Question

我有以下java和jsp。我得到“org.apache.jasper.JasperException：在第41行处理JSP页面/Purchase.jsp时发生异常”，即：“cart.processRequest（request）;”。好吗？

<!-- ShowSession.jsp -->
<%@page import="java.util.Vector"%>
<html>    
<head>
    <title>Shopping cart example</title>
</head>

<body bgcolor="#ffffcc">

<center>
<form type="post" action="Purchase.jsp">
    <h1>Shopping cart example</h1>
    </br>Please select a product and add it to your shopping cart</br>
    <select name='product'>
        <option>Beginning java 2 by Ivor Horton</option>
        <option>Professional java programming by Brett Sell</option>
        <option selected="selected">test</option>
        <option>Professional jini by Sing Li</option>
        <option>Professional JSP by Sing Li et all</option>
        <option>Professional XLS by Andrew Watt et all</option>
        <option>XML applications by frank Boumphrey et al</option>
        <option>Beginning XML by Nikola Ozu et al</option>
        <option>Instant UML by Pierra-Alain Muller</option>
        <option>Beginning java objects by Jacquie Barker</option>
    </select>
    <input type="submit" name="submit" value="add">
</form>
<!-- Here goes the shopping cart display -->

<%  String submit = request.getParameter("submit");
    if(submit != null)
    {
%>

<hr><h2 align="center">Your shopping cart</h2><p>

<jsp:useBean id="cart" scope="session" class="utilities.ShoppingCart" />
<jsp:setProperty name="cart" property="*" />

<%  cart.processRequest(request); %>

<table width="75%" align="center" border="1">

<%  Vector products = cart.getProducts();
    for(int i=0; i<products.size(); i++)
    {
%>

<tr bgcolor="#F9AD00">
    <td><%=products.get(i) %></td>
    <td><a href="Purchase.jsp?product=<%=products.get(i) %>&submit=remove">Remove</a></td>
</tr>

<%  }
    if(products.size() == 0)
    {
%>

<tr>
    <td>Your cart is currently empty</td>
</tr>

<%  } %>

</table>

<%  } %>

</center>

</body>
</html>

＆lt; = - jsp和java - =＆gt;

package utilities;

import java.util.Vector;
import javax.servlet.http.HttpServletRequest;

public class ShoppingCart extends Object
{
    private Vector<String> cart = null;
    String product = null;
    String submit = null;

    public ShoppingCart() { }

    public ShoppingCart(String product)
    {
        cart = new Vector<String>();
    }

    public void setProduct(String product)
    {
        this.product = product;
    }

    public void setSubmit(String submit)
    {
        this.submit = submit;
    }

    public Vector getProducts()
    {
        return cart;
    }

    public void addProduct(String product)
    {
        cart.add(product);
    }

    public void removeProduct(String product)
    {
        cart.remove(product);
    }

    public void processRequest(HttpServletRequest reg)
    {
        if(submit != null)
            if(submit.equals("add"))
                addProduct(product);
            else
                removeProduct(product);

        reset();
    }

    public void reset()
    {
        submit = null;
        product = null;
    }
}

它给了我

org.apache.jasper.JasperException: An exception occurred processing JSP page /Purchase.jsp at line 41

Answer 1

JSP useBean调用该类的无参数构造函数。您只在第二个构造函数中初始化cart（具有参数：

）

public ShoppingCart(String product)
{
    cart = new Vector<String>();
}

这个构造函数永远不会被调用。

您需要在无参数构造函数中初始化它，然后让第二个构造函数调用this()。

或者只是在声明中初始化cart：

private Vector<String> cart = new Vector<String>();

并将其从构造函数中删除。

让购物车未初始化会导致NullPointerException或addProduct中的deleteProduct。

jsp：setProperty request HttpServletRequest处理JSP页面/Purchase.jsp时发生异常

1 个答案: