Session監聽器

Session 內置對象的監聽器

Demo: 監聽 session 的狀態
1.定義 session 內置對象的狀態監聽器

 1 public class SessionListener implements HttpSessionListener {  2  @Override  3     public void sessionCreated(HttpSessionEvent event) {  4         System.out.println("建立 session 內置對象:" + event.getSession().getId());  5  }  6  @Override  7     public void sessionDestroyed(HttpSessionEvent event) {  8         System.out.println("銷燬了 session 內置對象:" + event.getSession().getId());  9  } 10 }

2.配置 session 內置對象的狀態監聽器

<listener>
      <listener-class>com.sxt.mvcpro.listener.SessionListener</listener-class>
  </listener>

3.獲取 session 內置對象

1 @SuppressWarnings("serial") 2 public class EmpServlet extends HttpServlet{ 3  @Override 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 5  req.getSession(); 6         System.out.println("訪問了 servlet 方法"); 7  } 8 }

4.銷燬 session 內置對象

1 @SuppressWarnings("serial") 2 public class EmpServlet extends HttpServlet{ 3  @Override 4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { 5  req.getSession().invalidate(); 6  } 7 }

Demo: 監聽 session 的屬性
1.定義 session 內置對象的屬性監聽器

 1 1.定義 session 內置對象的屬性監聽器  2 public class SessionAttributeListener implements HttpSessionAttributeListener {  3  @Override  4     public void attributeAdded(HttpSessionBindingEvent event) {  5         System.out.println("增長屬性時候觸發: " + event.getName() + ":" + event.getValue());  6  }  7  @Override  8     public void attributeRemoved(HttpSessionBindingEvent event) {  9         System.out.println("刪除屬性時候觸發: " + event.getName() + ":" + event.getValue()); 10  } 11  @Override 12     public void attributeReplaced(HttpSessionBindingEvent event) { 13         System.out.println("替換屬性時候觸發: " + event.getName() + ":" + event.getValue()); 14  } 15 }

2.配置 session 內置對象的屬性監聽器

1   <listener>
2       <listener-class>com.sxt.mvcpro.listener.SessionAttributeListener</listener-class>
3   </listener>

3.測試監聽器

 1 @SuppressWarnings("serial")  2 public class EmpServlet extends HttpServlet{  3  @Override  4     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  5         HttpSession session = req.getSession();  6         //增長屬性
 7         session.setAttribute("name", "李四");  8         //替換屬性
 9         session.setAttribute("name", "張三"); 10         //刪除屬性
11         session.removeAttribute("name"); 12  } 13 }

Demo: 訪問 jsp 頁面的時候爲何會觸發 sessionCreated 方法?
　　訪問 jsp 頁面的時候容器會將 jsp 頁面轉換成一個特殊的 Servlet,
　　先將其轉換爲對應的*.java 源碼(源碼會調用sessionCreated ), 以後再將源碼編譯成對應的*.class,
　　以後發那會給瀏覽器以前會被解析爲 html 代碼給到瀏覽器解析時