Flex: The World's Simplest Example of RemoteObject

Here is a very, very simple example of using the RemoteObject RPC services in Flex 2 to invoke methods on a Java object. I came up with this because I was struggling to figure out all the stuff needed to do this. In theory, it's pretty simple, but there are a number of components to deal with, and they all get put in different places on the server, and a bunch of those places look very similar to other places on the server.

Introduction

It was especially difficult for me because I'm new to Flex, and I'm coming at it from a server-side background in Java. I don't care about making pretty user interfaces (that's someone else's job) - I'm the guy who has to make the server code work. However, most of the documentation assumes that you're coming at it from the other end - the client side.

I couldn't find any simple examples of using RPC in Flex 2.0. I foolishly started with Flex 1.5 example and wasted a bunch of time updating the syntax in it in order to get it to compile.

After I got that to compile (from the command line - I'm old school), it wouldn't run. After I got the Flash debugger working, I could see that the messaging destination didn't exist, but I couldn't figure out why. So far as I could tell, I had configured it correctly, but there was no indication that things were making it to the server. Finally, I gave up my command line and put the MXML file on the server, and just let the web-tier compiler do it for me.

And, it just worked! The documentation makes reference to using the SDK compiler versus the web-tier compiler, but it just didn't click with me. But, it was still more complicated than I needed. So, I created the following, to prove that I could do it, and that I knew all the voodoo needed.

I will assume that you have the Flex Data Services demo server with Jrun installed an running. I will specify all paths from the root of the jrun server.

Java Code

Let's start with the simplest function in a Java file - basically, "hello world."

public class SimpleRemoteObject
{
 public void writeToConsole(String msg)
 {
     System.out.println("SimpleRemoteObject.write: " + msg);
 }
}

This will just write a message to the server console window. (We don't even have to use any fancy Java logging.)

Compile that file and put the SimpleRemoteObject.class file in the directory jrun4/servers/default/samples/WEB-INF/classes on the server. (Note that since the class is in the unnamed, default package, we put the class file in classes, not a subdirectory.)

Flash Client

Now, we need a simple Flash app. Here's a simple MXML file:

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
 backgroundColor="#FFFFFF"
 initialize="initApp()">
 <mx:Script>
     public function initApp():void {
     }

     public function writeToConsole():void {
         remoteObj.writeToConsole("hello from Flash client");
     }
 </mx:Script>

 <mx:RemoteObject id="remoteObj" destination="sro">
     <mx:method name="writeToConsole"/>
 </mx:RemoteObject>

 <mx:Form>
     <mx:FormItem>
         <mx:Button label="Write To Server Console" click="writeToConsole()"/>
     </mx:FormItem>
 </mx:Form>
</mx:Application>

Create a directory called sro under jrun4/servers/default/samples and put the MXML file there.

Now, we can compile the file by loading it in the browser with a URL like:
http://192.168.123.130:8700/samples/sro/SimpleRemoteObject.mxml
(The key is that the file is under /samples/sro based on where we copied the file.)

Don't click the button yet! We still have to configure the FMS destination. Just make sure it compiles correctly.

Configure the Server

Add the following XML code to jrun4/servers/default/samples/WEB-INF/flex/remoting-config.xml. Just put it within the service tag for the remoting-service - e.g., near one of the other FMS destinations.

<destination id="sro">
 <properties>
     <source>SimpleRemoteObject</source>
 </properties>
</destination>

And now, if you press the "Write to Server Console" button, the message, "hello from Flash client" will appear in the Jrun server window.

That's it. It really is as easy as Adobe says it is...
once you figure it all out.

enjoy,
Charles.