主页面t2.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>include动作--不带参数</title>
</head>
<body>
<div style="text-align:center">

<h1>请输入一个正数，单击按钮求这个数的平方根。</h1>
<hr>
<jsp:include page="t2_ok.jsp" />

</div>
</body>
</html>

辅页面t2_ok.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
</head>
<body>
<%  

   double num = 0;

   String str=request.getParameter("num");

   try{

		if(str!=null){

		num = Double.parseDouble(str);

		}else{

		out.println("【提示：】请输入数据，谢谢！");

		}

   	} catch(Exception e){

               out.println("只能输入数字") ;

              }

%>

<p>请输入一个数字，谢谢！</p>

<form action="#" method="post" name="form">

<input type="text" name="num"><br><br>

<input type="submit" name="submit" value="开始计算">

</form>

<p><%=num%>的平方根是:<%=Math.sqrt(num)%></p>

</body>
</html>