February 2005
Intermediate to advanced
528 pages
12h 53m
English
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3.12. Handling Unchecked Checkboxes
Problem
You need to ensure that a Boolean ActionForm
property, corresponding to an HTML checkbox, is set to
false when the checkbox is unchecked.
Solution
Create a checkbox input field that uses JavaScript to set the value
of a hidden Boolean field. Use the logic:equal tag
to set the checked property of the checkbox if the
value for the hidden field is true. The
JSP page (checkbox_test.jsp) in Example 3-18 uses this approach to guarantee a true or
false value is always submitted.
Example 3-18. Guaranteeing checkbox settings
<%@ page contentType="text/html;charset=UTF-8"
language="java" %>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-html"
prefix="html" %>
<%@ taglib uri="http://jakarta.apache.org/struts/tags-logic"
prefix="logic" %>
<html>
<head>
<title>Struts Cookbook - Chapter 4 : Checkbox Test</title>
</head>
<body>
<html:form method="get" action="/ProcessCheckbox">
<input type="checkbox" name="foo_"
onclick="javascript:elements['foo'].value=this.checked;"
<logic:equal name="CheckboxForm" property="foo" value="true">
checked
</logic:equal>
>
<html:hidden property="foo"/>
<html:submit/>
</html:form>
</body>
</html>Discussion
For such a common little field, the HTML checkbox can cause trouble. If a checkbox is unchecked and the form is submitted, no value for that field will be sent in the request. Suppose you have a form with one checkbox on it:
<html:form method="get" action="ProcessFoo"> <html:checkbox property="foo"/> <html:submit/> </html:form> ...
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