Attribute spring form taglib disabled attribute should really be allowed for string?

Question

Recently, I played with the spring formlib tag and came across a pretty troubling phenomenon.

<form:select path="whatever" disabled="${true}"> 

Will display a select element that is NOT disabled

 <form:select path="whatever" disabled="${'true'}"> 

Will display a select element that is disabled by IS.

This tells me that the tag expects a string in this attribute and refuses to force any boolean values ​​(perhaps it checks the type first).

The effect is that I cannot do something like <form:select path="whatever" disabled="${someOtherfield.selectedId != -1}" /> , which often happens on our system.

Am I just missing some of the functionality of form taglibs? Is this a legit design decision? Defect?

Answer 1

Well, I did a few more digging around this because the detour looked too ugly.

http://forum.springsource.org/showthread.php?t=84102

The problem was that the JSP evaluated el and blindly compared the result of that evaluation using "true .equals"

Comparing String with a boolean using this method will always return false, because the type does not match, so it is definitely a defect.

Fortunately, the failure method isDisabled is protected by one liner, so I was able to get around it by expanding 8 input tags and processing this method to make a slightly more reliable comparison.

So the answer is: yes, this is a defect, and from skaffman's comments, it looks like the problem with the old library does not update very well as the JSP EL is introduced.

Thank you guys for your answers.

Answer 2

This is a little strange enough. Spring source code shows that the disabled SelectTag property is String , not boolean . This is clearly not the case, but I suspect it is for legacy reasons (spring -form.tld pre-dates JSP EL).

This leaves it at JSP runtime to force boolean to String , and apparently it will not. I am less surprised by this, as JSP EL is known to be limited.

So, you get between two dilapidated implementations. You just need to make sure that you pass String values ​​to this attribute.

Answer 3

The reason for this design is that they have a special backup code to force the definition of an EL expression when the container does not evaluate it. For example, this code:

 <%@ page isELIgnored = "true" %> ... ${'Simple text'} <spring:message text = "${'Message text'} />" 

produces ${'Simple text'} Message text

Perhaps this is useful for some weird container configurations.

That is, the following code will not work if they make the disabled boolean attribute:

 <%@ page isELIgnored = "true" %> ... <form:select ... disabled = "${true}" />