一、Servlet体系结构介绍

在开发中需要继承抽象类HttpServlet
1、Servlet主体关系如下：

2、Servlet需要初始化，那么就需要有初始化参数。这时就得有配置对象：ServletConfig
3、Servlet需要运行，需要运行环境，需要一个上下文对象：ServletContext
4、Servlet要获取客户端的请求，就需要一个请求对象：ServletRequest
5、Servlet要获向客户端响应消息，就需要一个响应对象对象：ServletRespons

二、获取Servlet的初始化参数

1.配置web.xml

如下图所示找到web.xml

开始配置
配置如下：

<?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>Demo01</display-name>
  <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>
  <servlet-name>init</servlet-name>
  <servlet-class>com.et.InitServlet</servlet-class>
  <init-param>
  <param-name>name</param-name>
  <param-value>jack</param-value>
  </init-param>
  </servlet>
  <servlet-mapping>
  <servlet-name>init</servlet-name>
  <url-pattern>/init</url-pattern>
  </servlet-mapping>
</web-app>

2.编写Servlet获取初始化参数

代码如下：

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class InitServlet extends HttpServlet{
	

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	// 重写service方法
	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String name = this.getInitParameter("name");
		PrintWriter writer = response.getWriter();
		writer.println(name);
	}

}