问题
A few html tags interpret "any" value of a give attribute as "true" -> option tags come to mind.
I frequently end up doing something like this:
<c:choose>
<c:when test="${isSelected}"/>
<option selected="true">Opt1</option>
</c:when>
<c:otherwise/>
<option>Opt1</option>
</c:otherwise>
</c:choose>
I know I can declare a custom to encapslate this behaviour but that also gets pretty ugly, unless I code it in java.
Is there a smarter way to do this ?
回答1:
One way to approach this would be to use custom tag(s).
I like the approach that the JSP2X converter takes, defining custom tags in your WEB-INF/tags folder that let you do this:
<jspx:element name="option">
<c:if test="${selected}">
<jspx:attribute name="selected">selected</jspx:attribute>
</c:if>
<jspx:body>Opt1</jspx:body>
</jspx:element>
A more compact approach might be to create a custom tag specifically for an option that did the right thing, taking a boolean value for the selected attribute, emitting a selected="selected" attribute if it's true, not otherwise. This would be a bit more compact:
<jspx:option selected="${selected}">Opt1</option>
回答2:
Yes, a smarter way would be to write
<option selected="selected">Opt1</option>
as that's what's mandated by XHTML.
I know that's not what you're really asking :-) I think your way is fine or you can use a conditional expression instead:
<option ${isSelected?"selected=\"selected\"":""}>Opt1</option>
It's shorter though not necessarily prettier.
回答3:
For the <select><option selected="selected"> problem, I decided I wouldn't mind a bit of verboseness, if it was only one-time-verboseness... so I created a tag document (.tagx) in /WEB-INF/tags/select.tagx like so:
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="2.1"
xmlns:c="http://java.sun.com/jsp/jstl/core">
<jsp:directive.attribute name="id" required="true" />
<jsp:directive.attribute name="name" required="true" />
<jsp:directive.attribute name="options" required="true" />
<jsp:directive.attribute name="selected" required="true" />
<select id="${id}" name="${name}">
<c:forEach var="opt" items="${options}">
<c:choose>
<c:when test="${opt == selected}"><option selected="selected">${opt}</option></c:when>
<c:otherwise><option>${opt}</option></c:otherwise>
</c:choose>
</c:forEach>
</select>
</jsp:root>
and use it like so:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<html xmlns="http://www.w3.org/1999/xhtml" version="2.1"
...
xmlns:form="urn:jsptagdir:/WEB-INF/tags/">
...
<head>
...
</head>
<body>
<form method="POST" commandName="loginRequest" action="index_login.html">
<fieldset id="loginFieldSet">
...
<div>
<label for="day" path="day">Favourite day: </label>
<form:select id="day" name="day" selected="Saturday"
options="Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,Sunday" />
</div>
</fieldset>
<div>
<input type="submit" tabindex="3" />
<input type="reset" tabindex="4" />
</div>
</form>
</body>
</html>
krosenvold, I don't agree that this is ugly... maybe annoying but I'm actually glad I didn't have to write any code for this. Once you've defined the tag, your JSPXs become much tidier. Besides, I simply don't think there is a short cut for this.
回答4:
There is another way to get around this. It's a bit of a hack but an alternative to using a taglib or a choose where you duplicate the tag which I discovered works quite well.
You can build the tag inside a jstl set tag as the value, something like this:
<c:set var="mytag" value="< option ${isSelected ? 'selected='\true\' : '' } >">
Then, wherever you want that tag, you just output like this:
${mytag}
来源：https://stackoverflow.com/questions/1761479/how-to-output-option-selected-true-from-jspx