From website:

Esper is a component for CEP and ESP applications, available for Java as Esper, and for .NET as NEsper.

Esper and NEsper enable rapid development of applications that process large volumes of incoming messages or events. Esper and NEsper filter and analyze events in various ways, and respond to conditions of interest in real-time.




Tip for Windows users or non-java persons on how to view source code:
1.Install 7 zip utility. http://www.7-zip.org/
2.Download esper code from the above download link, and extract the folder.
2.After installing, do a search on .jar files in the folder. Select them all, and choose menu option "7 Zip->Extract files". This will unzip the .jar files into the destination folder
3.You cannot yet view source, as .class files are binary
4.Download java decompiler http://java.decompiler.free.fr/jd-gui/downloads/jd-gui-0.3.3.windows.zip
5. Run the java decompiler application, and open the .class files to view the source code