Dinesh on Java

An object of ServletContext is created by the web container at time of deploying the project. This object can be used to get configuration information from web.xml file. There is only one ServletContext object per web application.If any information is shared to many servlet, it is better to provide it from the web.xml file using the element.

Advantage of ServletContext

Easy to maintain if any information is shared to all the servlet, it is better to make it available for all the servlet. We provide this information from the web.xml file, so if the information is changed, we don’t need to modify the servlet. Thus it removes maintenance problem.

Usage of ServletContext Interface

There can be a lot of usage of ServletContext object. Some of them are as follows:

• The object of ServletContext provides an interface between the container and servlet.
• The ServletContext object can be used to get configuration information from the web.xml file.
• The ServletContext object can be used to set, get or remove attribute from the web.xml file.
• The ServletContext object can be used to provide inter-application communication.

Methods	Description
Object getAttribute(String name)	returns the container attribute with the given name, or null if there is no attribute by that name.
String getInitParameter(String name)	returns parameter value for the specified parameter name, or null if the parameter does not exist
Enumeration getInitParameterNames()	returns the names of the context’s initialization parameters as an Enumeration of String objects
void setAttribute(String name,Object obj)	set an object with the given attribute name in the application scope
void removeAttribute(String name)	removes the attribute with the specified name from the application context

How to get the object of ServletContext

ServletContext app = getServletContext();
ServletContext app = getServletConfig().getServletContext(); 

 

How to get the object of ServletContext interface

getServletContext() method of ServletConfig interface returns the object of ServletContext.
    getServletContext() method of GenericServlet class returns the object of ServletContext.

Syntax of getServletContext() method

public ServletContext getServletContext()  

Example of getServletContext() method

//We can get the ServletContext object from ServletConfig object  
    ServletContext application=getServletConfig().getServletContext();  
      
    //Another convenient way to get the ServletContext object  
    ServletContext application=getServletContext();  

Example of ServletContext to get the initialization parameter

In this example, we are getting the initialization parameter from the web.xml file and printing the value of the initialization parameter. Notice that the object of ServletContext represents the application scope. So if we change the value of the parameter from the web.xml file, all the servlet classes will get the changed value. So we don’t need to modify the servlet. So it is better to have the common information for most of the servlets in the web.xml file by context-param element. Let’s see the simple example:
HelloServlet.java

import java.io.*;  
    import javax.servlet.*;  
    import javax.servlet.http.*;  
      
      
    public class HelloServlet extends HttpServlet{  
    public void doGet(HttpServletRequest req,HttpServletResponse res)  
    throws ServletException,IOException  
    {  
    res.setContentType("text/html");  
    PrintWriter pw=res.getWriter();  
      
    //creating ServletContext object  
    ServletContext context=getServletContext();  
      
    //Getting the value of the initialization parameter and printing it  
    String driverName=context.getInitParameter("driverName");  
    pw.println("driver name is="+driverName);  
      
    pw.close();  
      
    }
}  

web.xml

<web-app>  
      
    <servlet>  
    <servlet-name>HelloServlet</servlet-name>  
    <servlet-class>HelloServlet</servlet-class>  
    </servlet>  
      
    <context-param>  
    <param-name>driverName</param-name>  
    <param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value>  
    </context-param>  
      
    <servlet-mapping>  
    <servlet-name>HelloServlet</servlet-name>  
    <url-pattern>/context</url-pattern>  
    </servlet-mapping>  
      
    </web-app> 

Example of ServletContext to get all the initialization parameters

In this example, we are getting all the initialization parameter from the web.xml file. For getting all the parameters, we have used the getInitParameterNames() method in the servlet class.

HelloServlet.java

import java.io.*;  
import javax.servlet.*;  
import javax.servlet.http.*;  
  
  
public class DemoServlet extends HttpServlet{  
public void doGet(HttpServletRequest req,HttpServletResponse res)  
throws ServletException,IOException  
{  
res.setContentType("text/html");  
PrintWriter out=res.getWriter();  
  
ServletContext context=getServletContext();  
Enumeration<string> e=context.getInitParameterNames();  
      
String str="";  
while(e.hasMoreElements()){  
    str=e.nextElement();  
    out.print("<br> "+context.getInitParameter(str));  
}  
}
}  

web.xml

<web-app>  
      
    <servlet>  
    <servlet-name>HelloServlet</servlet-name>  
    <servlet-class>HelloServlet</servlet-class>  
    </servlet>  
      
    <context-param>  
    <param-name>driverName</param-name>  
    <param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value>  
    </context-param>  
      
    <context-param>  
    <param-name>name</param-name>  
    <param-value>dinesh</param-value>  
    </context-param>  
      
    <context-param>  
    <param-name>email</param-name>  
    <param-value>admin@dineshonjava.com</param-value>  
    </context-param>  
      
    <servlet-mapping>  
    <servlet-name>HelloServlet</servlet-name>  
    <url-pattern>/context</url-pattern>  
    </servlet-mapping>  
      
    </web-app>