Why does the project's jar package conflict with the Tomcat jar package?

Why does the project's jar package conflict with the Tomcat jar package?

Encounter this problem, guess Tomcat start will be their Lib and the project Lib logically merged into a large lib, but did not make version and go to heavy, so that the same package may have two references, start naturally do not know which package, which will lead to conflict. Purely guessing, and then adding corrections after studying Tomcat's loading process. Before I downloaded how Tomcat works.pdf had time to look, it should be able to answer all the questions, in plain English.

Next is tomcat\lib under the package, box out is easy accidentally two times introduced the package, attention is good.

Why does the project's jar package conflict with the Tomcat jar package?