The J2EE platform provides many supporting services that enhance the capabilities of web components and make them easier to develop. However, because it must take into account these services, the process for creating and running a web component is different than that of traditional stand-alone Java classes.
Web components run within an environment called a web container .
The web container provides services such as request dispatching, security, concurrency, and life cycle management. It also gives web components access to the J2EE platform APIs such as naming, transactions, and email. Certain aspects of web component behavior can be configured when it is packaged and deployed. The configuration information is maintained in a text file in XML format called a web application deployment descriptor . When you package and deploy web components using the J2EE SDK deploytool , it automatically generates or updates the deployment descriptor based on data that you enter in deploytool wizards and inspectors.