Struts Tips #3

Developing a Java web application (especially in Struts) is different in many ways from developing in ColdFusion, ASP or even ASP.NET. One of the major differences is the structure of the application; generally ColdFusion, ASP and ASP.NET applications are structured around the file system; you end up at http://www.myhost.com/corporate/default.asp or http://www.myhost.com/products/default.cfm. One of the core ideas of Struts is the idea of mapping an action (/cart/checkout/billing) to an Action class (com.myhost.cart.checkout.Billing), the file system doesn’t really come into play. Another variation is the way in which applications are normally deployed (or at least the way I’ve seen them deployed): ASP, ColdFusion and ASP.NET applications are generally deployed at the root of a website while Java web applications introduce the idea of a ‘context’, where the context can be the root (context = “”) or the context can be something else (context = “/store”).

These two differences lead to a major problem if you’re creating web applications with Struts: instead of being able to reference an image using an absolute path like this:
<img src="/images/logo.jpg" />
you need to reference your images using a relative path like this:
<img src="images/logo.jpg" />
But wait! You can’t do that either because the URL of your page could /cart/checkout/billing.do or /products/cars/accessories.do, both of which could be deployed to different servlet context (“/store” for instance). If you used a relative path and then visited a page like /cart/checkout/billing.do, the webserver would request the image from /cart/checkout/images/logo.jpg, which is most likely not where you have it located.

Luckily, the Struts team put together the tag (for images) and the associated tag (for image buttons). The tags are pretty easy to pick and use. Putting an image on a page is going to take the form of:
<html:img src="/images/logo.jpg" />
or
<html:img page="/images/logo.jpg" />
The first one won’t help much in the context of this discussion; it has the exact same problems as using a regular old <img src="..." /> tag, except that the URL will be rewritten for users that don’t accept cookies. The second option is much more useful. If you use the page attribute instead of the src attribute, the “…image will automatically prepend the context path of this web application (in the same manner as the page attribute on the link tag works), in addition to any necessary URL rewriting. (src)”

Using the <html:image /> tag is really no different, so I won’t get into it (it generates an <input type="image" ... /> tag), other than to mention that it doesn’t accept height or width attributes and it doesn’t (like all JSP tag attributes) pass them through to the generated tag, which could cause problems if you migrate all your <input type="image" .../> tags over to <html:image />.

In short, if you’re developing a Struts application, make sure to familiarize yourself with all the tags, doing so can save you alot of time when your boss decides that the application should be deployed in a different servlet context.

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