I would like to know if it is possible to load a custom class out side the .war.
Is it a good solution to minimus the redeploy times of our system -_-. Is there any class loading, class update issue( when each servlet instance uses it) ??
As long as the class you want to load from your servlet is in the classpath for the servlet, it doesn't matter if the class is in the .war or not. Try adding the class to your system classpath or depending what container you're using (WebLogic, JBoss etc.) add it to the application classpath.
For a Tomcat installation, you would include the .class files (or packaged .jar file) in the <Tomcat_Home>/common/lib directory or the <Tomcat_Home>/shared/lib directory.
I'm sure there are similar setups for others.