public class HelloWorld extends HttpServlet {
public void service(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
response.setContentType("text/html");//告诉服务器是html
PrintWriter out = response.getWriter();
out.println("

Hello World

            }
        }
        xml的写法：（在tomcat安装目录下有很多例子）
            <web-app>
                <servlet>
                    <servlet-name>HelloWorld</servlet-name>
                    <servlet-class>first.HelloWorld</servlet-class>
                </servlet>
                <servlet-mapping>
                    <servlet-name>HelloWorld</servlet-name>
                    <url-pattern>/sayHello</url-pattern>
                </servlet-mapping>
            </web-app>

用Servlet原生写也可以啊

用原生的要怎么写，servlet太久没用了