What are different main elements of deployment descriptor ?

Servlet

servlet 

• servlet-name 
• Unique name of servlet for the Web application

• servlet-class 
• Fully qualified class name of the servlet

• init-param 
• Key / value pair as an initialization param of the servlet

servlet-mapping (servlet-name , url-pattern)

• Mapping between a servlet and a URL pattern 
• servlet-name 
• Unique name of servlet 
• url-pattern 
• URL pattern of the mapping
  

Example
<servlet>
    <servlet-name>MyFrontControllerServlet</servlet-name>
    <display-name>MyFrontControllerservlet</display-name>
    <description>The main servlet</description>
    <servlet-class>
         com.demo.MyFrontControllerServlet 
    </servlet-class>
    <init-param>
         <param-name>xml</param-name>
         <param-value>/WEB-INF/conf/myapp.xml</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
</servlet>
 
<servlet-mapping>
    <servlet-name>MyFrontControllerServlet</servlet-name>
    <url-pattern>/myapp/*</url-pattern>
</servlet-mapping>


Servlet context
Servlet Context init parameters
context-param (param-name, param-value, description) 

• Key / value pair as an initialization param associated with the web application 
• Each parameter name must be unique in the web application 
• These can be accessed in servlet by : 
• ServletContext.getInitParameter
• ServletContext.getInitParameterNames
  

Example
<web-app>
  <context-param>
     <param-name>Webmaster</param-name>
     <param-value>webmaster@mycorp.com</param-value>
  </context-param>
</web-app>
 

Filter
filter

• filter-name 
• Unique name of filter for the Web application

• filter-class 
• Fully qualified class name of the filter

• init-param 
• Key / value pair as an initialization param of the filter

filter-mapping (servlet-name , url-pattern)

• Mapping between a filter and resource (servlet / JSP)
• filter-name 
• Unique name of filter
• servlet-name
• Name of servlet to be wrapped by the filter

Example
<filter>
  <filter-name>HibernateSessionFilter</filter-name>
  <description>
      Close Hibernate session after each request
  </description>
  <filter-class>
      com.demo.HibernateSessionFilter
  </filter-class>
</filter>

<filter-mapping>
   <filter-name>HibernateSessionFilter</filter-name>
   <servlet-name>MyFrontControllerServlet</servlet-name>
</filter-mapping>


Listeners
ServletContextListener

• Its implementations receives notifications about changes to the servlet context of the web application.
• contextInitialized(ServletContextEvent sce)
• called when web application is ready to process requests
• contextDestroyed(ServletContextEvent sce)
• called when servlet context is about to be shut down

ServletContextAttributeListener

• Its implementation receives notifications of changes to the attribute list on the servlet context of a web application 
• attributeAdded(ServletContextAttributeEvent scab)
• called after a new attribute is added to the servlet context
• attributeRemoved(ServletContextAttributeEvent scab)
• called after an existing attribute has been removed from the servlet context
• attributeReplaced(ServletContextAttributeEvent scab)
• called after an attribute on the servlet context has been replaced

HttpSessionAttributeListener

• It can be used to get notifications of changes to the attribute lists of sessions within this web application.
• attributeAdded(ServletContextAttributeEvent scab)
• called after a new attribute was added to the servlet context.
• attributeRemoved(ServletContextAttributeEvent scab)
• called after an existing attribute has been removed from the servlet context.
• attributeReplaced(ServletContextAttributeEvent scab)
• called when an attribute on the servlet context has been replaced

HttpSessionListener

• notifies for the changes to the list of active sessions in a web application.
• sessionCreated(HttpSessionEvent se)
• called when a session is created
• sessionDestroyed(HttpSessionEvent se)
• called when a session is invalidated

HttpSessionActivationListener

• Objects that are bound to a session may listen to container events notifying them that sessions will be passivated and that session will be activated.
• It can be used when a container that migrates session between VMs or persists sessions and it is required to notify all attributes bound to sessions.

HttpSessionBindingListener 

• Object is notified when it is bound to or unbound from a session.

Example
<listener>
   <listener-class>
        com.francetelecom.csrtool.gui.init.StartupListener
   </listener-class>
</listener>


display-name

• Display name of web application

Example
<display-name>My App</display-name>


Icon

• small-icon
• large-icon

Example
<icon>
    <small-icon>/resource/icons/demoSmall.gif</small-icon>
    <large-icon>/resource/icons/demoBig.gif</large-icon>
</icon>




welcome-file-list

• Default file or URL pattern to redirect at entering context root

Example
<welcome-file-list>
   <welcome-file>index.jsp</welcome-file>
</welcome-file-list>