servletConfig的应用

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：
获得字符集编码
获得数据库连接信息
获得配置文件 ，查看struts案例的web.xml文件

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. <servlet-mapping>
38. <servlet-name>DemoServlet</servlet-name>
39. <url-pattern>/demo/*</url-pattern>
40. </servlet-mapping>
41. <servlet-mapping>
42. <servlet-name>DemoServlet</servlet-name>
43. <url-pattern>*.do</url-pattern>
44. </servlet-mapping>
45. <welcome-file-list>
46. <welcome-file>index.html</welcome-file>
47. </welcome-file-list>
48. </web-app>

1. package cn.csdn.web.servlet;
2. import java.io.IOException;
3. import java.io.PrintWriter;
4. import java.util.Enumeration;
5. import javax.servlet.ServletConfig;
6. import javax.servlet.ServletException;
7. import javax.servlet.http.HttpServlet;
8. import javax.servlet.http.HttpServletRequest;
9. import javax.servlet.http.HttpServletResponse;
10. public class DemoServlet extends HttpServlet {
11. /**
12. * @author 宋鹤贤
13. */
14. private static final long serialVersionUID = 1L;
15. /* private ServletConfig config; */
16. @Override
17. public void destroy() {
18. // TODO Auto-generated method stub
19. super.destroy();
20. System.out.println("销毁");
21. }
22. public DemoServlet() {
23. super();
24. // TODO Auto-generated constructor stub
25. System.out.println("创建对象");
26. }
27. @Override
28. public void init() throws ServletException {
29. // TODO Auto-generated method stub
30. super.init();
31. System.out.println("初始化");
32. }
33. @Override /*HttpServlet父类有两个init方法，一个有参一个没参数*/
34. public void init(ServletConfig config) throws ServletException {
35. super.init(config);
36. System.out.println("--------------" + config);
37. /* this.config=config; */
38. }
39. public void doGet(HttpServletRequest request, HttpServletResponse response)
40. throws ServletException, IOException {
41. this.doPost(request, response);
42. }
43. public void doPost(HttpServletRequest request, HttpServletResponse response)
44. throws ServletException, IOException {
45. /* 设置编码 */
46. request.setCharacterEncoding("UTF-8");
47. String version = this.getServletConfig().getInitParameter("version");
48. String characterEncoding = this.getServletConfig().getInitParameter(
49. "characterEncoding");
50. Enumeration<String> enumer = this.getServletConfig()
51. .getInitParameterNames();
52. // 遍历
53. while (enumer.hasMoreElements()) {
54. String name = enumer.nextElement();
55. String value = this.getServletConfig().getInitParameter(name);
56. System.out.println(name + "===" + value);
57. }
58. /* 获取一下PrintWriter对象 */
59. PrintWriter out = response.getWriter();
60. out.print("versin=" + version + "\tcharacterEncoding="
61. + characterEncoding);
62. }
63. }

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：