label text="Logged in as {identity.username}"/>
                <mx:Button label="Logout" click="identity.logout()"/>
            </mx:ApplicationControlBar>
            
            ...
       </mx:VBox>
       
    </mx:ViewStack>
</mx:Application>

There is nothing very sophisticated here, just notice how we make use of the identity.loggedIn property to display the correct UI and identity.login/identity.logout to trigger user login/logout.

You can restart the application, and check that you can log in with the admin/admin and user/user usernames and passwords combinations (and obviously not with others).

Note that we could also have relied on the default html login page of the spring-security-core plugin to secure the application and protect access to the swf itself. That would be the way to go to enable OpenID authentication or any other Web-based authentication model. In this case, you don't necessarily have to add a Flex login page, but you have to indicate to Flex that it has to retrieve the authentication state at startup with something like :

<mx:Application creationComplete="identity.isLoggedIn()" ... />

This can also be used to allow the authentication state to be restored after a browser page refresh.

We can now try to add more advanced authorization filtering. Let's say that we want to forbid deletion of authors by non-administrator users. This requires a few steps :

1. Enable authorization support in grails-app/conf/GraniteDSConfig.groovy

graniteConfig {
    springSecurityAuthorizationEnabled = true
    springSecurityIdentityClass = org.granite.tide.spring.security.Identity3
}

This tells GraniteDS to enable integration with Spring Security authorizations and defines the Identity3 integration class for Spring Security 3 (the one used in the spring-security-core plugin).

2. Use the Identity component

Usually you will use the Identity component with Flex data binding on component properties such as visible or enabled to hide/disable parts of the UI depending on the user access rights.
For example this will define a button that is displayed only to administrator users :

<mx:Button label="Delete" visible="{identity.ifAllGranted('ROLE_ADMIN')}" includeInLayout="{identity.ifAllGranted('ROLE_ADMIN')}"/>

In our example, it will be a bit more tricky because we use the automatic Tide UI builder. We have to override the default mxml for authors and manually set the data binding for the visible and includeInLayout properties.

grails-app/views/flex/AuthorEdit.mxml

<ui:EntityEdit 
    xmlns:mx="http://www.adobe.com/2006/mxml"
    xmlns:ui="org.granite.tide.uibuilder.*"
    xmlns="*">
    <mx:Script>
        import mx.binding.utils.BindingUtils;
        import org.granite.tide.spring.Identity;
        
        [Inject]
        public var identity:Identity;
        
        protected override function layoutForm():void {
            super.layoutForm();
            
            BindingUtils.bindProperty(this.buttonBar.getChildAt(1), "includeInLayout", identity, 
                { name: 'ifAllGranted', getter: function(identity:Identity):Boolean { return identity.ifAllGranted('ROLE_ADMIN'); } }
            );
            BindingUtils.bindProperty(this.buttonBar.getChildAt(1), "visible", identity, 
                { name: 'ifAllGranted', getter: function(identity:Identity):Boolean { return identity.ifAllGranted('ROLE_ADMIN'); } }
            );
        }
    </mx:Script>
</ui:EntityEdit>

And the override in the main mxml :

grails-app/views/flex/bookmanager.mxml

...            
Spring.getInstance().addComponentWithFactory("bookmanager.author.entityEdit", AuthorEdit, 
    { entityClass: Author }, true, true, Tide.RESTRICT_UNKNOWN, null, false);
...

Now if you restart the application, you can check that the Delete button is displayed only when you are logged in as administrator.
Note that user authorizations are retrieved from the server the first time, but are then cached locally, so it's not expensive to add as many ifAllGranted as you wish in the application.

Part 3 : Enabling data push for the application

We can now securely display, create, edit and delete our data. The last advanced feature of GraniteDS that I will show in this post is the data push that allows data updates to be propagated in near real-time to other users.
Once again it involves a few steps :

1. Configure a Tomcat NIO connector

The default Tomcat configuration included in Grails 1.2+ does not use a NIO connector. Using the NIO connector is recommended for GraniteDS data push to provide the better scalability.
It is possible to use the default connector during development but the NIO configuration is interesting (as an aside, thanks to John Fletcher for having taken the time to dig this from the deep of the Grails mailing list, see here: http://www.saltwebsites.com/blog/grails-gds-gravity-guide).
In scripts/_Events.groovy, add this :

import org.apache.catalina.connector.Connector;

eventConfigureTomcat = { tomcat ->

 def nioConnector = new Connector("org.apache.coyote.http11.Http11NioProtocol")
 nioConnector.port = 8081
 nioConnector.setProperty("redirectPort", "8443")
 nioConnector.setProperty("protocol", "HTTP/1.1")
 nioConnector.setProperty("enableLookups", "false")

 tomcat.service.addConnector nioConnector
}

Then you will have to access the application with http://localhost:8081 instead of the standard port 8080.

