jsp:setProperty request HttpServletRequest An exception occurred processing JSP page /Purchase.jsp_问答_开发者

jsp:setProperty request HttpServletRequest An exception occurred processing JSP page /Purchase.jsp

开发者 https://www.devze.com 2023-03-01 17:45 出处：网络

I have the following java and jsp. I get \"org.apache.jasper.JasperException: An exception occurred processing JSP page /Purchase.jsp at line 41\", that is the line with :\"cart.processRequest(request

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I have the following java and jsp. I get "org.apache.jasper.JasperException: An exception occurred processing JSP page /Purchase.jsp at line 41", that is the line with :"cart.processRequest(request);". Any idea please?

<!-- 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>

<=- jsp and java -=>

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()
 开发者_如何学C   {
        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;
    }
}

It gives me

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

JSP useBean calls the no-argument constructor of the class. You only initialize cart in the second constructor (that has an argument:

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

This constructor never gets called.

You need to initialize it in the no-argument constructor and then have the second constructor call this().

Or else just initialize cart in the declaration:

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

and leave it out of the constructor.

Leaving cart uninitialized causes a NullPointerException in either addProduct or deleteProduct.

jsp:setProperty request HttpServletRequest An exception occurred processing JSP page /Purchase.jsp

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