WADI (Web Application Distribution Infrastructure) is an HttpSession Manager that can be plugged into Tomcat or Jetty in order to provide distributed state management services. Its current primary focus is to manage and protect web tier state in a clustered environment as efficiently and economically as possible, without making the prohibitively expensive step of replicating it to either other vms or a database. Such functionality will soon be added, but should only be used in situations where extreme availability is perceived to be worth that price.
License: ASF 2.0
Project Site: http://wadi.codehaus.org
WADI 0.9 (binary & source 1 MB)
WADI FAQ Jules Gosnell (free!)

Open Source J2EE™ Web Tier

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User, Development and SCM mailing lists are maintained for this project.