Note that for production use, it is highly recommended to use the native APR connector, see in the Tomcat documentation here for more information.

2. Enable Gravity/push support in grails-app/conf/GraniteDSConfig.groovy

graniteConfig {
    springSecurityAuthorizationEnabled = true 
    springSecurityIdentityClass = org.granite.tide.spring.security.Identity3 
    
    gravityEnabled = true 
    dataDispatchEnabled = true
}

3. Define a Gravity channel and destination

Then we have to define a Gravity channel and topic in the services-config.xml Flex configuration:

web-app/WEB-INF/flex/services-config.xml:

<services-config>
    <services>
        <service id="granite-service"
            class="flex.messaging.services.RemotingService"
            messageTypes="flex.messaging.messages.RemotingMessage">
   
            <destination id="spring">
                <channels>
                    <channel ref="my-graniteamf"/>
                </channels>
                <properties>
                    <factory>tideSpringFactory</factory>
                    <persistenceManagerBeanName>tidePersistenceManager</persistenceManagerBeanName>
                </properties>
            </destination>
        </service>
        
        <service id="gravity-service"
            class="flex.messaging.services.MessagingService"
            messageTypes="flex.messaging.messages.AsyncMessage">
            <adapters>
                <adapter-definition id="simple" class="org.granite.gravity.adapters.SimpleServiceAdapter"/>
            </adapters>

            <destination id="bookManagerTopic">
                <properties>
                  <session-selector>true</session-selector>
                </properties>
                <channels>
                    <channel ref="my-gravityamf"/>
                </channels>
                <adapter ref="simple"/>
            </destination>
        </service>
    </services>

    <factories>
        <factory id="tideSpringFactory" class="org.granite.tide.spring.SpringServiceFactory">
        </factory>
    </factories>

    <!--
     ! Declares my-graniteamf channel.
     !-->
    <channels>
        <channel-definition id="my-graniteamf" class="mx.messaging.channels.AMFChannel">
            <endpoint
                uri="http://{server.name}:{server.port}/{context.root}/graniteamf/amf"
                class="flex.messaging.endpoints.AMFEndpoint"/>
        </channel-definition>
        
        <channel-definition id="my-gravityamf" class="org.granite.gravity.channels.GravityChannel">
            <endpoint
                uri="http://{server.name}:{server.port}/{context.root}/gravityamf/amf"
                class="flex.messaging.endpoints.AMFEndpoint"/>
        </channel-definition>
    </channels>
</services-config>

4. Configure the Flex client application to use the topic

grails-app/view/flex/bookmanager.mxml

import org.granite.tide.data.DataObserver;
   
// Register a data observer component with the name of the topic
Spring.getInstance().addComponent("bookManagerTopic", DataObserver, false, true);
// Binds the subscribe and unsubscribe methods of the component to the application login/logout events
Spring.getInstance().addEventObserver("org.granite.tide.login", "bookManagerTopic", "subscribe");
Spring.getInstance().addEventObserver("org.granite.tide.logout", "bookManagerTopic", "unsubscribe");

5. Configure the controllers to handle dispatch of data updates

Just add the following annotation to all the controllers of the application :

@DataEnabled(topic="bookManagerTopic", params=ObserveAllPublishAll.class, publish=DataEnabled.PublishMode.ON_SUCCESS)

This references a parameter class that allows filtering of which update events can be dispatched. Here we will use an extremely simple filter class that filters nothing :

src/groovy/ObserveAllPublishAll.groovy

import org.granite.tide.data.DataObserveParams;
import org.granite.tide.data.DataPublishParams;
import org.granite.tide.data.DataTopicParams;

public class ObserveAllPublishAll implements DataTopicParams {

    public void observes(DataObserveParams params) {
        // Define key/value pairs that the client is able to observe
        // Will be used to construct the topic selector for the client calling the component
    }

    public void publishes(DataPublishParams params, Object entity) {
        // Define key/value pairs to add in the published message headers
        // Will be used to match against the topic selector of the subscribed clients
    }
}

