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>