Servlet读取xml文件的配置参数

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>

web.xml

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();

     }

    }

 }

 }

Servlet