想问一下出现这样的错误是什么原因？

jsp中为什么使用param会报错，是和forward一起使用的，如下图错误

value必须是个确定的值，不能夹代码

img


点击提交后就报错了，如上图的错误，求大神解答


calculate.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html" charset="UTF-8">
    <title>计算器</title>
    <style>
        #kuang{
            height:20px;
            width:170px;
            border:1px solid #000000;
            position: absolute;
            top:53px;
            left:400px;
            border-radius:2px ;
        }
    </style>
</head>
<body>
    <%
        String number1str =request.getParameter("number1");
        String number2str=request.getParameter("number2");
        String operator=request.getParameter("operator");
        String sum=request. getParameter("sum");
        if(number1str==null || number2str==null || operator==null){
        number1str="";
        number2str="";
        operator="+";
        sum="";
        }


    %>
    <h3>计算器</h3>
    <form name = "form" action="docalculate.jsp" method="get" >
        <input type="text" name="number1" value="<%=request.getParameter("number1")%>">
        <select name="operator">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="×">×</option>
            <option value="÷">÷</option>
        </select>
        <input type="text" name="number2" value="<%=request.getParameter("number2")%>"> =
        <div id="kuang">\
            <%
                request.getParameter("sum");
            %>
        </div>
            <br/><br/>
        <input type="submit" value="计算">
    </form>
</body>
</html>

docalculate.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html" charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <%
        double sum=0.0;
        String number1str=request.getParameter("number1");
        String number2str=request.getParameter("number2");
        String operator=request.getParameter("select");
        if(number1str != null && number2str != null && operator != null){
            double number1=Double.parseDouble(number1str);
            double number2=Double.parseDouble(number2str);
            if("+". equals(operator)){
                sum=number1+number2;
                out. print(sum);
            }else if("-". equals(operator)) {
                sum = number1 - number2;
                out.print(sum);
            }else if("*". equals(operator)){
                sum=number1* number2;
                out.print(sum);
            }else if("/". equals(operator)){
                sum=number1/number2;
                out.print(sum);
                }}
    %>
    <jsp:forward page="calculate.jsp">
        <jsp: param name="number1" value="<%=number1str%>"/>
        <jsp: param name="number2" value="<%=number2str%>"/>
        <jsp: param name="sum" value="<%=sum%>"/>
    </jsp:forward>
</body>
</html>