I there any way to configure a shared external library location for multiple J2ee based web application which deployed in tomcat.
Place the shared libraries in Tomcat's common/lib
folder, and they will be available for all the webapps deployed on that server.
However, please note that deploying multiple applications on a single Tomcat server is considered bad practice. Tomcat is very lightweight, so running one instance per application is perfectly acceptable from a performance point of view. Also, it allows you to fine-tune Tomcat's memory, configuration, librairies, etc. differently for each web application.