Part 4 : Deploy all this as a war in Tomcat

Just run :

grails war

Then rename the generated bookmanager-0.1.war to bookmanager.war and copy it to the Tomcat webapps folder.
Ensure you have correctly installed the native APR connector, start Tomcat, and browse http://localhost:8080/bookmanager/bookmanager.swf, et voilà !


I will stop here for this article. We could go a bit further by adding conflict handling, or per-instance authorizations, but I let this for a future post.
Hopefully this article has shown the range of capabilities of the plugin and of the underlying GraniteDS Flex/Java integration library.

As always, don't hesitate to experiment all this and give your feedback.

Building a Flex multi-tab CRUD application : adding security and server push

The first part of this article has described how to build the main application. The goal of this second part is to demonstrate how you can easily add security and collaborative updates to this existing application with the gdsflex 0.3 Grails plugin.

Before anything, we need to upgrade the previous project to the latest gdsflex plugin release 0.3 with :

grails install-plugin gdsflex

The usual way of adding security to a Grails application is to use the Acegi/Spring security Grails plugin. So now we have to setup this plugin.

grails install-plugin acegi

grails create-auth-domains User Role Requestmap

grails generate-manager

This will install the plugin and generate a set of gsp pages to create roles and users. Now browse http://localhost:8080/gdsexample/role/create, and create 2 roles ROLE_ADMIN and ROLE_USER. Then http://localhost:8080/gdsexample/user/create, and create 2 users admin and user, each one with one of the previously created roles. The names of the roles are important for Spring security and have to start with 'ROLE_'.

We also have to enable the Spring security integration in the GraniteDS config file:

web-app/WEB-INF/granite/granite-config.xml, uncomment or add the following line:

<security type="org.granite.messaging.service.security.SpringSecurityService"/>

Once this setup is done, we have to define a login page in the Flex application. To do this, we will simply add a ViewStack in the main MXML that will display either the login page or the application depending on the user login state. This ViewStack will be bound to the Tide Identity component that handles user authentication :

grails-app/views/GDSExample.mxml :

<?xml version="1.0" encoding="utf-8"?>

<mx:Application
   xmlns:mx="http://www.adobe.com/2006/mxml"
   xmlns="*"
   layout="vertical"
   backgroundGradientColors="[#0e2e7d, #6479ab]"
   preinitialize="Spring.getInstance().initApplication()">
 
   <mx:Script>
       <![CDATA[
           import org.granite.tide.spring.Spring;
           import org.granite.tide.validators.ValidatorExceptionHandler;
           import org.granite.tide.spring.Identity;
           import org.granite.tide.events.TideResultEvent;
           import org.granite.tide.events.TideFaultEvent;
         
           Spring.getInstance().addExceptionHandler(ValidatorExceptionHandler);
         
           [Bindable] [In]
           public var identity:Identity;
         
         
           [Bindable]
           private var message:String;
         
           private function loginResult(event:TideResultEvent):void {
               message = "";
           }
         
           private function loginFault(event:TideFaultEvent):void {
               message = event.fault.faultString;
           }
       ]]>
   </mx:Script>

   <mx:ViewStack id="appView" selectedIndex="{identity.loggedIn ? 1 : 0}" width="100%" height="100%">

       <mx:VBox width="100%" height="100%" verticalAlign="middle" horizontalAlign="center" >
           <mx:Panel title="Login"
               horizontalAlign="center"
               verticalGap="0" paddingTop="8" paddingBottom="8"
               xmlns:mx="http://www.adobe.com/2006/mxml">

               <mx:Form>
                   <mx:FormItem label="Username">
                       <mx:TextInput id="username"/>
                   </mx:FormItem>
                   <mx:FormItem label="Password">
                       <mx:TextInput id="password" displayAsPassword="true"
                           enter="identity.login(username.text, password.text, loginResult, loginFault);"/>
                   </mx:FormItem>
               </mx:Form>
             
