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

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<display-name></display-name>
<servlet>
<servlet-name>DemoServlet</servlet-name>
<servlet-class>cn.csdn.web.servlet.DemoServlet</servlet-class>
<init-param>
<param-name>version</param-name>
<param-value>2.0</param-value>
</init-param>
<init-param>
<param-name>characterEncoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
<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:3306/3g</param-value>
</init-param>
<init-param>
<param-name>user</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>password</param-name>
<param-value>0904</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>DemoServlet</servlet-name>
<url-pattern>/demo/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>DemoServlet</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
</welcome-file-list>
</web-app>

package cn.csdn.web.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Enumeration;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DemoServlet extends HttpServlet {
/**
* @author 宋鹤贤
*/
private static final long serialVersionUID = 1L;
/* private ServletConfig config; */
@Override
public void destroy() {
// TODO Auto-generated method stub
super.destroy();
System.out.println("销毁");
}
public DemoServlet() {
super();
// TODO Auto-generated constructor stub
System.out.println("创建对象");
}
@Override
public void init() throws ServletException {
// TODO Auto-generated method stub
super.init();
System.out.println("初始化");
}
@Override /*HttpServlet父类有两个init方法，一个有参一个没参数*/
public void init(ServletConfig config) throws ServletException {
super.init(config);
System.out.println("--------------" + config);
/* this.config=config; */
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
/* 设置编码 */
request.setCharacterEncoding("UTF-8");
String version = this.getServletConfig().getInitParameter("version");
String characterEncoding = this.getServletConfig().getInitParameter(
"characterEncoding");
Enumeration<String> enumer = this.getServletConfig()
.getInitParameterNames();
// 遍历
while (enumer.hasMoreElements()) {
String name = enumer.nextElement();
String value = this.getServletConfig().getInitParameter(name);
System.out.println(name + "===" + value);
}
/* 获取一下PrintWriter对象 */
PrintWriter out = response.getWriter();
out.print("versin=" + version + "\tcharacterEncoding="
+ characterEncoding);
}
}

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：

巴特西

servletConfig的应用

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