Servlet Context theoretical doubt : HF book

[Rahul Sudip Bose]

I am unable to understand what exactly is servlet context used for ? Can you suggest examples from real-world applications ?
The HF book says "Its a kind of application bulletin-board, where you can put up messages (called attributes) that other parts of the application can access" . Can anyone suggest an example that demonstrates this ? And why would i want to "put up messages (called attributes) that other parts of the application can access" ?

There is a servlet that allows a user to download a jar file. How does it fit into the above explanation ?

here is a part of that servlet code :

//some code here
response.setContentType("application/jar");

ServletContext ctx = getServletContext();
InputStream is = ctx.getResourceAsStream("/bookcode.jar");
//some code here

PS : please be frank and let me know if this is a silly doubt.

[Mike Zal]

My favorite example of this is a "Contact Us" email address. Suppose the email address is 'contact at domain.org' . It would be a horrible practice to hard hard the email address value into a JSP. If at some future point the address needs to change, you would need to change the hard coded value in every JSP.

Imagine that the following code runs on application start up

getServletContext().setAttribute("contactAttribute","contact at domain dot org");

This saves the String "contact at domain dot org" to a variable that any part of the application can use. Now instead of hard coding 'contact at domain.org' you can do either of the following
Inside a Servlet

String contact = (String)getServletContext().getAttribute("contactAttribute");
out.print("Email us at: "+contact);

Inside a JSP with Scriptlets

Email us at: <%= application.getAttribute(contactAttribute) %>

Inside a JSP with EL

Email us at: ${applicationScope.contactAttribute}

[Nabila Mohammad]

Great Explanation!