TITLE: Patterns in Flexible Server Application Frameworks AUTHOR: James C. Hu [primary contact] jxh@entera.com ADDRESS: Entera, Inc. Attn: James Hu 40971 Encyclopedia Cr. Fremont, CA 94538 PHONE: 510 770 5215 (work) 510 791 6412 (home) AUTHOR: Christopher D. Gill cdgill@cs.wustl.edu ABSTRACT: This article describes a collection of patterns that re-occur in the design of flexible server application frameworks. These patterns are organized into three categories, corresponding to distinct architectural levels of scale: foundation, scaffolding, and framework. In addition to identifying well-known patterns at each of these levels, this article describes three new patterns: the Concrete Bridge pattern at the foundation level, and the Library and Strategized Concurrency State patterns at the framework level.