there is some websites available to learn:
http://www.cnblogs.com/wannaCNBLOGS/archive/2006/02/10/328467.html
http://sdt.sumida.com.cn:8080/cs/blogs/jawance/archive/2006/12/22/working-with-httpcontext-current.aspx
http://openmymind.net/index.aspx?documentId=6#context