MVC web framework

Spring includes a powerful and highly configurable MVC web framework.

Spring's MVC model is most similar to that of Struts, although it is not derived from Struts. A Spring Controller is similar to a Struts Action in that it is a multithreaded service object, with a single instance executing on behalf of all clients. However, we believe that Spring MVC has some significant advantages over Struts. For example:

• Spring provides a very clean division between controllers, JavaBean models, and views.
• Spring's MVC is very flexible. Unlike Struts, which forces your Action and Form objects into concrete inheritance (thus taking away your single shot at concrete inheritance in Java), Spring MVC is entirely based on interfaces. Furthermore, just about every part of the Spring MVC framework is configurable via plugging in your own interface. Of course we also provide convenience classes as an implementation option.
• Spring, like WebWork, provides interceptors as well as controllers, making it easy to factor out behavior common to the handling of many requests.
• Spring MVC is truly view-agnostic. You don't get pushed to use JSP if you don't want to; you can use Velocity, XLST or other view technologies. If you want to use a custom view mechanism - for example, your own templating language - you can easily implement the Spring View interface to integrate it.
• Spring Controllers are configured via IoC like any other objects. This makes them easy to test, and beautifully integrated with other objects managed by Spring.
• Spring MVC web tiers are typically easier to test than Struts web tiers, due to the avoidance of forced concrete inheritance and explicit dependence of controllers on the dispatcher servlet.
• The web tier becomes a thin layer on top of a business object layer. This encourages good practice. Struts and other dedicated web frameworks leave you on your own in implementing your business objects; Spring provides an integrated framework for all tiers of your application.

As in Struts 1.1 and above, you can have as many dispatcher servlets as you need in a Spring MVC application.

The following example shows how a simple Spring Controller can access business objects defined in the same application context. This controller performs a Google search in its handleRequest() method:

public class GoogleSearchController
		implements Controller {

	private IGoogleSearchPort google;

	private String googleKey;

	public void setGoogle(IGoogleSearchPort google) {
		this.google = google;
	}

	public void setGoogleKey(String googleKey) {
		this.googleKey = googleKey;
	}

	public ModelAndView handleRequest(
				HttpServletRequest request, HttpServletResponse response)
		throws ServletException, IOException {
		String query = request.getParameter("query");
		GoogleSearchResult result =
			// Google property definitions omitted...

			// Use google business object
			google.doGoogleSearch(this.googleKey, query,
				start, maxResults, filter, restrict,
				safeSearch, lr, ie, oe);

		return new ModelAndView("googleResults", "result", result);
	}
}

In the prototype this code is taken from, IGoogleSearchPort is a GLUE web services proxy, returned by a Spring FactoryBean. However, Spring IoC isolates this controller from the underlying web services library. The interface could equally be implemented by a plain Java object, test stub, mock object, or EJB proxy, as discussed below. This controller contains no resource lookup; nothing except code necessary to support its web interaction.

Spring also provides support for data binding, forms, wizards and more complex workflow. A forthcoming article in this series will discuss Spring MVC in detail.

If your requirements are really complex, you should consider Spring Web Flow, a powerful framework that provides a higher level of abstraction for web flows than any traditional web MVC framework, and was discussed in a recent TSS article by its architect, Keith Donald.

A good introduction to the Spring MVC framework is Thomas Risberg's Spring MVC tutorial (http://www.springframework.org/docs/MVC-step-by-step/Spring-MVC-step-by-step.html). See also "Web MVC with the Spring Framework" (http://www.springframework.org/docs/web_mvc.html).

If you're happy with your favourite MVC framework, Spring's layered infrastructure allows you to use the rest of Spring without our MVC layer. We have Spring users who use Spring for middle tier management and data access but use Struts, WebWork, Tapestry or JSF in the web tier.