what is difference between TOMCAT SERVER and J2EE SERVER???

TOMCAT server is a web container for servlet and jsp. Where servlets live there life cycle. It maintain the hole life cycle of servlet and jsp. Means initialization, running and destroy. And a J2EE server is server which has more than features form Tomcat server. Every J2EE server contains a web container, EJB container, JMS(Java Message Service), database management(Connection pooling), JNDI, and many more things.

Tomcat is a servlet container developed by Apache Software Foundation. J2EE has more tools than Tomcat and is more complex. J2EE is more suitable if you want to use EJB(Enterprise Java Beans). Else go for Tomcat because it is simpler.