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ServletContextListener的用法和實例

ServletContextListener：
馬克- to-win：馬克 java社區(qū)：防盜版實名手機(jī)尾號： 73203。
ServletContextListener能監(jiān)聽到你的應(yīng)用程序的啟動和銷毀。

例 2.2.1.1

package com;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class MyServletContextListener implements
ServletContextListener {
    public void contextDestroyed(ServletContextEvent arg0) {
        System.out.println("Destroyed 被執(zhí)行");
    }
    public void contextInitialized(ServletContextEvent arg0) {
        ServletContext sc=arg0.getServletContext();
        System.out.println("馬克-to-win Initialized 被執(zhí)行"+sc.getMajorVersion());
    }
}



web.xml中加入一段話：

  <listener>
    <listener-class>com.MyServletContextListener</listener-class>
  </listener>


隨便運行一個servlet或jsp，啟動tomcat的過程中，你可以發(fā)現(xiàn)在console中其中有這么一段話：

馬克-to-win Initialized 被執(zhí)行2

隨便改動一個java文件，一保存，應(yīng)用程序被重新加載，過去的應(yīng)用被卸載，于是contextDestroyed被執(zhí)行。console當(dāng)中也會出現(xiàn)下面的話：

Destroyed 被執(zhí)行

例 2.2.1.2

下面是Listener的一個實際應(yīng)用，和單態(tài)數(shù)據(jù)源應(yīng)用相比，Listener數(shù)據(jù)源是啟動你的web應(yīng)用時啟動的，不是第一個用戶訪問時啟動的，對于用戶來講，體驗會好一點。但有沒有人訪問，都會啟動數(shù)據(jù)源。


package com;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource;
public class MyServletContextListener implements ServletContextListener {
    public void contextDestroyed(ServletContextEvent arg0) {
        ServletContext context = arg0.getServletContext();
        MysqlConnectionPoolDataSource ds=(MysqlConnectionPoolDataSource)context.getAttribute("mysqlds");
/*參見java第三章的內(nèi)存泄露*/       
        ds=null;
        context.removeAttribute("mysqlds");
        System.out.println("Destroyed 被執(zhí)行");
    }
    public void contextInitialized(ServletContextEvent arg0) {
        ServletContext context = arg0.getServletContext();
        DBConForListener con = new DBConForListener();
        MysqlConnectionPoolDataSource ds = con.getDs();
        context.setAttribute("mysqlds", ds);
        System.out.println("contextInitialized3");
    }
}

package com;
import com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource;
public class DBConForListener {
    private MysqlConnectionPoolDataSource ds;
    public DBConForListener() {
        ds = new MysqlConnectionPoolDataSource();
        ds.setURL("jdbc:mysql://localhost:3306/test");
        ds.setUser("root");
        ds.setPassword("1234");
    }
    public MysqlConnectionPoolDataSource getDs() {
        return ds;
    }
}





package com;
import java.io.IOException;
import java.sql.*;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.mysql.jdbc.jdbc2.optional.MysqlConnectionPoolDataSource;

public class ServletHello1 extends HttpServlet {
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        ServletContext sc = this.getServletContext();
        MysqlConnectionPoolDataSource ds = (MysqlConnectionPoolDataSource) sc
                .getAttribute("mysqlds");
        Connection con;
        try {
            con = ds.getConnection();
            Statement stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("select * from login");
            while (rs.next()) {
                System.out.println(rs.getString("id"));
                System.out.println(rs.getString("name"));
            }
            rs.close();
            stmt.close();
            con.close();
            System.out.println("ok");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}


運行servlet，console當(dāng)中輸出的結(jié)果是：

1
q
2
qq
2.5
qqq
3
qqq
ok