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jsp:useBean tag

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posted 24 years ago

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Hi everybody,
If I access the <jsp:useBean ...> tag for the same Bean object 5 times how many instances of that Bean are created?
eg. <jsp:useBean id="xx" scope="session" class="pac.Abean">

Nitin Dubey

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posted 24 years ago

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Hi all,
I have a problem with usebean tag in JSP. My jsp is unable to find the bean. m using tomcat and have placed the bean and jsp file in /examples/jsp.
my jsp file looks like this.....<html>
<head>
<title>
Color Demo Example
</title>
</head>
<body>


<%@ page language="java" %>
<%! char c = 0; %>
<jsp:useBean id="letterColor" scope="application" class="AlphabetCode" />
<%
for(int i=0;i<26;i++){
for(int j=0;j<26;j++){
c=(char)(0x41+(26-i+j)%26);
Character thisChar=new Character(c);
letterColor.setCharacter(thisChar.toString());
%>
<font color=<%=letterColor.getColor() %> >
<%=letterColor.getCharacter() %>
</font>
<%
}
%>
<br>
<%
}
%>
</body>
</html>
let me know where i have gone wrong.
nitin

amit sanghai

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Posts: 231

posted 24 years ago

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Hi Nitin,
I think u should place the page directive tag at the very beginning of ur file.

Can somebody please give the answer to my question?

Peter den Haan

author

Posts: 3252

posted 24 years ago

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Originally posted by amit sanghai:

Hi everybody,
If I access the <jsp:useBean ...> tag for the same Bean object 5 times how many instances of that Bean are created?

jsp:useBean first attempts to locate the bean, and instantiates it only if it isn't found in the specified scope (see 2.13.1 of the JSP 1.1 spec). This is an absolute necessity for request- session- and application-scoped beans, otherwise they couldn't be referenced in multiple pages.
I'm not sure if you are allowed to use the same useBean more than once in a single page. The specification says, apparently unconditionally, that useBean will define "a scripting language variable with the given id in the current lexical scope of the scripting language". That could mean that two useBeans with the same id within the same lexical scope (read more or less: statement block) fail with a compilation error.
Did you try?
- Peter

Peter den Haan | peterdenhaan.com | quantum computing specialist, Objectivity Ltd

Peter den Haan

author

Posts: 3252

posted 24 years ago

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Originally posted by Nitin Dubey:
My jsp is unable to find the bean.

"My JSP generates an error. Can someone wade through a hundred lines of unformatted code and tell me what the problem is?"
Sure Nitin, but, erm, what about quoting the error message you got? They usually tell you what the error exactly is.
From your description however I'm willing to bet it's a ClassNotFound error or similar. Your bean .class file needs to go into WEB-INF/classes, not in the same directory as the .jsp.
HTH
- Peter

[This message has been edited by Peter den Haan (edited January 22, 2001).]

Peter den Haan | peterdenhaan.com | quantum computing specialist, Objectivity Ltd

amit sanghai

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posted 24 years ago

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Hi Peter,
I tried using the same jsp:useBean tag wiht the same id and class names. It is giving a fatal error : missing resource in java.util.PropertyResourceBundle.

Thanks,
Bye.

Mohd. Yakub

Greenhorn

Posts: 18

posted 19 years ago

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Originally posted by amit sanghai:

Hi everybody,
If I access the <jsp:useBean ...> tag for the same Bean object 5 times how many instances of that Bean are created?

eg. <jsp:useBean id="xx" scope="session" class="pac.Abean">

it gives error,"duplicate local variable xx.
creating a bean is conditional,means it looks for
if(xx==null){
// create new one
xx= new pac.Abean();
}
if it is already there it won't create any other
Add to this,if we decleare the bean with the same id in other page,we can
access the values set in it.
hope ur question is answered..

Yakub