監聽器使用 · Servlet

[TOC] # 1. 監聽Context對象的創建和銷毀步驟如下： **1. 實現接口ServletContextListener** ```java public class CustomServletContextListener implements ServletContextListener { @Override public void contextInitialized(ServletContextEvent sce) { //可以獲取ServletContext -> sce.getServletContext() System.out.println(this.getClass().getSimpleName() + "->應用啟動了"); } @Override public void contextDestroyed(ServletContextEvent sce) { System.out.println(this.getClass().getSimpleName() + "->應用關閉了"); } } ``` **2. `web.xml`中啟用監聽器** ```xml <listener> <listener-class>com.learn.servlet02.listener.CustomServletContextListener</listener-class> </listener> ``` **3. 演示** 啟動項目，然后再關閉項目，控制打印結果如下。 ```java CustomServletContextListener->應用啟動了 CustomServletContextListener->應用關閉了 ``` <br/> # 2. 監聽Request對象屬性的變化步驟如下： **1. 編寫一個Servlet類方便用來演示** ```java @WebServlet("/listener") public class ListenerServlet extends BaseServlet { public void listener01(HttpServletRequest request, HttpServletResponse response) { //添加屬性 request.setAttribute("username", "zhangsan"); //替換屬性 request.setAttribute("username", "lisi"); //移除屬性 request.removeAttribute("username"); } } ``` **2. 實現接口ServletRequestAttributeListener** ```java public class CustomServletRequestAttributeListener implements ServletRequestAttributeListener { @Override public void attributeAdded(ServletRequestAttributeEvent srae) { //可以獲取ServletContext -> srae.getServletContext() //可以獲取ServletRequest -> srae.getServletRequest() System.out.println(this.getClass().getSimpleName() + "->添加屬性了"); System.out.println(srae.getServletRequest().getAttribute("username")); } @Override public void attributeRemoved(ServletRequestAttributeEvent srae) { System.out.println(this.getClass().getSimpleName() + "->移除屬性了"); System.out.println(srae.getServletRequest().getAttribute("username")); } @Override public void attributeReplaced(ServletRequestAttributeEvent srae) { System.out.println(this.getClass().getSimpleName() + "->替換屬性了"); System.out.println(srae.getServletRequest().getAttribute("username")); } } ``` **3. `web.xml`中啟用監聽器** ```xml <listener> <listener-class>com.learn.servlet02.listener.CustomServletRequestAttributeListener</listener-class> </listener> ``` **4. 訪問Servlet，控制臺打印結果如下** ``` CustomServletRequestAttributeListener->添加屬性了 zhangsan CustomServletRequestAttributeListener->替換屬性了 lisi CustomServletRequestAttributeListener->移除屬性了 null ``` <br/> # 3. 監聽實體類是否在session中步驟如下： **1. 編寫一個Servlet方便用來演示** ```java @WebServlet("/listener") public class ListenerServlet extends BaseServlet { public void listener03(HttpServletRequest request, HttpServletResponse response) { HttpSession session = request.getSession(); //將Student添加到session中 session.setAttribute("student", Student.builder().id(1).name("zhangsan").age(25).build()); //session.removeAttribute("student"); } } ``` **2. 實體類實現接口** ```java @Data @Builder public class Student implements HttpSessionBindingListener { private Integer id; private String name; private Integer age; /** * 當Student被session.setAttribute("student", Student)時該方法被調用. */ @Override public void valueBound(HttpSessionBindingEvent event) { //可以獲取HttpSession -> event.getSession() System.out.println(this.getClass().getSimpleName() + "->被添加到session了"); System.out.println(event.getSession().getAttribute("student")); } /** * Student是否被session.removeAttribute("student")時該方法都會被調用. */ @Override public void valueUnbound(HttpSessionBindingEvent event) { System.out.println(this.getClass().getSimpleName() + "->從session中移除了"); System.out.println(event.getSession().getAttribute("student")); } } ``` **3. 訪問Servlet，控制臺打印結果如下** ``` ---- 1. 當不調用session.removeAttribute("student")時控制臺打印如下 ---- Student->被添加到session了 Student(id=1, name=zhangsan, age=25) Student->從session中移除了 Student(id=1, name=zhangsan, age=25) ---- 2. 當調用session.removeAttribute("student")時控制臺打印結果如下 ---- Student->被添加到session了 null Student->從session中移除了 null ``` <br/> # 4. 監聽實體類序列化與反序列化步驟如下： **1. 實體類實現接口HttpSessionActivationListener, Serializable** ```java @Data @Builder public class Account implements HttpSessionActivationListener, Serializable { private Integer id; private String username; private String password; /** * Account隨session序列化時被調用 */ @Override public void sessionWillPassivate(HttpSessionEvent se) { System.out.println(this.getClass().getSimpleName() + "->序列化了"); System.out.println(se.getSession().getAttribute("account")); } /** * Account隨session反序列化時被調用 */ @Override public void sessionDidActivate(HttpSessionEvent se) { System.out.println(this.getClass().getSimpleName() + "->反序列化了"); System.out.println(se.getSession().getAttribute("account")); } } ``` **2. 編寫Servlet方便用來演示** ```java @WebServlet("/listener") public class ListenerServlet extends BaseServlet { public void listener02(HttpServletRequest request, HttpServletResponse response) { HttpSession session = request.getSession(); //將Account添加到session中 session.setAttribute("account", Account.builder().id(1).username("zhangsan").password("123456").build()); } } ``` **3. 編寫`webapp/META-INF/content.xml`方便用來演示** ```xml <Context>  <Manager className="org.apache.catalina.session.PersistentManager" maxIdleSwap="1"> <Store className="org.apache.catalina.session.FileStore" directory="gacl"/> </Manager> </Context> ``` **4. 訪問Servlet，然后等待1分鐘，再訪問Servlet，控制打印結果如下** ``` Account->序列化了 Account(id=1, username=zhangsan, password=123456) Account->反序列化了 Account(id=1, username=zhangsan, password=123456) ```