ServletConfig的含义及使用

转自http://blog.csdn.net/qp3887322/article/details/6944182

在Servlet的配置文件中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。


当servlet配置了初始化参数后，web容器在创建servlet实例对象时，会自动将这些初始化参数封装到ServletConfig对象中，并在调用servlet的init方法时，将ServletConfig对象传递给servlet。进而，程序员通过ServletConfig对象就可以得到当前servlet的初始化参数信息。


阅读ServletConfig API，并举例说明该对象的作用：
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获得数据库连接信息
获得配置文件

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1. <?xmlversion="1.0"encoding="UTF-8"?> 
2. <web-app version="3.0"  
3.     xmlns="http://java.sun.com/xml/ns/javaee"  
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"  
5.     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  
6.     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"> 
7.   <display-name></display-name> 
8.   <servlet> 
9.     <servlet-name>DemoServlet</servlet-name> 
10.     <servlet-class>cn.csdn.web.servlet.DemoServlet</servlet-class> 
11.      <init-param> 
12.         <param-name>version</param-name> 
13.         <param-value>2.0</param-value> 
14.     </init-param>  
15.     <init-param> 
16.         <param-name>characterEncoding</param-name> 
17.         <param-value>UTF-8</param-value> 
18.     </init-param>  
19.     <init-param> 
20.         <param-name>driver</param-name> 
21.         <param-value>com.mysql.jdbc.driver</param-value> 
22.     </init-param>  
23.     <init-param> 
24.         <param-name>url</param-name> 
25.         <param-value>jdbc:mysql://localhost:3306/3g</param-value> 
26.     </init-param>  
27.     <init-param> 
28.         <param-name>user</param-name> 
29.         <param-value>root</param-value> 
30.     </init-param>  
31.     <init-param> 
32.         <param-name>password</param-name> 
33.         <param-value>0904</param-value> 
34.     </init-param>  
35.     <load-on-startup>1</load-on-startup> 
36.   </servlet> 
37.  
38.   <servlet-mapping> 
39.     <servlet-name>DemoServlet</servlet-name> 
40.     <url-pattern>/demo/*</url-pattern> 
41.   </servlet-mapping> 
42.   <servlet-mapping> 
43.     <servlet-name>DemoServlet</servlet-name> 
44.     <url-pattern>*.do</url-pattern> 
45.   </servlet-mapping> 
46.      
47.   <welcome-file-list> 
48.     <welcome-file>index.html</welcome-file> 
49.   </welcome-file-list> 
50. </web-app> 

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1. <?xml version="1.0" encoding="UTF-8"?>  
2. <web-app version="3.0"   
3.     xmlns="http://java.sun.com/xml/ns/javaee"   
4.     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"   
5.     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   
6.     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">  
7.   <display-name></display-name>  
8.   <servlet>  
9.     <servlet-name>DemoServlet</servlet-name>  
10.     <servlet-class>cn.csdn.web.servlet.DemoServlet</servlet-class>  
11.      <init-param>  
12.         <param-name>version</param-name>  
13.         <param-value>2.0</param-value>  
14.     </init-param>   
15.     <init-param>  
16.         <param-name>characterEncoding</param-name>  
17.         <param-value>UTF-8</param-value>  
18.     </init-param>   
19.     <init-param>  
20.         <param-name>driver</param-name>  
21.         <param-value>com.mysql.jdbc.driver</param-value>  
22.     </init-param>   
23.     <init-param>  
24.         <param-name>url</param-name>  
25.         <param-value>jdbc:mysql://localhost:3306/3g</param-value>  
26.     </init-param>   
27.     <init-param>  
28.         <param-name>user</param-name>  
29.         <param-value>root</param-value>  
30.     </init-param>   
31.     <init-param>  
32.         <param-name>password</param-name>  
33.         <param-value>0904</param-value>  
34.     </init-param>   
35.     <load-on-startup>1</load-on-startup>  
36.   </servlet>  
37.   
38.   <servlet-mapping>  
39.     <servlet-name>DemoServlet</servlet-name>  
40.     <url-pattern>/demo/*</url-pattern>  
41.   </servlet-mapping>  
42.   <servlet-mapping>  
43.     <servlet-name>DemoServlet</servlet-name>  
44.     <url-pattern>*.do</url-pattern>  
45.   </servlet-mapping>  
46.       
47.   <welcome-file-list>  
48.     <welcome-file>index.html</welcome-file>  
49.   </welcome-file-list>  
50. </web-app>  

