J2EE Interview questions and answers

7. What are the differences between Ear, Jar and War
files? Under what circumstances should we use each
one?

There are no structural differences between the files;
they are all archived using zip-jar compression.
However, they are intended for different purposes.
--Jar files (files with a .jar extension) arre
intended to hold generic libraries of Java classes,
resources, auxiliary files, etc.
--War files (files with a .war extension) arre
intended to contain complete Web applications. In this
context, a Web application is defined as a single
group of files, classes, resources, .jar files that
can be packaged and accessed as one servlet context.
--Ear files (files with a .ear extension) arre
intended to contain complete enterprise applications.
In this context, an enterprise application is defined
as a collection of .jar files, resources, classes, and
multiple Web applications.
Each type of file (.jar, .war, .ear) is processed
uniquely by application servers, servlet containers,
EJB containers, etc.