[news.eclipse.newcomer] Resource Not Available

[Gary Mrenak <gmrenak@xxxxxxxxxxxxxxxxxxx>]

Eclipse 3.2.2/Tomcat 5.5

Under the WebContent folder in a Web app I've created a simple jsp, and 
I 'test' it by right-clicking on the jsp > Run As > Run on Server.

When I've done this, I would get (occasionally, not always) error 404 
"Resource (...jsp) not available"  results, and these seemed 
unpredictable ... sometimes the jsp would be rendered correctly, at 
other times error 404.

However, for reasons I don't understand, I can make it perform correctly 
and reliably when I follow these steps:

1) Right-click on the jsp > Run As > Run on Server

Up comes the "Define a New Server" form of the "Run on Server" wizard 
dialog, with "Choose the type of server to create" selected and Tomcat 
highlighted .. I make no changes

2) Click 'Next'

Up comes the "Add and Remove Projects" form .. I make no changes

3) Click 'Next'

Up comes the "Select Tasks" form with the following task displayed: 
"Update context root for Web module to match the current settings" and a 
check box

If this check box is checked, then, when I click 'Finish', the jsp seems 
to be reliably rendered correctly (no error 404s).

Can someone explain the significance of "Update context root for Web 
module"?

Thanks,
Gary