web.xml中数据库连接配置：

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns:xsi=""

xmlns="" xmlns:web=""

xsi:schemaLocation=" "

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();

    }

   }

}

}