import javax.servlet.ServletRequestAttributeEvent; import javax.servlet.ServletRequestAttributeListener; public class ReqAttrListener implements ServletRequestAttributeListener { @Override public void attributeAdded(ServletRequestAttributeEvent e) { System.out.println(e.getName() +" Added"); } @Override public void attributeRemoved(ServletRequestAttributeEvent e) { System.out.println(e.getName() +" Removed"); } @Override public void attributeReplaced(ServletRequestAttributeEvent e) { System.out.println(e.getName() +" Replaced"); } }
import java.io.IOException; import java.io.PrintWriter; import javax.servlet.annotation.WebServlet; import javax.servlet.http.*; @WebServlet(urlPatterns = {"/SampleApp"}) public class SampleApp extends HttpServlet { @Override public void doGet(HttpServletRequest req, HttpServletResponse res)throws IOException{ try(PrintWriter out = res.getWriter()){ req.setAttribute("name", "Krishna"); req.setAttribute("name", "Arjun"); req.removeAttribute("name"); } } }
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.1" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"> <listener> <description>RequestAttributeListener</description> <listener-class>ReqAttrListener</listener-class> </listener> </web-app>
Run
' SampleApp', server console has messages like below.
Info: name Added Info: name Replaced Info: name Removed
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