Re: JSP:Setproperty and empty strings

Hans Bergsten Fri, 13 Jun 2003 12:53:37 -0700

Tim Davidson wrote:

Thanks for your answer but this doesnt work! The following lines have no affect on the 
bean:
        <jsp:setProperty name="myBean" property="firstName" value="<%=null%>"/>
        <jsp:setProperty name="myBean" property="firstName" value="<%=""%>"/>


Which container are you using? I've tested this with Tomcat 4.1.24 and
it works as it should; the Java expression value is used as-is to set
the property to null or an empty string.

<jsp:setProperty name="myBean" property="firstName" value=""/>


A "value" attribute with a static empty string means the property setter
method isn't called; this is according to the spec. But with a Java
expression, as above, it should work (and does in TC 4.1.24).

Also:
        <jsp:setProperty name="myBean" property="*" value=""/>
or
        <jsp:setProperty name="myBean" property="*" value="<%=""%>"/>
causes:
        org.apache.jasper.JasperException: jsp.error.setProperty.invalid


Right. As someone else pointed out, you're not allowed to mix the "*"
syntax with the "value" attribute.

Any other ideas?


Some ideas have already been provided by others, such as removing the
bean and create a new one that gets populated with the current values,
or to define a "reset" property with a setter method that resets all
other property values to their defaults:

    <jsp:useBean id="myBean" scope="session" class="..." />
    <jsp:setProperty name="myBean" property="reset" value="whatever" />
    <jsp:setProperty name="myBean" property="*" />

But as you describe in another reply, when you only want to reset a
subset of the properties it's not a nice solution, since view logic
creeps into the model. In this case, resetting all properties that
correspond to text fields with a Java expression may be better:

    <jsp:useBean id="myBean" scope="session" class="..." />
    <jsp:setProperty name="myBean" property="firstName"
      value="<%= null %>" />
    <jsp:setProperty name="myBean" property="*" />

or if you use JSTL:

    <jsp:useBean id="myBean" scope="session" class="..." />
    <c:set target="myBean" property="firstName" value="" />
    <jsp:setProperty name="myBean" property="*" />

The best approach for a complex case like this is probably not to
use <jsp:setProperty> at all; use an MVC architecture (maybe using
Struts) to let a servlet (or Action class) process the request and
forward to JSP pages just for rendering the response.

Hans

-----Original Message-----
From: Hans Bergsten [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 12, 2003 5:25 PM
To: [EMAIL PROTECTED]
Subject: Re: JSP:Setproperty and empty strings

Tim Davidson wrote:

yeah, the spec is unclear on this point. I have tried this and it doesnt have the 
desired behaviour:
<jsp:SetProperty name="RequestParmBean" property="inputfieldA" value=""/>
This will not set inputfieldA to an empty string.
Does anyone know why they implemented it in this way?

I think it was for consistency with the auto-population model, i.e.,
when using property="*". But, the result is very confusing, I agree.

This should work, though, since a request-time attribute value is
used as-is:

   <jsp:setProperty name="RequestParmBean" property="inputfieldA"
     value='<%= "" ' />

or to set it to null:

   <jsp:setProperty name="RequestParmBean" property="inputfieldA"
     value='<%= null ' />

Messy ... An alternative is to use JSTL's <c:set>:

   <c:set target="${RequestParmBean}" property="inputfieldA"
     value="" />

Hans

-----Original Message-----
From: Zerbe John W [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 12, 2003 4:48 PM
To: [EMAIL PROTECTED]
Subject: Re: JSP:Setproperty and empty strings

If I am reading the spec correctly, you can initialize all of your properties individually prior to setting them from the request params. I believe that the line you quoted from the spec only applies when setting properties from request params.

eg:
<jsp:SetProperty name="RequestParmBean" property="inputfieldA" value=""/>
<jsp:SetProperty name="RequestParmBean" property="inputfieldA" param="inputfieldA"/>

or, assuming an input form the "inputfieldA" and "inputfieldB":
<jsp:SetProperty name="RequestParmBean" property="inputfieldA" value=""/>
<jsp:SetProperty name="RequestParmBean" property="inputfieldB" value=""/>
<jsp:SetProperty name="RequestParmBean" property="*"/>


-----Original Message-----
From: Tim Davidson [mailto:[EMAIL PROTECTED]
Sent: Thursday, June 12, 2003 9:30 AM
To: [EMAIL PROTECTED]
Subject: JSP:Setproperty and empty strings

Hi

Using <jsp:setProperty...> is is possbible to set empty strings? and if so how?

I realise the spec says:
 "If the parameter has an empty or null value, the corresponding Bean property is not set. 
"

but can anyone reccommend a fix?

thanks in advance.

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