ServletContext Example context-param

Before going ServletContext Example, see the difference between <init-param> and <context-param>, both written in web.xml file.

What is <init-param>?

 
  portnumber 
  8888 

We have seen the above code in Servlet web xml init param Example using ServletConfig where the "portnumber" and "8888" are accessible for the particular servlet "ReadInitParamValues". Other servlets in the container cannot access this data. That is, the <init-param> is accessible to one servlet only or it can be said the <init-param> data is private for a particular servlet.

What is <context-param>?

Now is there anyway, the data of <init-param> is accessible to all the servlets under execution in the container? Yes, there exists; we write the <init-param> outside of any <servlet> tag in the same web.xml file. For this, <context-param> (instead of <init-param>) is used as follows.

  goldrate
  3100.5

Because the tag <context-param> exists, in the web.xml, outside any servlet tag (say, global area), every servlet can access it.

Finally, <init-param> data is local for a particular servlet and context-param data is global for all servlets. This is the difference between <init-param> and <context-param>.

Following ServletContext Example illustrates

The aim of this program is the servlet reads the weight of gold article from the client HTML file and the gold rate from <context-param> and estimates the bill amount payable.

Client Program: ClientData.html

   

     Enter Gold Weight 
     
   

web.xml entry for the Servlet

  Welcome to Tomcat
  
     Welcome to Tomcat
  

  
    goldrate
    3100.5
  

  
    klm
    ContextReading
  

  
    klm
    /conread
  

Servlet Program: ContextReading.java

import javax.servlet.*; 
import javax.servlet.http.*;
import java.io.*; 

public class ContextReading extends HttpServlet
{
  public void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
  {
    res.setContentType("text/html");
    PrintWriter out = res.getWriter();

                                      // reading gold weight from client file, ClientData.html
    String gold = req.getParameter("t1");
    int gw = Integer.parseInt(gold);

                                      // reading gold rate from  of web.xml file
    ServletContext sc1 = getServletContext();
    String rate = sc1.getInitParameter("goldrate");
    double gr = Double.parseDouble(rate);

                                      // estimate and make bill
    double total = gw * gr;
    out.println("Your Gold Purchase Information:
");
    out.println("Gold Weight: " + gw + " gms.
");
    out.println("Gold Rate Rs." + gr + "/gm.
");
    out.println("To pay Rs." + total);

    out.close();
  }
}

Following is the client Screen: ClientData.html

Output screen when submit is clicked after entering gold weight.

Screenshot of ServletContext Example