Context parameters:
Context parameters refer 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:
The 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 the parameter exists otherwise returns null.
Syntax:
public String getInitParameter(String name)
2. getInitParameterNames(): Returns the names of context parameters as Enumeration if the 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 puts this attribute in the application scope.
Syntax:
public void setAttribute(String name,Object object)
4. getAttribute(String name): Returns the specified attribute if exists 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 W3schools360 */ 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("Application User: " + appUser + ""); 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.w3schools.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>