How can I pass data from a servlet running in one context (webapp) to a servlet running in another context?

There are three ways I can think of off the top of my head:

1. Store the information you want to share in a persistant format, such as in a file system or database. That way, any servlet that is running in a JVM that can "see" these resources can get to this information.
2. If persisting this information is not an option, you can bind this information to a context that is accessible to all servlet contexts, such as the application server's context. This way, you can keep the data you want to share in memory.
3. Use the old fashion way of passing information to a servlet - HTTP. One servlet could foward a request to another servlet and include the data that needs to be shared as parameters in the request.

[See also http://www.jguru.com/jguru/faq/view.jsp?EID=50791]