Hot deployment and dynamic reloading
You can make various changes to applications and their contents without having to stop the server and start it again. Making these types of changes is known as hot deployment and dynamic reloading.
Hot deployment is the process of adding new components (such as WAR files, EJB Jar files, enterprise Java beans, servlets, and JSP files) to a running server without having to stop the application server process and start it again.
Dynamic reloading is the ability to change an existing component without needing to restart the server in order for the change to take effect. Dynamic reloading involves:
Changes to the implementation of a component of an application, such as changing the implementation of a servlet
Changes to the settings of the application, such as changing the deployment descriptor for a Web module
If the application you are updating is deployed on a server that has its application class loader policy set to SINGLE, you might not be able to dynamically reload your application. At minimum, you must restart the server after updating your application.