Servlet 读取web.xml文件中的配置参数连接数据库

http://hi.baidu.com/yych13/item/6a1c1b15334148098ebde431

web.xml中数据库连接配置：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
id="WebApp_ID" version="2.5">
<display-name>Servelt_ReadingDBFromWebXml</display-name>
<welcome-file-list>
   <welcome-file>index.html</welcome-file>
   <welcome-file>index.htm</welcome-file>
   <welcome-file>index.jsp</welcome-file>
   <welcome-file>default.html</welcome-file>
   <welcome-file>default.htm</welcome-file>
   <welcome-file>default.jsp</welcome-file>
</welcome-file-list>
<!-- 通过getServletContext().getInitParameter("XX")读取 -->
<context-param>
   <param-name>driver</param-name>
   <param-value>com.mysql.jdbc.Driver</param-value>
</context-param>
<context-param>
   <param-name>url</param-name>
   <param-value>jdbc:mysql://localhost:3306/sample</param-value>
</context-param>
<context-param>
   <param-name>username</param-name>
   <param-value>root</param-value>
</context-param>
<context-param>
   <param-name>password</param-name>
   <param-value>admin</param-value>
</context-param>
<servlet>
   <servlet-name>DBServlet</servlet-name>
   <servlet-class>demo.DBServlet</servlet-class>
   <!-- 通过getServletConfig().getInitParameter("XX")读取 -->
   <init-param>
    <param-name>driver</param-name>
    <param-value>com.mysql.jdbc.Driver</param-value>
   </init-param>
   <init-param>
    <param-name>url</param-name>
    <param-value>jdbc:mysql://localhost:3306/sample</param-value>
   </init-param>
   <init-param>
    <param-name>username</param-name>
    <param-value>root</param-value>
   </init-param>
   <init-param>
    <param-name>password</param-name>
    <param-value>admin</param-value>
   </init-param>
</servlet>
<servlet-mapping>
   <servlet-name>DBServlet</servlet-name>
   <url-pattern>/readingDB</url-pattern>
</servlet-mapping>
</web-app>

Servlet代码：
/**
*
*/

package demo;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Reading DB Config from web.xml
*/
public class DBServlet extends HttpServlet {
/**
* 
*/
private static final long serialVersionUID = 1L;
private String diverClass;
private String userName;
private String password;
private String url;
@Override
public void init() throws ServletException {
   diverClass = /* getServletConfig(). */getServletContext().getInitParameter("driver");
   userName = /* getServletConfig(). */getServletContext().getInitParameter("username");
   password = /* getServletConfig(). */getServletContext().getInitParameter("password");
   url = /* getServletConfig(). */getServletContext().getInitParameter("url");
   try {
    Class.forName(diverClass);
   } catch (Exception e) {
    e.printStackTrace();
   }
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
   Connection connection = null;
   PreparedStatement statement = null;
   try {
    connection = DriverManager.getConnection(url, userName, password);
    statement = connection.prepareStatement("select * from customer");
    ResultSet rs = statement.executeQuery();
    PrintWriter printWriter = resp.getWriter();
    while (rs.next()) {
     printWriter.println(rs.getString("id"));
     printWriter.println(rs.getString("name"));
    }
   } catch (SQLException e) {
    e.printStackTrace();
   } finally {
    try {
     if (statement != null) {
      statement.close();
     }
     if (connection != null) {
      connection.close();
     }
    } catch (SQLException e) {
     e.printStackTrace();
    }
   }
}
}