1 package cn.itcast; 2  3 import java.io.IOException; 4 import java.io.PrintWriter; 5  6 import javax.servlet.ServletException; 7 import javax.servlet.http.HttpServlet; 8 import javax.servlet.http.HttpServletRequest; 9 import javax.servlet.http.HttpServletResponse;10 11 //servlet调用其他程序，在其他程序中何如读取资源文件（通过类装载器）12 public class ServletDemo3 extends HttpServlet {13 14     15     public void doGet(HttpServletRequest request, HttpServletResponse response)16             throws ServletException, IOException {17         18         UserDao dao = new UserDao();19         dao.find();20         21     }22 23     24     public void doPost(HttpServletRequest request, HttpServletResponse response)25             throws ServletException, IOException {26 27         28     }29 30 }

 1 package cn.itcast; 2  3 import java.io.FileInputStream; 4 import java.io.FileNotFoundException; 5 import java.io.IOException; 6 import java.io.InputStream; 7 import java.util.Properties; 8  9 //如果读取资源文件的程序不是servlet的话，就只能通过类装载器去读10 public class UserDao {11 12     private static Properties dbconfig = new Properties();13     static {14         InputStream in = UserDao.class.getClassLoader().getResourceAsStream(15                 "db.properties");16         try {17             dbconfig.load(in);18         } catch (IOException e) {19             throw new ExceptionInInitializerError(e);20         }21     }22     //以下代码虽然可以读取资源文件数据，但是无法获取更新后的数据23     public void update() throws IOException {24 25         System.out.println(dbconfig.getProperty("url"));26     }27 28     //通过类装载的方式得到资源文件位置，再通过传统方式读取资源文件的数据，这样可以读取更新后的数据29     public void find() throws IOException {30         String path = UserDao.class.getClassLoader().getResource("db.properties").getPath();31         FileInputStream in = new FileInputStream(path);32 33         Properties dbconfig = new Properties();34         dbconfig.load(in);35 36         System.out.println(dbconfig.getProperty("url"));37 38     }39 40 }

 1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app version="2.4"  3     xmlns="http://java.sun.com/xml/ns/j2ee"  4     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  5     xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee  6     http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> 7      8 <servlet> 9     <servlet-name>ServletDemo1</servlet-name>10     <servlet-class>cn.itcast.ServletDemo1</servlet-class>11 </servlet>12   <servlet>13     <servlet-name>ServletDemo3</servlet-name>14     <servlet-class>cn.itcast.ServletDemo3</servlet-class>15   </servlet>16 17 18 19 <servlet-mapping>20     <servlet-name>ServletDemo1</servlet-name>21     <url-pattern>/ServletDemo1</url-pattern>22 </servlet-mapping>23   <servlet-mapping>24     <servlet-name>ServletDemo3</servlet-name>25     <url-pattern>/servlet/ServletDemo3</url-pattern>26   </servlet-mapping>27     28   <welcome-file-list>29     <welcome-file>index.jsp</welcome-file>30   </welcome-file-list>31 </web-app>