Javaweb-ServletConfig

一、ServletConfig对象

1. 在Servlet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；
2. 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initial方法时，将ServletConfig对象传递给servlet，进而程序员通过ServletConfig对象得到当前servlet的初始化参数信息；
3. 样例：

<servlet>
    <servlet-name>Demo5</servlet-name>
    <servlet-class>demo.Demo5</servlet-class>
    <init-param>
        <param-name>data</param-name>
        <param-value>abc</param-value>
    </init-param>
</servlet>

二、实例说明

package demo;

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//@WebServlet("/servlet/Demo5")
public class Demo5 extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public Demo5() {
        super();
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //得到指定的参数信息
          String value =  this.getServletConfig().getInitParameter("data");
          System.out.println(value);

          //当有多个参数时，获取所有的参数信息
          Enumeration e = this.getServletConfig().getInitParameterNames();
          while(e.hasMoreElements()){
              String name = (String) e.nextElement();
              String value1 = this.getServletConfig().getInitParameter(name);
              System.out.println(name + "=" + value);
          }
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            doGet(request, response);
    }

}

三、使用场景

在实际开发中，有些内容不适合在servlet程序中写死，这时我们通过配置文件将这些数据传递给servlet

场景一：servlet采用的编码表

配置文件：

<init-param>
        <param-name>charset</param-name>
        <param-value>UFT-8</param-value>
    </init-param>

场景二：servlet连接的数据库

配置文件：

<init-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/test</param-value>
    </init-param>
    <init-param>
        <param-name>username</param-name>
        <param-value>root</param-value>
    </init-param>
    <init-param>
        <param-name>password</param-name>
        <param-value>root</param-value>
    </init-param>

场景三：servlet读取的配置文件

<init-param>
        <param-name>config</param-name>
        <param-value>/struts-config.xml</param-value>
    </init-param>

• 备注：传智播客视频学习笔记