Last December, SpringSource and Adobe announced a partnership aimed at streamlining the integration between Spring and BlazeDS. This partnership has led to the new Spring BlazeDS Integration project, which allows you to seamlessly integrate the two technologies and build state-of-the-art Internet applications that feature a Flex front end and a Spring back end.
Whether you are a Flex developer just learning Spring or a Spring developer learning Flex, you can benefit from the powerful integration of these technologies.
Spring has emerged as the de facto standard for building the Java back end of Internet applications. Flex is rapidly becoming the preferred technology for building innovative Internet applications delivered in the browser and on the desktop (using the Adobe AIR runtime).
This article provides an introduction to the Spring BlazeDS Integration, and includes a simple example application to illustrate key concepts.
What is Spring?
The foundation of the Spring framework is a lightweight component container that implements the Inversion of Control (IoC) pattern. Using an IoC container, components don't instantiate or even look up their dependencies (the objects they work with). The container is responsible for injecting those dependencies when it creates the components (hence the term "Dependency Injection", which is also used to describe this pattern).
By enabling looser coupling between components, the Spring IoC container has proven to be a solid foundation for building robust enterprise applications.
The components managed by the Spring IoC container are called Spring beans. In addition to its core IoC container, The Spring framework includes several other modules, including support for transaction management, JDBC Data Access, and ORM Data Access. While these modules are beyond the scope of this article, it is important to note that an additional benefit of using BlazeDS with Spring is the ability to leverage these modules to facilitate the development of your remote objects. More information on the Spring framework can be found here.
What is Flex?
Flex is an environment for building Rich Internet Applications. The Flex programming model includes:
- ActionScript - an ECMAScript-compliant, object-oriented programming language. With some syntactical differences, ActionScript looks and feels similar to Java, and supports the same object-oriented constructs: packages, classes, inheritance, interfaces, strong (but also dynamic) typing, and so on.
- MXML - an XML-based language that provides an abstraction on top of ActionScript, and allows parts of an application (typically the View) to be built declaratively.
- An extensive set of class libraries. The documentation is available here in Javadoc-like format.
The Flex source code (.mxml and .as files) is compiled into Flash bytecode (.swf) that is executed at the client side by the ActionScriptVirtual Machine in Flash Player using a Just-In-Time compiler.
The Flex SDK is an open-source project. It includes the Flex component library, the compiler, the debugger, and the documentation. A complete discussion of Flex is beyond the scope of this article, but you can find more information and download the Flex SDK here.
What is BlazeDS?
BlazeDS is a set of data services that give your Flex applications additional options for data connectivity. Without BlazeDS (or, without deploying any Flex-specific component on the server side), Flex applications can access back-end data using either the HTTPService or WebService components:
- You use the HTTPService component to send HTTP requests to a server and consume the response. Although the HTTPService is often used to consume XML, it can be used to consume responses in other formats, including JSON. The Flex HTTPService is similar to the XMLHttpRequest component available in Ajax.
- You use the WebService component to invoke SOAP-based web services.
BlazeDS adds the following services:
- The Remoting Service allows your Flex application to directly invoke methods of Java objects deployed in your application server.
- The Message Service provides a publish/subscribe infrastructure that enables your Flex application to publish messages and subscribe to a messaging destination, enabling the development of real-time data push and collaborative applications.
- The Proxy Service allows your Flex application to make cross-domain service requests in a secure and controlled manner. In other words, it allows your Flex application to access a service available on a different domain than the domain from where the application was downloaded (without having to deploy a crossdomain.xml policy file on the target domain).
BlazeDS is deployed as a set of JAR files as part of your web application. Like the Flex SDK, BlazeDS is an open-source project. More information is available here.