## 監聽三個對象的屬性的變化 添加,替換,刪除. ### ServletContextAttributeListener web.xml ~~~ <listener> <listener-class>com.like.attr.MyServletContextAttrListener</listener-class> </listener> ~~~ ~~~ public class MyServletContextAttrListener implements ServletContextAttributeListener { @Override public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) { System.out.println("ServletContext屬性添加了 :" + servletContextAttributeEvent.getName() + "," + servletContextAttributeEvent.getValue()); } @Override public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) { System.out.println("ServletContext屬性移除了 :" + servletContextAttributeEvent.getName() + "," + servletContextAttributeEvent.getValue()); } @Override public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) { System.out.println("ServletContext屬性替換了 :" + servletContextAttributeEvent.getName() + "," + servletContextAttributeEvent.getValue()); } } ~~~ 創建add.jsp ~~~ <% application.setAttribute("name", "jack"); %> ~~~ 創建update.jsp ~~~ <% application.setAttribute("name", "milan"); %> ~~~ 創建remove.jsp ~~~ <% application.removeAttribute("name"); %> ~~~ 訪問三個頁面觸發不同監聽器方法. 注意:第一次添加的時候會執行三次. ``` ServletContext屬性添加了 :org.apache.jasper.runtime.JspApplicationContextImpl,org.apache.jasper.runtime.JspApplicationContextImpl@521dec7e ServletContext屬性添加了 :org.apache.jasper.compiler.ELInterpreter,org.apache.jasper.compiler.ELInterpreterFactory$DefaultELInterpreter@66ce0f61 ServletContext屬性添加了 :name,jack //顯示的是添加的值 ServletContext屬性替換了 :name,jack //顯示的是被替換的值 ServletContext屬性移除了 :name,milan //顯示的是被移除的值 ``` ### ServletRequestAttributeListener 同上 ### ServletSessionAttributeListener 同上