如果要在部署Web應(yīng)用程序時(shí)執(zhí)行某些操作，例如創(chuàng)建數(shù)據(jù)庫連接，創(chuàng)建項(xiàng)目的所有表等，則需要實(shí)現(xiàn)ServletContextListener接口并提供其方法的實(shí)現(xiàn)。

ServletContextEvent類的構(gòu)造方法

在ServletContextEvent類中只定義了一個(gè)構(gòu)造函數(shù)。Web容器在ServletContext實(shí)例之后創(chuàng)建ServletContextEvent的實(shí)例。

ServletContextEvent(ServletContext e)

ServletContextEvent類的方法

ServletContextEvent類中只定義了一個(gè)方法：

public ServletContext getServletContext() - 返回ServletContext的實(shí)例。

ServletContextListener接口的方法

在ServletContextListener接口中聲明了兩種方法，這些方法必須由servlet程序員實(shí)現(xiàn)，以執(zhí)行一些操作，如創(chuàng)建數(shù)據(jù)庫連接等。

public void contextInitialized(ServletContextEvent e): 當(dāng)應(yīng)用程序部署在服務(wù)器上時(shí)被調(diào)用。
public void contextDestroyed(ServletContextEvent e): 當(dāng)應(yīng)用程序從服務(wù)器取消部署時(shí)被調(diào)用。

ServletContextEvent和ServletContextListener的示例

在這個(gè)例子中，從employees表中檢索數(shù)據(jù)。為了實(shí)現(xiàn)這個(gè)服務(wù)，我們在監(jiān)聽器類中創(chuàng)建了連接數(shù)據(jù)庫對(duì)象，并在servlet中使用了連接對(duì)象。

首先，在MySQL中創(chuàng)建一個(gè)名稱為：testdb 的數(shù)據(jù)庫，創(chuàng)建以下表及以數(shù)據(jù)記錄 -

DROP TABLE IF EXISTS `employees`;
CREATE TABLE `employees` (
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(64) NOT NULL DEFAULT '',
  `age` int(3) unsigned NOT NULL DEFAULT '0',
  `address` varchar(254) DEFAULT NULL,
  `salary` float(8,2) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=4 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of employees
-- ----------------------------
INSERT INTO `employees` VALUES ('1', '李小春', '23', '?？谑腥嗣翊蟮?800號(hào)', '8900.00');
INSERT INTO `employees` VALUES ('2', '張輝', '28', '廣州天河區(qū)珠村市場', '15800.00');
INSERT INTO `employees` VALUES ('3', '林賢弟', '25', '廣州白云區(qū)龍?zhí)链?20號(hào)', '18990.00');

打開Eclipse，創(chuàng)建一個(gè)動(dòng)態(tài)Web項(xiàng)目：ServletContextEvent，其完整的目錄結(jié)構(gòu)如下 -

以下是項(xiàng)目中的幾個(gè)主要的文件代碼。

文件：index.html -

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>ServletContextListener實(shí)例</title>
</head>
<body style="text-algin: center;">
    <a href="getdata">點(diǎn)擊讀取employees表中的數(shù)據(jù)</a>
</body>
</html>

文件：MyListener.java -

package com.yiibai;

import java.sql.Connection;
import java.sql.DriverManager;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * Application Lifecycle Listener implementation class MyListener
 *
 */
@WebListener
public class MyListener implements ServletContextListener {

    public void contextInitialized(ServletContextEvent event) {

        String jdbcDriver = "com.mysql.jdbc.Driver";
        String dbURL = "jdbc:mysql://localhost/testdb";

        // Database credentials
        String dbUser = "root";
        final String passwd = "123456";
        try {
            Class.forName(jdbcDriver);
            Connection con = DriverManager.getConnection(dbURL, dbUser, passwd);
            // storing connection object as an attribute in ServletContext
            ServletContext ctx = event.getServletContext();
            ctx.setAttribute("mycon", con);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void contextDestroyed(ServletContextEvent arg0) {
        System.out.println("Servlet has contextDestroyed...");
    }

