Web application and Servlets notes

Servlet Context and Session Listeners

• Servlet context listeners.
– These listeners are notified when the servlet context (i.e., the Web application) is initialized and destroyed.
• Servlet context attribute listeners.
– These listeners are notified when attributes are added to, removed from, or replaced in the servlet context.
• Session listeners.
– These listeners are notified when session objects are created, invalidated, or timed out.
• Session attribute listeners.
– These listeners are notified when attributes are added to, removed from, or replaced in any session.

Implement the appropriate interface.
– Use ServletContextListener, ServletContextAttributeListener,
HttpSessionListener, or HttpSessionAttributeListener

Use these objects.
– This process is application specific, but there are some common
themes. For example, with the servlet context, you are most likely
to read initialization parameters (getInitParameter), store data for
later access (setAttribute), and read previously stored data
(getAttribute).

Declare the listener.
– You do this with the listener and listener-class
elements of the general Web application deployment descriptor
(web.xml) or of a tag library descriptor file.

Provide any needed initialization parameters.
– Servlet context listeners commonly read context initialization
parameters to use as the basis of data that is made available to all
servlets and JSP pages. You use the context-param web.xml
element to provide the names and values of these initialization
parameters.

How to pass parameters to whole web application – ServletContext

Posted on December 2, 2009 ,     Last modified : August 30, 2012

By mkyong

Here’s a serlvet code example to demonstrate how to pass a parameter to whole web application by using ServletContext “init-param” in web.xml.

In the deployment descriptor (web.xml)

Put your parameter value in “init-param” and make sure outside the “servlet” element

        <servlet>
  <servlet-name>ServletName</servlet-name>
  <servlet-class>com.mkyong.ServletDemo</servlet-class>
 </servlet>
 
 <context-param>
   <param-name>email</param-name>
   <param-value>admin@email.com</param-value>
 </context-param>

Servlet code

public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws IOException{
 
  PrintWriter pw = response.getWriter();
  pw.println(getServletContext().getInitParameter("email"));
 
 }

The “getServletContext().getInitParameter(“email”)” method is use to get the ServletContext parameter value in web.xml. In addition , this parameter is accessible by the whole web application.

How to pass parameters to a servlet – ServletConfig

Posted on December 2, 2009 ,     Last modified : August 30, 2012

By mkyong

Here’s a serlvet code example to demonstrate how to pass a parameter to a servlet by using ServletConfig “init-param” in web.xml

In the deployment descriptor (web.xml)

Put your parameter value in “init-param” and make sure inside the “servlet” element

        <servlet>
  <servlet-name>ServletName</servlet-name>
  <servlet-class>com.mkyong.ServletDemo</servlet-class>
 
  <init-param>
   <param-name>email</param-name>
   <param-value>admin@email.com</param-value>
  </init-param>
 </servlet>
 
 <servlet-mapping>
  <servlet-name>ServletName</servlet-name>
  <url-pattern>/Demo</url-pattern>
 </servlet-mapping>

Servlet code

public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws IOException{
 
  PrintWriter pw = response.getWriter();
  pw.println(getServletConfig().getInitParameter("email"));
 
 }

The “getServletConfig().getInitParameter(“email”)” method is use to get the ServletConfig parameter value in web.xml. Btw, this parameter only available for this servlet only. If you want a parameter which allow globally access by whole web application, you need put the parameter in servlet context element.
Here’s an example to pass parameter to whole web application.