Ask about Desgin Patterns in Tomcat

[Luong Dinh Hieu]

Dear Sir or Madam,

I would like to investigate how Design Patterns are used in Tomcat 
(particularly, in the directory java/org/apache/catalina). Can you give 
me any suggestions such that I can understand how Tomcat is organized, 
how it works and how Design Patterns are applied in Source Code?

Any suggestions or documents are appreciated. I'm looking forward to 
your response.
Thank You,

Best Regards,
HieuLD