Programming Jakarta Struts

Using Definitions

The tiles shown so far add value to an application because they organize the layout of a page in a single resource, the layout JSP page. This can save development time and, more importantly, the time it takes to change the layout for an application. However, there is a problem with the approach used in the Storefront application shown earlier. In each of the non-layout tiles, there is redundant code that specifies what content to use for the header, menubar, and copyright content—the same attributes are being passed in every page. This may not always be the case, but in general, these values will be constant throughout an application. For instance, the same copyright is typically shown on every page.

It’s redundant to have to specify these in every tile. Ideally, we could declare these attributes in one place, and the tiles could include just the page-specific attributes where needed. Tiles definitions provide just such functionality. A definition allows you to statically specify the attributes that are used by a template, which in turn allows you to specify only the page-specific attributes in your tiles. Definitions enable you to:

• Screen definitions

• Centralize declaration of page description

• Avoid repetitive declaration of nearly identical pages (by using definition inheritance)

• Avoid creation of intermediate components used to pass parameters

• Specify the name of a definition as a forward in the Struts configuration file

• Specify the name of a definition as component ...