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unable to display bean property using ArrayList

Greenhorn

Posts: 7

posted 18 years ago

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Hi all,

I am new to JSP / EL.

I have a function to return an ArrayList of CategoryBean objects. When i tried to display in the JSP i get an exception.

The JSP code:
title>Welcome to Hbcdpm Store</title>
</head>
<body>

${categoryList[0].categoryId}

The Servlet code:

ArrayList<CategoryBean> results=categoryList.getCategoryName();
request.setAttribute("categoryList",results);
RequestDispatcher view = request.getRequestDispatcher("Main.jsp");
view.forward(request,response);

The exception was:

javax.servlet.ServletException: Unable to find a value for "categoryId" in object of class "au.org.hbc.main.CategoryBean" using operator "."

If i changed the JSP to display :

${categoryList[0]

then i get the output:
au.org.hbc.main.CategoryBean@9a9b65

Can someone please tell me what i have done wrong?

Thanks

Philip Tao

Greenhorn

Posts: 7

posted 18 years ago

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I forgot to include the CatalogBean code:

String getCategoryId() {
return category_id;
}

String getCategoryDescription() {
return category_description;
}

Natasza Biecek

Greenhorn

Posts: 28

posted 18 years ago

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Hi,

please, try to use JSTL <c:forEach> tag,
for example:

regards,
Natasza

Philip Tao

Greenhorn

Posts: 7

posted 18 years ago

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Hi Natasza,

I copied the code to my jsp and i get the following error:

org.apache.jasper.JasperException: /Main.jsp(19,0) According to TLD or attribute directive in tag file, attribute items does not accept any expressions

Philip Tao

Greenhorn

Posts: 7

posted 18 years ago

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Hi,

I have gone through the JSTL installation i have and fix the taglib definition in the jsp.

Now i get a different error:

type Exception report
 
message
 
description The server encountered an internal error () that prevented it from fulfilling this request.
 
exception
 
org.apache.jasper.JasperException: Exception in JSP: /Main.jsp:18
 
15: 
16: 
17: <c:forEach var='oneCatItem' items='${categoryList}'>
18:     <c:out value="${oneCatItem.categoryId}"/>
19:     <c:out value="${oneCatItem.categoryDescription}"/>
20:     <br>
21: </c:forEach>

Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:506)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
au.org.hbc.main.MainPage.doGet(MainPage.java:30)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
 
root cause
 
javax.servlet.ServletException: Unable to find a value for "categoryId" in object of class "au.org.hbc.main.CategoryBean" using operator "."
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:843)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:776)
org.apache.jsp.Main_jsp._jspService(Main_jsp.java:85)

Philip Tao

Greenhorn

Posts: 7

posted 18 years ago

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I run tomcat 5.5.

My entire jsp code:

Web.xml

My Servlet:

Philip Plenckers

Greenhorn

Posts: 18

posted 18 years ago

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Hi Philip,

it must be in our name ;) . I get exact the same error....

So, when I saw your post I hoped for an answer... but didn't find one yet. ;(

MyJSP:

<table>
<c:forEach var="location" items="${form.locations}">
<tr>
<td><c:out value="${location.locationId}"/></td>
<td><c:out value="${location.locationName}"/></td>
</tr>
</c:forEach>
</table>

result:
javax.servlet.ServletException: Unable to find a value for "locationName" in object of class "java.util.HashMap$Entry" using operator "."

and:

<td>${location.locationId}/></td>
<td>${location.locationName}/></td>

and

<td>${location["locationId"]}/></td>
<td>${location["locationName"]}/></td>

produce similar results

If I leave out the name/id thing and print ${location} I actually get the reference of the object I need (10=org.circe.web.model.Location@9b8ff9/>).I quess you get the same result. So the question is why, if we invoke another method on the bean then toString(), we get the error that the actual object can not be found?

Let me know if you found something, I will do the same

Philip.

Which produces
javax.servlet.ServletException: Unable to find a value for "locationId" in object of class "java.util.HashMap$Entry" using operator "."

Philip

Philip Plenckers

Greenhorn

Posts: 18

posted 18 years ago

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Hi Philip,

I guess in this case you have to write your own custom library tag. But as you I'm quite new to this issue.

But from p 438 of HeadFirst Servlets and JSP's I conclude that the <c:forEach> etc. is only capable of invoking the toString() method of the object in the Collection.
If this is enough you can simple override this method.
Maybe someone else can confirm this?

Philip

Philip

Natasza Biecek

Greenhorn

Posts: 28

posted 18 years ago

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Hi Philip & Philip,

Below you have my (working) vision of bean, servlet and jsp,
for ArrayList and HashMap both...

CatalogBean.java

catTestServlet.java

import java.io.*;
import java.net.*;
import java.util.ArrayList;
import javax.servlet.*;
import javax.servlet.http.*;
 
public class catTestServlet extends HttpServlet {
    
    protected void processRequest(HttpServletRequest req, HttpServletResponse res)
    throws ServletException, IOException {

// for Philip (first)
ArrayList categoryList = new ArrayList();
for (int i = 0; i < 5; i++ ) {
    categoryList.add ( new CatalogBean ( i , "descr_" + i ) );
}
req.setAttribute( "categoryList", categoryList );

// for Philip (second)
HashMap categoryMap = new HashMap();
for (int i = 100; i < 105; i++ ) {
    categoryMap.put( "key_" + i, new CatalogBean ( i , "descr_" + i ) );    
}
req.setAttribute( "categoryMap", categoryMap );

RequestDispatcher disp = req.getRequestDispatcher( "catTestPage.jsp" );
disp.forward( req, res );
    }
    
    protected void doGet( HttpServletRequest req, HttpServletResponse res )
    throws ServletException, IOException {
processRequest( req, res );
    }
    
    protected void doPost( HttpServletRequest req, HttpServletResponse res )
    throws ServletException, IOException {
processRequest( req, res );
    }
    
}

and catTestPage.jsp

Originally posted by Philip Plenckers:

MyJSP:
<table>
<c:forEach var="location" items="${form.locations}">
<tr>
<td><c:out value="${location.locationId}"/></td>
<td><c:out value="${location.locationName}"/></td>
</tr>
</c:forEach>
</table>
result:
javax.servlet.ServletException: Unable to find a value for "locationName"
in object of class "java.util.HashMap$Entry" using operator "."

Hmm.... HashMap is a collection of pairs... key + value
key identifies an entry, value - contains object...
when c:forEach iterates through collection, it extracts these pairs,
so, to access fields in your object you have to get the object first via '.value'
Please, look at the second part of processRequest() method in code above...

I need a cup of coffee...

regards,
Natasza

ps.
my current environment is: NetBeans 5.0 (bundled Tomcat 5.5.9), JDK 1.4.2, JSTL 1.1

Philip Plenckers

Greenhorn

Posts: 18

posted 18 years ago

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Hi Natasza,

absolutely great!!!

thanks a lot,

Philip (second)

Philip

Philip Tao

Greenhorn

Posts: 7

posted 18 years ago

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Hi Natasza,

Wow! Thanks for the example. It has helped me alot.

At first finding my mistakes was quite hard even though i have your working copy to compare with.

I have discovered the following problems with my code and my setup:

1. I have wrong jstl libraries in the WEB-INF/lib directory. I have a extra library standard-1.0.2.jar and also standard.jar.
2. My java bean class CategoryBean has default access instead of public access (i don't know how i didn't pick it up after checking my code so many times).

I am jumping for joy now too!!

Once again thanks for spending time answering my question.

Regards,

Philip Tao

Consider Paul's rocket mass heater.