}

文件：FetchData.java -

package com.yiibai;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class FetchData
 */
public class FetchData extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();

        try {
            // Retrieving connection object from ServletContext object
            ServletContext ctx = getServletContext();
            Connection con = (Connection) ctx.getAttribute("mycon");
            if(con==null) {
                System.out.println("獲取數(shù)據(jù)庫連接異常~！");
            }
            // retieving data from emp32 table
            String sql = "SELECT * FROM employees";
            PreparedStatement ps = con.prepareStatement(sql, ResultSet.TYPE_SCROLL_SENSITIVE,
                    ResultSet.CONCUR_UPDATABLE);

            ResultSet rs = ps.executeQuery();
            while (rs.next()) {
                out.print("<br>" + rs.getString(1) + " " + rs.getString(2));
            }
            con.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

        out.close();
    }
}

文件：web.xml -

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
    id="WebApp_ID" version="3.1">
    <display-name>ServletContextEvent</display-name>
    <welcome-file-list>
        <welcome-file>index.html</welcome-file>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <listener>
        <listener-class>com.yiibai.MyListener</listener-class>
    </listener>
    <servlet>
        <servlet-name>FetchDataServlet</servlet-name>
        <servlet-class>com.yiibai.FetchData</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>FetchDataServlet</servlet-name>
        <url-pattern>/getdata</url-pattern>
    </servlet-mapping>
</web-app>

在編寫上面代碼后，部署此Web應(yīng)用程序(在項(xiàng)目名稱上點(diǎn)擊右鍵->”Run On Server…”)，打開瀏覽器訪問URL： http://localhost:8080/ServletContextEvent/ ，如果沒有錯(cuò)誤，應(yīng)該會(huì)看到以下結(jié)果 -

點(diǎn)擊上面鏈接后，從數(shù)據(jù)庫表中讀取到的數(shù)據(jù)如下所示 -

ServletContextListener創(chuàng)建項(xiàng)目表的示例

在這個(gè)例子中，我們創(chuàng)建一個(gè)項(xiàng)目所使用的表。因此不需要在數(shù)據(jù)庫中手動(dòng)創(chuàng)建所有表。

修改上面MyListener.java中的示例代碼：

package com.yiibai;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * Application Lifecycle Listener implementation class MyListener
 *
 */
@WebListener
public class MyListener implements ServletContextListener {

    public void contextInitialized(ServletContextEvent event) {

        String jdbcDriver = "com.mysql.jdbc.Driver";
        String dbURL = "jdbc:mysql://localhost/testdb";

        // Database credentials
        String dbUser = "root";
        final String passwd = "123456";
        try {
            Class.forName(jdbcDriver);
            Connection con = DriverManager.getConnection(dbURL, dbUser, passwd);
            String query="CREATE TABLE `employees` (" + 
                    "  `id` int(10) unsigned NOT NULL AUTO_INCREMENT," + 
                    "  `name` varchar(64) NOT NULL DEFAULT ''," + 
                    "  `age` int(3) unsigned NOT NULL DEFAULT '0'," + 
                    "  `address` varchar(254) DEFAULT NULL," + 
                    "  `salary` float(8,2) unsigned DEFAULT NULL," + 
                    "  PRIMARY KEY (`id`)" + 
                    ") ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;";  
            PreparedStatement ps=con.prepareStatement(query);  
            ps.executeUpdate();  

            System.out.println(query);  

            // storing connection object as an attribute in ServletContext
            ServletContext ctx = event.getServletContext();
            ctx.setAttribute("mycon", con);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void contextDestroyed(ServletContextEvent arg0) {
        System.out.println("Servlet has contextDestroyed...");
    }

}

ServletContextListener的其他示例

高性能ServletContextListener的示例

上一篇：Servlet增刪改查下一篇：Servlet ServletInputStream類

在线观看不卡亚洲电影_亚洲妓女99综合网_91青青青亚洲娱乐在线观看_日韩无码高清综合久久

Servlet ServletContextEvent事件

ServletContextEvent和ServletContextListener的示例

ServletContextListener創(chuàng)建項(xiàng)目表的示例