You use ServletContext if you want your object visible to all the clients of the web application installed in a container. These objects remain there for the life of the application and can be shared with other servlets.
The ServletContext basically represents your web application. This is where your servlets "live." So, as Todd said, you can share data among your servlets by setting attributes on the ServletContext. ServletContext attributes are web application-wide. They are not specific to any one user (for that use HTTPSession attributes). They are not specific to any one request (for that use ServletRequest attributes).
James Carman, President<br />Carman Consulting, Inc.