如何用 MySQL 数据库中的数据填写 jsp 表格？

Question

我有一个 jsp 页面，其中有一个从数据库中填充的一些产品的下拉列表。我想要的是，当用户选择产品时，我希望从数据库中自动填充费率字段。我的 jsp 页面：

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html, charset=utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">

<script src="http://code.jquery.com/jquery-1.8.3.js"></script>
<script src="http://code.jquery.com/ui/1.9.2/jquery-ui.js"></script>
<link rel="stylesheet" href="http://code.jquery.com/ui/1.9.2/themes/base/jquery-ui.css" />

<title>Purchase new product </title>
</head>
<body>
<script>
    $(function() {
        $('input[name=date]').datepicker();
     });

     function multiply()
     {
        var q = document.getElementById('quantity').value;
        var r = document.getElementById('rateid').value;
        document.getElementById('total').value = q*r;
     }
</script>
<div class="container">
<h1>Place your order:</h1><br/>
    <form method="post" action="PurchaseController" name="pform"> 
    <table class="table table-striped table-hover table-condensed table-bordered">
    <tr>
        <td>Product:</td>
        <td><select name="selectedProduct">
                <option value=0>Select one</option>
                    <c:forEach items="${product}" var="product">
                        <option value="${product.pid}"><c:out value="${product.name}" /> </option>
                    </c:forEach>
                </select> 
        </td>
    </tr>
    <tr>
        <td>Quantity:</td>
        <td><input type="number" name="quantity" id="quantity" oninput="multiply()" 
             onkeypress="return event.charCode >=48" min="1" required>
            </td>
        </tr>
        <tr>
            <td>Rate:</td>
            <td><input type="text" name="rate" id="rateid" oninput="multiply()" <%--  value="<c:out value="${product.rate}" />" --%> >
            </td>
        </tr>
        <tr>
            <td>Total:</td>
            <td><input type="number" name="total" id="total" readonly ></td>
        </tr>
        <tr>
            <td>Date:</td>
            <td><input type="text" name="date" placeholder="Date" required></td>
        </tr>
    </table>
    <input type="submit" value="Submit" class="btn btn-primary">
    <input type="reset" value="Reset" class="btn btn-danger">
    </form> 
    <br/>
    <a href="index.jsp">Back to home</a>
</div>
</body>
</html>

当我取消注释上面代码中 "Rate" 字段中的注释部分时，我得到如下 NumberFormatException 错误：

org.apache.jasper.JasperException: An exception occurred processing JSP page [/purchase.jsp] at line [55]

52:         <tr>
53:             <td>Rate:</td>
54:             <td><input type="text" name="rate" id="rateid" oninput="multiply()" 
55:              value="<c:out value="${product.rate}" />" >
56:             </td>
57:         </tr>
58:             <td>Total:</td>


Stacktrace:
    org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:584)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:481)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    com.product.controller.ProductController.doGet(ProductController.java:57)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

Root Cause

java.lang.NumberFormatException: For input string: "rate"
    java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    java.lang.Integer.parseInt(Integer.java:580)
    java.lang.Integer.parseInt(Integer.java:615)
    javax.el.ListELResolver.coerce(ListELResolver.java:150)
    javax.el.ListELResolver.getValue(ListELResolver.java:67)
    org.apache.jasper.el.JasperELResolver.getValue(JasperELResolver.java:110)
    org.apache.el.parser.AstValue.getValue(AstValue.java:169)
    org.apache.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:190)
    org.apache.jasper.runtime.PageContextImpl.proprietaryEvaluate(PageContextImpl.java:944)
    org.apache.jsp.purchase_jsp._jspx_meth_c_005fout_005f1(purchase_jsp.java:310)
    org.apache.jsp.purchase_jsp._jspService(purchase_jsp.java:178)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:443)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:386)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:330)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    com.product.controller.ProductController.doGet(ProductController.java:57)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)

我尝试将 Rate 的输入字段类型更改为 "number"，但出现相同的错误。

由于错误显示在 value="<c:out value="${product.rate}" />" 行中，并且我在评论时没有错误，我认为我使用错误的方式使用 EL 吗？

但是下拉列表中的产品列表在我使用 EL 的地方显示正确。

有人能告诉我我做错了什么吗？

谢谢。

编辑： 乘积class如下：

public class Product {
    private int pid;
    private String name;
    private int quantity;
    private int rate;
    private int total;
    private Date date;

    public int getPid() {
        return pid;
    }
    public void setPid(int pid) {
        this.pid = pid;
    }

    public Date getDate() {
        return date;
    }
    public String getName() {
        return name;
    }
    public int getQuantity() {
        return quantity;
    }
    public int getRate() {
        return rate;
    }
    public int getTotal() {
        return total;
    }
    public void setDate(Date date) {
        this.date = date;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
    public void setRate(int rate) {
        this.rate = rate;
    }
    public void setTotal(int total) {
        this.total = total;
    }

}

Answer 1

对我来说一切都很好；您确定没有插入 'rate' 作为值吗？

尝试不使用 el 输出 rate，看看实际值是多少：

${product.rate}

创建一个javascript函数

function setRate(el) {
      document.getElementById("rate").value = el.value;
}

并将此添加到 select:

<select name="selectedProduct" onchange=setRate(this)>

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