web applications - What is web.xml file and what are all things can I do with it?

Question

The web.xml Deployment Descriptor Elements in Oracle's BEA WebLogic Server 8.1 Documentation pretty much sums up each element in a web.xml file. But I am also curious about points below:

1. Is there any configuration parameter which should be avoided like plague?
2. Any parameters related to performance or memory usage?
3. Security related risk due to common mis-configuration?

What else should I know about web.xml apart from element names and their usage?

Answer 1

What is web.xml file and what all things can I do with it ?

The /WEB-INF/web.xml file is the Web Application Deployment Descriptor of your application. This file is an XML document that defines everything about your application that a server needs to know (except the context path, which is assigned by the Application Deployer and Administrator when the application is deployed): servlets and other components like filters or listeners, initialization parameters, container-managed security constraints, resources, welcome pages, etc.

Note that reference you mentioned is pretty old (Java EE 1.4), there have been few changes in Java EE 5 and even more in Java EE 6 (which makes the web.xml "optional" and introduces Web Fragments).

Is there any configuration parameter which should be avoided like plague?

No.

Any parameters related to performance or memory usage?

No, such things are not configured at the application level but at the container level.

Security related risk due to common mis-configuration ?

Well, if you want to use container-managed security constraints and fail at configuring them properly, resources won't obviously be properly protected. Apart from that, the biggest security risks come from the code you'll deploy IMO.