jXLS is a small and easy-to-use Java library for writing Excel files using XLS templates and reading data from Excel into Java objects using XML configuration.

Surprisingly common scenarios:

• requiring 1G memory to support a few hundred users
• saving 500K session state per user
• requiring 2M for a text index per simple document
• creating 100K temporary objects per user hit

This covers the basics of memory allocation and garbage collection in Java, the different garbage collectors available in HotSpot and how they can be tuned, and finally some anecdotes from Attila’s experiences at Twitter.

Distributed and fault-tolerant realtime computation: stream processing, continuous computation, distributed RPC, and more

How to redefine the cached values of Integers between -127 and 128 in Java.

Clojars is a dead easy community repository for open source Clojure libraries. It plays nice with Maven and Leiningen.