Question

我正在使用Eclipse工作JSP项目。我尝试从我在JSP中创建的方法/函数进行一些计算，但是它仍然显示Sum，Sub和＆amp;的初始化值为0.0。当按下按钮而不是从输入标签获取输入然后进行计算时，Mul。以下是我目前的代码：

<pre><code>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="java.io.*" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<%!     
public double add(double a, double b) {

    return a + b;
}

public double subtract(double a, double b) {

    return a - b;
}

public double multiply(double a, double b) {

    return a * b;
}   
%>

<%
    PrintWriter Out = response.getWriter();

    double Sum = 0.0, Sub = 0.0, Mul = 0.0;

    if (request.getParameter("stNum") != null  && request.getParameter("ndNum") !=     null) {

        Sum = add(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
        Sub = subtract(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
        Mul = multiply(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
    }

    //Sum = add(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
    //Sub = subtract(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
    //Mul = multiply(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));
%>

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>JSP Mathematics Calculations !!!</title>
</head>
<body>
    <label>Enter the first number: </label><input type="text" id="stNum" name="stNum" width="30" />

    <br />
    <br />

    <label>Enter the second number: </label><input type="text" id="ndNum" name="ndNum" width="30" />

    <br />
    <br />

    <input type="button" value="Sum" onclick="alert('The sum is: <%=Sum %>');" />

    <br />
    <br />

    <input type="button" value="Subtract" onclick="alert('The subtraction is: <%=Sub %>');" />

    <br />
    <br />

    <input type="button" value="Multiplication" onclick="alert('The multiplication is: <%=Mul %>');" />
</body>
</html>
</code></pre>

请帮忙。谢谢。

Answer 1

您的输入元素不在<form>标记内！

如何在没有表单的情况下提交页面。您是否在问题中提供了确切的HTML？

应该是，

<body>
<form method="POST" action="page_url">
    <label>Enter the first number: </label><input type="text" id="stNum" name="stNum" width="30" />

    <br />
    <br />

    <label>Enter the second number: </label><input type="text" id="ndNum" name="ndNum" width="30" />

    <br />
    <br />

    <input type="button" value="Sum" onclick="alert('The sum is: <%=Sum %>');" />

    <br />
    <br />

    <input type="button" value="Subtract" onclick="alert('The subtraction is: <%=Sub %>');" />

    <br />
    <br />

    <input type="button" value="Multiplication" onclick="alert('The multiplication is: <%=Mul %>');" />
</form>
</body>

Answer 2

将所有输入参数放在表单中，然后按下按钮执行操作：

<form method="POST" action="page_url">
   <label>Enter the first number: </label><input type="text" id="stNum" name="stNum" width="30" />

   <br />
   <br />
   <label>Enter the second number: </label><input type="text" id="ndNum" name="ndNum" width="30" />

   <br />
   <br />

   <input type="button" value="Sum" name="sum" />

   <br />
   <br />

   <input type="button" value="Subtract" nam="dif" />

   <br />
   <br />

   <input type="button" value="Multiplication" name="mul" />
   <%
   if(request.getParameter("sum")!=null)
   {
        Sum = add(Double.parseDouble(request.getParameter("stNum")), Double.parseDouble(request.getParameter("ndNum")));

   }%>
       <script>
           alert("The sum is "+Sum);
       </script>
   <%
   .....//Similarly for subtraction and multiplication
    %>
</form>

JSP项目 - 没有采用输入标记的双精度值

2 个答案: