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