Integrating Adobe Flex with Struts 2

I have noticed a lot of people on the internet are searching for information on how to integrate Struts 2 with Adobe Flex. It is not as complicated as most think and there's more than one way of doing it.

Ways in which you can integrate Adobe Flex and Struts:

1. Use HttpService in Adobe Flex to call actions in Struts. In Struts, instead of returning a jsp file change the return type of your action to XSLT. In this way the contents of your action are automatically converted to XML. You can use the XML result in Adobe Flex to determine the result of the action that you invoked using HttpService.
This technique is by far the easiest of the three.
The main advantages are:

• It is quite simple to use compared to the other techniques


• You get complete control on the information that you transfer between Adobe Flex and Struts

There are disadvantages though:

• The more information you transfer between Flex and Struts the more code you have to write for parsing/converting/... data

You can easily use HttpService to register a user using a struts action or to authenticate a user. Or you can use HttpService to retrieve information from the database through struts. In my next post I will give you an example on how to implement a registration system using HttpService.

2. Use Soap Web Services

Use Soap WebServices to connect to the Struts 2 backend. If you use an EJB 3 compliant application server you can easily create a web service by adding the @WebService annotation to an EJB 3 bean interface.
If you don't have an EJB 3 compliant application server we recommend you to use Apache Axis 2 or Enunciate. The advantage of Enunciate is that you can publish your service not only for use with SOAP, it also creates endpoints for REST, AMF and JSON. We will exemplify this approach in a later post.

The advantages of using Web Services are:

• Automatic class generation: With a few mouse clicks and the WSDL that describes your web service, Flex generates all the classes needed to access your web service.
  This is done via the ported version of Apache Axis.


• The conversion of data from/to XML is done automatically for you. You only deal with objects and method calls.
  

The major disadvantage of using web services are circular references. An example of a circular reference is one where the child node of an object references its parent.

A ----> B
B ----> A

You need to deal with this by using annotations or by manually deleting the circular reference. Otherwise you will get a nasty marshaling/unmarshaling exception when calling the web service.

3. Using BlazeDS, from Flex it is possible to invoke methods on java objects deployed in an application server. This is done using AMF a message protocol developed by Adobe. This is a similar method to using SOAP. The only difference is that all the information is transferred in binary format. Performance wise this is probably the best option available to integrate Java/J2EE and Adobe Flex. Read my post on Integrate Adobe Flex and JBOSS using BlazeDS for more information.