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JSP best practices

Follow these tips for reusable and easily maintainable JavaServer Pages

By Dustin Marx, JavaWorld.com, 11/29/01

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Include action

The include action executes the specified JSP first and then places the generated response in the calling JSP. Because the include action includes the generated response rather than the source content itself, variables and other values specified in the calling JSP are not available to the page included with the include action.

One disadvantage of the include action as currently implemented by the JSP implementations with which I am familiar relates to the flush="true" attribute. In the JSP implementations I have used, this attribute is required and must be set to true. The true value indicates that the buffer will always flush before a target page specified by the include action executes. This can prove problematic if the forward mechanism is invoked either explicitly or implicitly later in the JSP. In the recently released JSP specification (1.2), however, the include action's flush attribute can be set to false. Tomcat 4.0 provides a reference implementation of this specification and supports this new include action argument.

Use a JSP template mechanism

A template mechanism allows for a common file to control Webpage, or JSP, layout. Then, when you want to change the layout, you need to modify only one file, and all the other pages will reflect the layout change. This doesn't just make for more maintainable code; using templates to control layout also makes Webpages more aesthetically pleasing to users who see consistent layouts for all an application's pages.

I use Struts' custom tag template library as a template mechanism. David Geary's article "JSP Templates" provides a good starting point for looking at using templates with your JSPs.

Use stylesheets

Just as templates enable developers to place layout control in a single location, stylesheets enable developers to place appearance control in a single location. I use Cascading Style Sheets (CSS) to control such items as font families, font sizes, and table characteristics. Like templates, stylesheets allow the developer to make changes in one location; those changes immediately reflect on all appropriate pages, resulting in increased maintainability and consistent appearance to users.

Use the MVC pattern

While other design patterns can be used effectively with JSPs, I often use the Model-View-Controller (MVC) architecture with JSP technology. MVC enables the development of applications that are easier to create, test, maintain, and enhance. In JSP terminology, implementation of an MVC architecture is often referred to as Model 2 (from an early JSP specification). The J2EE Blueprints samples are based on MVC.

See "E++: A Pattern Language for J2EE Applications, Part 1" by Bin Yang, and "Understanding JavaServer Pages Model 2 Architecture" by Govind Seshadri, for more information on JSPs and MVC.

Struts

Struts is an open source MVC implementation (it's a Jakarta subproject available through the Apache license) that provides base controller functionality that you can extend and enhance in your own applications. The base controller is implemented as a Java servlet, and its configuration is controlled by an XML file called struts-config.xml. When a Struts-based JSP Web application is created correctly, most changes in flow control are made in the struts-config.xml file rather than in the code itself.

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