ServletContext Object

1. ServletContext object is created by the servlet container
2. ServletContext object is contained within ServletConfig object
3. ServletContext object is used to get configuration information from web.xml file
4. There is one ServletContext object per application

Note -> If some information needs to be shared across all the servlets in the application, then it can be stored in ServletContext object.

ServletContext commonly used methods

Method	Description
public String getInitParameter(String name)	Gives the value of the passed parameter
public Enumeration getInitParameterNames()	Gives all the initialization parameters
public void setAttribute(String name,Object object)	Sets the value of an attribute
public Object getAttribute(String name)	Gets the value of the passed attribute
public void removeAttribute(String name)	Removes the passed attribute

How to define servlet context parameters in web.xml

Context parameters are defined in web.xml under the <web-app> element. Refer the below diagram. Here three context parameters are defined

How to get ServletContext object

ServletContext context = getServletContext();
or
ServletContext context = getServletConfig().getServletContext();

ServletContext Example

package com.sks;

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;

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

		//Getting ServletContext object
		ServletContext context = getServletContext();

		// Getting the value of the initialization parameter and printing it
		String contextParam1 = context.getInitParameter("contextParam1");
		writer.println("Context parameter contextParam1 is = " + contextParam1);

		writer.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"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="WebApp_ID" version="3.0">
	<display-name>my-first-servlet-app</display-name>
	
	<context-param>
		<param-name>contextParam1</param-name>
		<param-value>abc</param-value>
	</context-param>
	
	<context-param>
		<param-name>contextParam2</param-name>
		<param-value>pqr</param-value>
	</context-param>
	
	<context-param>
		<param-name>contextParam3</param-name>
		<param-value>xyz</param-value>
	</context-param>

	<servlet>
		<servlet-class>com.sks.ServletContextExample</servlet-class>
		<servlet-name>myServlet</servlet-name>
	</servlet>

	<servlet-mapping>
		<servlet-name>myServlet</servlet-name>
		<url-pattern>/my</url-pattern>
	</servlet-mapping>

</web-app>

Example to get all the parameters

package com.sks;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

		//Getting ServletContext object
		ServletContext context = getServletContext();

		Enumeration<String> contextParams = context.getInitParameterNames();  
	      
		String str = "";  
		writer.print("Printing the context initialization parameters : ");
		while(contextParams.hasMoreElements()){  
		    str = contextParams.nextElement();  
		    writer.print("<br> " + context.getInitParameter(str));  
		}  

		writer.close();
	}
}

Run the application and check the output