import javax.servlet.ServletRequestAttributeEvent; import javax.servlet.ServletRequestAttributeListener; import javax.servlet.annotation.WebListener; 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 javax.servlet.*; import javax.servlet.annotation.WebListener; @WebListener public class ContextListener1 implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) { ServletContext context = sce.getServletContext(); /* Add Context Listener */ System.out.println("Adding ReqAttrListener"); context.addListener(ReqAttrListener.class); System.out.println("ContextListener1 Initialized"); } @Override public void contextDestroyed(ServletContextEvent sce) { System.out.println("Context Listener1 Destroyed"); } }
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"); } } }
Run
' SampleApp', server console has messages like below.
Info: Adding ReqAttrListener Info: ContextListener1 Initialized Info: Loading application [servlet] at [/servlet] Info: servlet was successfully deployed in 322 milliseconds. Info: name Added Info: name Replaced Info: name Removed
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