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1. package cn.csdn.web.servlet; 
2.  
3. import java.io.IOException; 
4. import java.io.PrintWriter; 
5. import java.util.Enumeration; 
6. import javax.servlet.ServletConfig; 
7. import javax.servlet.ServletException; 
8. import javax.servlet.http.HttpServlet; 
9. import javax.servlet.http.HttpServletRequest; 
10. import javax.servlet.http.HttpServletResponse; 
11.  
12. public class DemoServletextends HttpServlet { 
13.  
14.     /**
15.      * @author 宋鹤贤
16.      */ 
17.  
18.     private staticfinallong serialVersionUID = 1L; 
19.  
20.     /* private ServletConfig config; */ 
21.  
22.     @Override 
23.     public void destroy() { 
24.         // TODO Auto-generated method stub 
25.         super.destroy(); 
26.         System.out.println("销毁"); 
27.     } 
28.  
29.     public DemoServlet() { 
30.         super(); 
31.         // TODO Auto-generated constructor stub 
32.         System.out.println("创建对象"); 
33.     } 
34.  
35.     @Override 
36.     public void init()throws ServletException { 
37.         // TODO Auto-generated method stub 
38.         super.init(); 
39.         System.out.println("初始化"); 
40.     } 
41.  
42.     @Override 
43.     public void init(ServletConfig config)throws ServletException { 
44.         super.init(config); 
45.         System.out.println("--------------" + config); 
46.         /* this.config=config; */ 
47.     } 
48.  
49.     public void doGet(HttpServletRequest request, HttpServletResponse response) 
50.             throws ServletException, IOException { 
51.         this.doPost(request, response); 
52.     } 
53.  
54.     public void doPost(HttpServletRequest request, HttpServletResponse response) 
55.             throws ServletException, IOException { 
56.         /* 设置编码 */ 
57.         request.setCharacterEncoding("UTF-8"); 
58.         String version = this.getServletConfig().getInitParameter("version"); 
59.         String characterEncoding = this.getServletConfig().getInitParameter( 
60.                 "characterEncoding"); 
61.  
62.         Enumeration<String> enumer = this.getServletConfig() 
63.                 .getInitParameterNames(); 
64.         // 遍历 
65.  
66.         while (enumer.hasMoreElements()) { 
67.             String name = enumer.nextElement(); 
68.             String value = this.getServletConfig().getInitParameter(name); 
69.             System.out.println(name + "===" + value); 
70.         } 
71.  
72.         /* 获取一下PrintWriter对象 */ 
73.         PrintWriter out = response.getWriter(); 
74.         out.print("versin=" + version +"\tcharacterEncoding=" 
75.                 + characterEncoding); 
76.     } 
77.  
78. } 

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1. package cn.csdn.web.servlet;  
2.   
3. import java.io.IOException;  
4. import java.io.PrintWriter;  
5. import java.util.Enumeration;  
6. import javax.servlet.ServletConfig;  
7. import javax.servlet.ServletException;  
8. import javax.servlet.http.HttpServlet;  
9. import javax.servlet.http.HttpServletRequest;  
10. import javax.servlet.http.HttpServletResponse;  
11.   
12. public class DemoServlet extends HttpServlet {  
13.   
14.     /** 
15.      * @author 宋鹤贤 
16.      */  
17.   
18.     private static final long serialVersionUID = 1L;  
19.   
20.     /* private ServletConfig config; */  
21.   
22.     @Override  
23.     public void destroy() {  
24.         // TODO Auto-generated method stub  
25.         super.destroy();  
26.         System.out.println("销毁");  
27.     }  
28.   
29.     public DemoServlet() {  
30.         super();  
31.         // TODO Auto-generated constructor stub  
32.         System.out.println("创建对象");  
33.     }  
34.   
35.     @Override  
36.     public void init() throws ServletException {  
37.         // TODO Auto-generated method stub  
38.         super.init();  
39.         System.out.println("初始化");  
40.     }  
41.   
42.     @Override  
43.     public void init(ServletConfig config) throws ServletException {  
44.         super.init(config);  
45.         System.out.println("--------------" + config);  
46.         /* this.config=config; */  
47.     }  
48.   
49.     public void doGet(HttpServletRequest request, HttpServletResponse response)  
50.             throws ServletException, IOException {  
51.         this.doPost(request, response);  
52.     }  
53.   
54.     public void doPost(HttpServletRequest request, HttpServletResponse response)  
55.             throws ServletException, IOException {  
56.         /* 设置编码 */  
57.         request.setCharacterEncoding("UTF-8");  
58.         String version = this.getServletConfig().getInitParameter("version");  
59.         String characterEncoding = this.getServletConfig().getInitParameter(  
60.                 "characterEncoding");  
61.   
62.         Enumeration<String> enumer = this.getServletConfig()  
63.                 .getInitParameterNames();  
64.         // 遍历  
65.   
66.         while (enumer.hasMoreElements()) {  
67.             String name = enumer.nextElement();  
68.             String value = this.getServletConfig().getInitParameter(name);  
69.             System.out.println(name + "===" + value);  
70.         }  
71.   
72.         /* 获取一下PrintWriter对象 */  
73.         PrintWriter out = response.getWriter();  
74.         out.print("versin=" + version + "\tcharacterEncoding="  
75.                 + characterEncoding);  
76.     }  
77.   
78. }  

代码如上：我们发布到tomcat中，然后开启tomcat服务器，在浏览器中输入http://localhost:8080/20111018/xxx.do，界面返回结果如下：