Servlet context parameters and ServletContext interface

Context parameters:

Context parameters refers to the initialization parameters for all servlets of an application. <context-param> attribute is used to define a context parameter. <context-param> attribute has two main sub attributes <param-name> and <param-value>. The <param-name> contains the name of the parameter and <param-value> contains the value of the parameter.

ServletContext interface:

ServletContext interface is used to access the context parameters.

Commonly used methods of ServletContext interface:

1. getInitParameter(String name): Returns the value of the specified parameter if parameter exist otherwise return null.
Syntax:

public String getInitParameter(String name)

2. getInitParameterNames(): Returns the names of context parameters as Enumeration if servlet has context parameters otherwise returns an empty Enumeration.
Syntax:

public Enumeration getInitParameterNames()

3. setAttribute(String name,Object object): Binds the specified object to the specified attribute name and put this attribute in application scope.
Syntax:

public void setAttribute(String name,Object object)

4. getAttribute(String name): Returns the specified attribute if exist otherwise returns null.
Syntax:

public Object getAttribute(String name)

5. removeAttribute(String name): Removes the specified attribute.
Syntax:

public void removeAttribute(String name)

Example:

ContextParamExample.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * This class is used to show the use of context parameters.
 * @author w3spoint
 */
public class ContextParamExample extends HttpServlet {
   private static final long serialVersionUID = 1L;
 
   //no-argument constructor.
    public ContextParamExample() {
 
    }
 
    protected void doGet(HttpServletRequest request, 
		HttpServletResponse response)
	              throws ServletException, IOException {
	response.setContentType("text/html"); 
    	PrintWriter out = response.getWriter();
    	//get ServletContext object.
    	ServletContext context=getServletContext();  
    	//get context parameter from ServletContext object.
    	String appUser = context.getInitParameter("appUser");
 
    	out.print("<h1>Application User: " + appUser + "</h1>");
 
    	out.close();
    }
 
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns="http://java.sun.com/xml/ns/javaee" 
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
id="WebApp_ID" version="2.5">
 
  <servlet>
    <servlet-name>ContextParamExample</servlet-name>
    <servlet-class>
    	com.w3spoint.business.ContextParamExample
    </servlet-class>
  </servlet>
 
  <context-param>
  	<param-name>appUser</param-name>  
	<param-value>jai</param-value>  
  </context-param>
 
  <servlet-mapping>
    <servlet-name>ContextParamExample</servlet-name>
    <url-pattern>/ContextParamExample</url-pattern>
  </servlet-mapping>
 
</web-app>

Output:

servlet example 8

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