From Farata Systems Flex Blog

My primary clients are Java shops. When I suggest using Adobe Flex 2 as a rich client tool for their Web applications, they typically ask about the cost on the server side.  Expected answer: free.

When I start telling them about really powerful features of Flex Data Services, they like it. They just do not like the licensing cost, which is very reasonable. But  Flex 2, it's too young, and some people are still in denial phase. It'll change soon, but there's got to be a free solution.  Just to get the foot in the door.  And there is one. 

I'll be using a JavaServer Page (JSP) here, but you can replace a JSP with any technology  you're comfortable with: servlets, Active Server Pages, Python, PHP et al. Whatever can spit out an XML to a Web browser should work the same way.

I'll show you a really simple application written in Flex 2 that talks to the XML producing JavaServer page. Just to make it simple, let's take  an XML with the information about employees:

<people>
  <person>
      <name>Alex Olson</name>
      <age>22</age><skills>java, HTML, SQL</skills>
  </person>
...
</people>

Now, let's hardcode this (I've got three persons) into a super simple JSP that consists of one out.println() call, where the xml should go between the double quotes:
<%out.println("..."); %>

The complete JSP looks like this (just put your XML in one line so you won't bother with string concatenations):
<%
out.println("<?xml version=\"1.0\" encoding=\"UTF-8\"?><people><person><name>Alex Olson</name><age>22</age><skills>java, HTML, SQL</skills></person><person><name>Brandon Smith</name><age>21</age><skills>PowerScript, JavaScript, ActionScript</skills></person><person><name>Jeremy Plant</name><age>20</age><skills>SQL, C++, Java</skills></person></people>");
%>

Deploy this JSP under some servlet container. I have Tomcat, so I just saved it as employees.jsp under my webapp\test  directory.  Do a sanity check to make sure that you've deployed this JSP correctly:  entering  http://localhost:8080/test/employees.jsp in your Web browser has to return the employee data.

Now comes the client part.  If you have an extra $500 laying around, purchase a license of Flex Builder from Adobe and enter the code below in its editor.  If you do not want to spend  any money,  just  type this code in any text editor and use the free command line mxmlc compiler that comes with Flex 2.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
                             applicationComplete="employees.send()">
    <mx:HTTPService id="employees" useProxy="false"  method="POST"
        url="http://localhost:8080/test/employees.jsp" />

    <mx:DataGrid  dataProvider="{employees.lastResult.people.person}" width="60%">
          <mx:columns>
            <mx:DataGridColumn dataField="name" headerText="Name"/>
            <mx:DataGridColumn dataField="age" headerText="Age"/>
            <mx:DataGridColumn dataField="skills" headerText="Skills"/>                       
         </mx:columns>
    </mx:DataGrid>
</mx:Application>
 
Not too much typing, isn't it?

This code uses the  <mx:HTTPService> component that allows you to connect to a specified URL either directly or through a proxy. In my example I just specify the URL of my JSP. The data provider of my data grid uses binding (see the curly braces) and E4X syntax to parse the XML and populate this table with the elements located under the <person>  XML tag that is coming from our employees.jsp. Next month, I'll write a piece explaining Flex data binding in more details.  On the applicationComplete event, we send a request to the  HTTPService object known under id employees, and our JSP readily returns the XML, which is bound to the data grid.

Compile and run this program, and it'll show you the following: