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 + "	characterEncoding="
                + 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：