public class RequestServlet extends HttpServlet {
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
     resp.setContentType("text/html;charset=utf-8");
   // 接收参数
    String value = req.getParameter("username");
    System.out.println(value);
    //向浏览器回写数据
    resp.getWriter().print("data:"+value);
    
    resp.getWriter().print("你好");
  }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
 <!-- 使用servlet标签 -->
 <servlet>
   <servlet-name>HelloServlet</servlet-name>
   <servlet-class>cn.itcast.a_hello.HelloServlet</servlet-class>
 </servlet>
 <servlet>
   <servlet-name>RequestServlet</servlet-name>
   <servlet-class>cn.itcast.b_request.RequestServlet</servlet-class>
 </servlet>
 <!-- 绑定路径 -->
 <servlet-mapping>
   <servlet-name>HelloServlet</servlet-name>
   <url-pattern>/hello</url-pattern>
 </servlet-mapping>
 <servlet-mapping>
   <servlet-name>RequestServlet</servlet-name>
   <url-pattern>/request</url-pattern>
 </servlet-mapping>
</web-app>