ServletContextAttributeListener监听器实战

- 日理万妓 2021-07-24 16:25 328阅读 0赞

**一 代码**

package lee;
    
    import javax.servlet.*;
    import javax.servlet.annotation.*;
    
    @WebListener
    public class MyServletContextAttributeListener
        implements ServletContextAttributeListener
    {
        // 当程序向application范围添加属性时触发该方法
        public void attributeAdded(ServletContextAttributeEvent event)
        {
            ServletContext application = event.getServletContext();
            // 获取添加的属性名和属性值
            String name = event.getName();
            Object value = event.getValue();
            System.out.println(application + "范围内添加了名为"
                + name + "，值为" + value + "的属性!");
        }
        // 当程序从application范围删除属性时触发该方法
        public void attributeRemoved(ServletContextAttributeEvent event)
        {
            ServletContext application = event.getServletContext();
            // 获取被删除的属性名和属性值
            String name = event.getName();
            Object value = event.getValue();
            System.out.println(application + "范围内名为"
                + name + "，值为" + value + "的属性被删除了!");
        }
        // 当application范围的属性被替换时触发该方法
        public void attributeReplaced(ServletContextAttributeEvent event)
        {
            ServletContext application = event.getServletContext();
            // 获取被替换的属性名和属性值
            String name = event.getName();
            Object value = event.getValue();
            System.out.println(application + "范围内名为"
                + name + "，值为" + value + "的属性被替换了!");
        }
    }

**二 测试JSP**

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
    <%@ page import="java.sql.*" %>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <title> 测试ServletContextListener </title>
        <meta name="website" content="http://www.crazyit.org" />
    </head>
    <body>
    下面是直接从application中取出数据库连接，<br/>
    并执行查询后的结果<br/>
    <%
    Connection conn = (Connection)application.getAttribute("conn");
    // 创建Statement对象
    Statement stmt = conn.createStatement();
    // 执行查询
    ResultSet rs = stmt.executeQuery("select * from news_inf");
    %>
    <table bgcolor="#9999dd" border="1" width="300">
    <%
    // 遍历结果集
    while(rs.next())
    {
    %>
    <tr>
    <td><%=rs.getString(1)%></td>
    <td><%=rs.getString(2)%></td>
    </tr>
    <%
    }
    %>
    <table>
    </body>
    </html>

**三 测试**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

日志文件输出

org.apache.catalina.connector.RequestFacade@2b5e78d5范围内名为org.apache.catalina.ASYNC_SUPPORTED，值为true的属性被替换了!

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/421aa0d3327f4815bb89bb354b0a6e75.png