Servlet3.0版本之后，推出了Servlet基于注解式开发。
优点：开发效率高，直接在java类上使用注解进行标注，可直接省略WEB.xml文件配置

import javax.servlet.annotation.WebServlet;

@WebServlet

@WebServlet的属性

name属性：用来指定Servlet的名字 == <servlet-name>

urlPatterns属性：用来指定Servlet的映射路径。可以指定多个路径 == <url-pattern>

loadOnstartUp属性：用来指定在服务器启动阶段是否加载该类。 == <load-on-startup>

value属性：和urlPatterns属性一样，都是用来指定Servlet映射路径(若使用value，则属性名可以省略)

@WebServlet(name ="demo" ,urlPatterns = {"/qgs/demoServlet1","/qgs/demoServlet2"}, loadOnStartup = 1,

        initParams = {@WebInitParam(name ="demo1",value = "111"),@WebInitParam(name ="demo2",value = "222")})

public class DemoServlet extends HttpServlet {

    @Override

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType("text/html;charset=UTF-8");

        PrintWriter out = response.getWriter();

        //获取初始化参数

        Enumeration<String> Names = request.getParameterNames();

        while (Names.hasMoreElements()) {

            String name = Names.nextElement();

            String value = getInitParameter(name);

        }

        out.print("hello world :"+request.getContextPath());

    }

}