               <mx:Label text="{message}"/>

               <mx:Button label="Login"
                   click="identity.login(username.text, password.text, loginResult, loginFault);"/>
           </mx:Panel>
       </mx:VBox>
     
       <mx:VBox id="mainUI" width="100%">
           <mx:ApplicationControlBar id="acb" width="100%">
               <mx:Label text="GraniteDS / Grails example" fontSize="18" fontWeight="bold" color="#f0f0f0"/>
               <mx:Button label="Logout" click="identity.logout()"/>
           </mx:ApplicationControlBar>
         
           <BookUI id="bookUI" width="100%" height="100%"/>
       </mx:VBox>
     
   </mx:ViewStack>
</mx:Application>

As you can see, most of the code we have added is the login form. The authentication is completely handled by the Identity component. Here we make use of its two main methods login / logout and of its loggedIn property that is bindable and is here used to select which view is displayed. We also define a fault handler to display a login error message when the entered credentials are not correct.

You can check now on http://localhost:8080/gdsexample/GDSExample.swf that only authenticated people can see and change existing data.

To further refine the security of the application, we could decide that only administrators are allowed to delete books in our database. This can be done server-side with Spring security, but here we'll just see how to modify the UI according to the user access rights. This is not enabled by default in the plugin, we just have to change the plugin settings, and add a GraniteDSConfig.groovy in grails-app/conf:

grails-app/conf/GraniteDSConfig.groovy :

graniteConfig {

  springSecurityAuthorizationEnabled = true

}

Then we have to make a few changes in the MXML UI to hide the Delete button when the user is not an administrator:

grails-app/views/BookEdit.mxml :

           import org.granite.tide.spring.Identity;
         
           [Bindable] [In]
           public var identity:Identity;
     
     
       <mx:HBox>
           <mx:Button label="Save" click="save()"/>
           <mx:Button label="Delete"
               enabled="{!create}"
               visible="{identity.ifAllGranted('ROLE_ADMIN')}"
               click="remove()"/>
           <mx:Button label="Cancel" click="cancel()"/>
       </mx:HBox>

You can check that if you don't log in with a user having the ROLE_ADMIN role, you don't have the Delete button. You should of course also enable server-side Spring security (for example with the @Secured annotation) and define a AccessDeniedExceptionHandler that would catch all security errors to display a uniform message (see the documentation or GDS/Tide/Spring example for more information).
The Identity component provides 4 bindable boolean methods ifAllGranted, ifNotGranted, ifAnyGranted and hasPermission corresponding to the JSP tags available in the Spring security tag library. The hasPermission is not supported right now by the Grails plugin but it depends on the configuration of Spring security ACLs that itself would probably require a complete article.

To finish this post, we will add real-time multiuser updates by adding the Gravity push functionality to our application. First we have to enable these functionalities in the plugin settings:

grails-app/conf/GraniteDSConfig.groovy :

graniteConfig {

  springSecurityAuthorizationEnabled = true

  gravityEnabled = true

  dataDispatchEnabled = false
}

Then we have to define a Gravity channel and topic in the services-config.xml Flex configuration:

web-app/WEB-INF/flex/services-config.xml:

<services-config>

    <services>
        <service id="granite-service"
            class="flex.messaging.services.RemotingService"
            messageTypes="flex.messaging.messages.RemotingMessage">
   
            <destination id="spring">
                <channels>
                    <channel ref="my-graniteamf"/>
                </channels>
                <properties>
                    <factory>tideSpringFactory</factory>
                    <persistenceManagerBeanName>tidePersistenceManager</persistenceManagerBeanName>
                </properties>
            </destination>
        </service>
        
        <service id="gravity-service"
            class="flex.messaging.services.MessagingService"
            messageTypes="flex.messaging.messages.AsyncMessage">
            <adapters>
                <adapter-definition id="simple" class="org.granite.gravity.adapters.SimpleServiceAdapter"/>
            </adapters>

            <destination id="bookManagerTopic">
                <properties>
                  <session-selector>true</session-selector>
                </properties>
                <channels>
                    <channel ref="my-gravityamf"/>
                </channels>
                <adapter ref="simple"/>
            </destination>
        </service>
    </services>

    <factories>
        <factory id="tideSpringFactory" class="org.granite.tide.spring.SpringServiceFactory">
        </factory>
    </factories>

