In J2EE application modules are packaged as EAR, JAR and WAR based on their functionality
JAR: (Java ARchieve) EJB modules which contains enterprise java beans class files and EJB deployment descriptor are packed as JAR files with .jar extenstion
WAR: (Web application ARchive)Web modules which contains Servlet class files,JSP FIles,supporting files, GIF and HTML files are packaged as JAR file with .war (web archive) extension
EAR: (Enterprise ARchive)All above files (.jar and .war) are packaged as JAR file with .ear (enterprise archive) extension and deployed into Application Server.
