Use of Java Web Listener (1) Listening for context and session information, Java Web Listener

Use of Java Web Listener (1) Listening for context and session information, Java Web Listener

1. Listener context class

1 package com. examp. ch9; 2 3 import java. io. fileOutputStream; 4 import java. io. printWriter; 5 import java. util. date; 6 7 import javax. servlet. servletContext; 8 import javax. servlet. servletContextAttributeEvent; 9 import javax. servlet. servletContextAttributeListener; 10 import javax. servlet. servletContextEvent; 11 import javax. servlet. servletContextListener; 12 13 public final class implements ServletContextListener, listener {16 private ServletContext context = null; 17 18 public void contextDestroyed (ServletContextEvent sce) 19 {20 logout ("Call contextDestroyed () method --> ServletContext is destroyed "); 21 this. context = null; 22} 23 24 public void contextInitialized (ServletContextEvent sce) 25 {26 this. context = sce. getServletContext (); 27 logout ("Call the contextInitialized () method --> ServletContext initialization"); 28} 29 30 public void attributeAdded (ServletContextAttributeEvent scae) 31 {32 logout ("Call attributeAdded ('" + scae. getName () + "','" + scae. getValue () + 33 "') Method --> added an attribute"); 34} 35 36 public void attributeRemoved (ServletContextAttributeEvent scae) 37 {38 logout ("attributeRemoved ('" + scae. getName () + "','" + scae. getValue () + 39 "') Method --> Delete this attribute"); 40} 41 42 public void attributeReplaced (ServletContextAttributeEvent scae) 43 {44 logout ("attributeReplaced ('" + scae. getName () + "','" + scae. getValue () + 45 "') Method --> changed this attribute"); 46} 47 48 private void logout (String message) 49 {50 PrintWriter out = null; 51 try52 {53 out = new PrintWriter (new FileOutputStream ("E :\\ contextLog.txt", true); 54 out. println (new Date (). toLocaleString () + message); 55 out. close (); 56} 57 catch (Exception e) 58 {59 out. close (); 60 e. printStackTrace (); 61} 62} 63}

2. Classes for listening to Http sessions

1 package com. examp. ch9; 2 3 import java. io. fileOutputStream; 4 import java. io. printWriter; 5 import java. util. date; 6 7 import javax. servlet. servletContext; 8 import javax. servlet. servletContextEvent; 9 import javax. servlet. http. httpSessionAttributeListener; 10 import javax. servlet. http. httpSessionBindingEvent; 11 import javax. servlet. http. httpSessionEvent; 12 import javax. servlet. http. httpSessionListener; 13/* 14 * HttpSessionListener Http session creation and destruction 15 * Http sessionattributelistener listens for changes in session attributes 16 */17 public final class MySessionListener implements listener, HttpSessionListener18 {19 ServletContext context; // create a context object 20 int users = 1; // The number of initial users is 121/* 22 * this operation is triggered when an object is added to the session. In general, this operation is triggered by calling the setAttribute Method 23*24 */25 public void. attributeAdded (HttpSessionBindingEvent event) 26 {27 logout ("attributeAdded ('" + event. getSession (). getId () + "','" + 28 event. getName () + "','" + event. getValue () + "')"); 29} 30/* 31 * this operation is triggered when you modify or delete an object added to a session. In general, the 32*33 */34 public void attributeRemoved (httpSessionBindingEvent event) 35 {36 logout ("attributeRemoved ('" + event. getSession (). getId () + "','" + 37 event. getName () + "','" + event. getValue () + "')"); 38} 39/* 40 * when the Session attribute is reset 41*42 */43 public void attributeReplaced (HttpSessionBindingEvent se) 44 {45 logout ("attributeReplaced ('" + se. getSession (). getId () + ", '" + se. getName () + "','" + se. getValue () + "')"); 46} 47 48 49 50/* 51 * triggering when creating a session is also the first time that the client triggers 52 */53 public void sessionCreated (HttpSessionEvent event) when interacting with the server) 54 {55 System. out. println (users); 56 this. users + = 1; // get the ID and number of users 57 logout ("sessionCreated ('" + event. getSession (). getId () + "'), currently" + this. users + "users"); 58 this. context. setAttribute ("users", new Integer (this. users )); // saves the number of users to context59} 60/* 61 * to destroy the session. Generally, only one button is triggered to destroy the session, or 62*63 */64 public void sessionDestroyed (HttpSessionEvent event) is scheduled to be destroyed) 65 {66 this. users --; 67 logout ("sessionDestroyed ('" + event. getSession (). getId () + "'), currently" + this. users + "users"); // obtain the ID and number of users 68 this. context. setAttribute ("users", new Integer (this. users); // saves the number of users to context69} 70 71 public void contextDestroyed (ServletContextEvent sce) 72 {73 logout ("contextDestroyed () --> ServletContext is destroyed "); 74 this. context = null; 75} 76 77 public void contextInitialized (ServletContextEvent sce) 78 {79 this. context = sce. getServletContext (); 80 logout ("contextInitialized () --> ServletContext initialized"); 81} 82 83 private void logout (String message) 84 {85 PrintWriter out = null; 86 try87 {// create input stream Write File 88 out = new PrintWriter (new FileOutputStream ("E: \ sessionLog.txt", true); 89 out. println (new Date (). toLocaleString () + "-->" + message); 90 out. close (); 91} 92 catch (Exception e) 93 {94 out. close (); 95 e. printStackTrace (); 96} 97} 98}

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3. Front-end JSP file

Context_test.jsp

1 <%@ page contentType="text/html;charset=UTF-8"%>2 <%3 out.println("add attribute");4 getServletContext().setAttribute("userName","Smith");5 out.println("replace attribute");6 getServletContext().setAttribute("userName","Kate");7 out.println("remove attribute");8 getServletContext().removeAttribute("userName");9 %>

Session_test.jsp

1 <% @ page contentType = "text/html; charset = UTF-8" %> 2: 3 session. setAttribute ("userName", "Smith") <br> 4 <% session. setAttribute ("userName", "Smith"); %> <! -- Add Property --> 5 session. setAttribute ("userName", "Kate") <br> 6 <% session. setAttribute ("userName", "Kate"); %> <! -- Change attributes --> 7 session. removeAttribute ("userName", "Kate") <br> 8 <% session. removeAttribute ("userName"); %> <! -- Delete attribute --> 9 currently has <% = getServletContext (). getAttribute ("users") %> users. <Br> 10 after session. invalidate () <br> 11 <% session. invalidate (); %> <! -- Destroy this session --> 12 currently has <% = getServletContext (). getAttribute ("users") %> users.