    <!--
     ! Declares my-graniteamf channel.
     !-->
    <channels>
        <channel-definition id="my-graniteamf" class="mx.messaging.channels.AMFChannel">
            <endpoint
                uri="http://{server.name}:{server.port}/{context.root}/graniteamf/amf"
                class="flex.messaging.endpoints.AMFEndpoint"/>
        </channel-definition>
        
        <channel-definition id="my-gravityamf" class="org.granite.gravity.channels.GravityChannel">
            <endpoint
                uri="http://{server.name}:{server.port}/{context.root}/gravityamf/amf"
                class="flex.messaging.endpoints.AMFEndpoint"/>
        </channel-definition>
    </channels>

</services-config>

Here we have just added a new channel-definition, gravity-service and topic destination in the configuration, now we have to tell the Flex client and the Grails components to send/receive the data updates on this topic. The server part is relatively simple, we just have to annotate our controllers/services with the DataEnabled annotation:

@DataEnabled(topic="bookManagerTopic", params=ObserveAllPublishAll.class, publish=DataEnabled.PublishMode.ON_SUCCESS)

This annotation specifies the topic and has two other important parameters:

- 'params' defines a publishing selection class. To keep things simple here, we will just write a very simple selection class that allow everyone to observer and publish all updates. For some reason, using Groovy classes in annotations triggers an infinite loop in the Grails compilation, so we will just write a Java class this time:

src/java/ObserveAllPublishAll.java

import org.granite.tide.data.DataObserveParams;
import org.granite.tide.data.DataPublishParams;
import org.granite.tide.data.DataTopicParams;

public class ObserveAllPublishAll implements DataTopicParams {

 public void observes(DataObserveParams params) {
        // Define key/value pairs that the client is able to observe
        // Will be used to construct the topic selector for the client calling the component
 }

 public void publishes(DataPublishParams params, Object entity) {
        // Define key/value pairs to add in the published message headers
        // Will be used to match against the topic selector of the subscribed clients
 }
}

- 'publish' defines the publishing mode. ON_SUCCESS indicates that all remote calls on annotated components that do not trigger exceptions will dispatch the corresponding entity updates. In general you will want to have more control on the dispatching and use the MANUAL mode to be sure that updates are dispatched only on transaction success and include the dispatch in a Grails interceptor. We could also have used a transactional JMS topic to have a real transactional behaviour. Let's keep it simple for this example.

On Flex side, you then have to add the data observer component in the main MXML:

grails-app/views/GDSExample.mxml :

            import org.granite.tide.data.DataObserver;
   
            // Register a data observer component with the name of the topic
            Spring.getInstance().addComponent("bookManagerTopic", DataObserver);
            // Binds the subscribe and unsubscribe methods of the component to the application login/logout events
            Spring.getInstance().addEventObserver("org.granite.tide.login", "bookManagerTopic", "subscribe");
            Spring.getInstance().addEventObserver("org.granite.tide.logout", "bookManagerTopic", "unsubscribe");
            
            [In]
            public var bookManagerTopic:DataObserver;

An interesting thing here is how you can bind a Tide event to any Tide component method, allowing for a complete decoupling between the component and the application.

Now if you open two browsers on the Flex application (in different http sessions, so for example you can try with one Firefox and one Internet Explorer, or better on two different machines), you can check that updates saved on one browser are (almost) immediately visible on the other.

If you look at the console, you will most likely see a lot of error stack traces concerning some RetryRequest error. This has something to do with some Grails filter logging the Jetty continuation retry exception. That's not extremely important, and it will be addressed in a later release. These configuration aspects of Gravity and other advanced features will also be improved to avoid having many places where to change configuration and centralize most of it in the GraniteDSConfig.groovy file.


Now we've seen a simple use of most features of GraniteDS. The complete project is available [here|http://www.graniteds.org/confluence/download/attachments/9371677/gdsexample-0.3.zip] and can be unzipped after having created the project and installed the various plugins (also remember to create roles and user otherwise you won't be able to log in).
We could have implemented the server side with any other Java server technology supported out-of-the-box by GDS/Tide (JBoss Seam, Spring, EJB3) with minimal change on the Flex side, but the Grails/GraniteDS combination seems a good choice to quickly develop Flex applications with a Java server backend.