Javaweb中，使用Servlet编写简单的接口

案例：网页提交用户名和密码信息，后端校验密码长度需在6-12位之间

1. 后端部分

   @WebServlet("/valid")
   public class SimpleServlet extends HttpServlet{
   	public void service(HttpServletRequest req, HttpServletResponse resp) throws IOException{
   		// 获取请求参数
   		String username = req.getParameter("username");
   		String password = req.getParameter("password");
   		// 校验密码长度需在6-12位之间
   		String result = "NO";
   		if (password.length() >= 6 && password.length() <= 12) {
   			result = "YES";
   		}
   		// 将结果写入到响应体中
   		PrintWriter writer = resp.getWriter();
   		writer.write(result);
   	}
   }
   

2. 前端部分

   <form action="valid" method="post">
   	<div>
   		<span>用户名：</span>
   		<input type="text" name="username">
   	</div>
   	<div>
   		<span>密码：</span>
   		<input type="password" name="password">
   	</div>
   	<button type="submit">提交</button>
   </form>