ServletConfig概述

1、容器初始化一个servlet时，会为这个servlet建一个唯一的ServletConfig
2、容器从web.xml读出Servlet初始化参数，并把这些参数交给ServletConfig，然后把ServletConfig传递给servlet的init(ServletConfig config)方法。
3、容器只有在创建servlet实例时才会读DD文件中的init-param, 并且在servlet一生中只读一次。
4、方法:
getInitParameter(String name)：根据给定的初始化参数，返回匹配的初始化参数值。
getInitParameterNames()：返回一个Enumeration对象，里面包含了所有的初始化参数。
getServletContext()：返回一个servletContext()对象.
getServletName()：返回servlet的名字，即web.xml中的的子元素的值。如果没有配置这个子元素，则返回servlet类的名字。

getInitParameter()的使用

web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>MyServlet</display-name> //文件名
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <!-- 类名 -->  
   <servlet-name>Myservlet</servlet-name> //类名
    <!-- 所在的包.类名--> 
   <servlet-class>servlet.com.Myservlet</servlet-class>   
     <init-param>
      <param-name>name</param-name>
      <param-value>admin</param-value>
    </init-param>
       <init-param>
      <param-name>psd</param-name>
      <param-value>123456</param-value>
    </init-param>
  </servlet>
  
 <servlet-mapping> 
  <servlet-name>Myservlet</servlet-name> //类名
  <url-pattern>/Myservlet/Myservlet</url-pattern>   路径:/项目名/类名
  </servlet-mapping> 
  
</web-app>

Myservlet.java源码

package servlet.com;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Myservlet
 */
//@WebServlet(
//		asyncSupported = true, 
//		urlPatterns = { "/Myservlet" }, 
//		initParams = { 
//				@WebInitParam(name = "name", value = "admin"), 
//				@WebInitParam(name = "psd", value = "123456")
//		}
//		)

//@WebServlet("/Myservlet")  
public class Myservlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public Myservlet() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		//response.getWriter().append("Served at: ").append(request.getContextPath());
		
		 PrintWriter out = response.getWriter();
		 response.setHeader("Content-type","text/html; charset=UTF-8");
		 ServletConfig cfg = getServletConfig();
		 String username  = cfg.getInitParameter("name");
		 String password  = cfg.getInitParameter("psd");
	     out.println("name: "+username);
	     out.println("psd: "+password);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}