Why Tomcat

I wanted to execute a code written in Java rather than PHP or JS on the server side. I came to know that tomcat is a server that understand how to execute Java code on the server side and does it with the help of servlets. That's the way I landed into this world of Java servlets and tomcat otherwise PHP/JS is my favorite language to be used at server-side. To be frank, I have never used other than these two language on the server-side so far. If you are also going to start on java servlets like me, i am using the tutorial here and its nice - - http://www.tutorialspoint.com/servlets/servlets-environment-setup.htm