checkBox
Purpose
Creates a checkbox form field. All the usual HTML elements apply.
Examples
<g:checkBox name="myCheckbox" value="${true}" />Description
Attributes
name - The name of the checkbox 
value (optional) - The value of the checkbox 
checked (optional) - Expression if evaluates to true sets to checkbox to checked 
The checkBox tag typically only requires the name and value attributes and will infer whether the checkbox should be checked or not from the value. However, if you need to override this behaviour the checked attribute can be used for fine grained control.Source
Show Source
def checkBox = { attrs ->
        attrs.id = attrs.id ?: attrs.name
        def value = attrs.remove('value')
        def name = attrs.remove('name')
        def disabled = attrs.remove('disabled')
        if (disabled && Boolean.valueOf(disabled)) {
            attrs.disabled = 'disabled'
        }        // Deal with the "checked" attribute. If it doesn't exist, we
        // default to a value of "true", otherwise we use Groovy Truth
        // to determine whether the HTML attribute should be displayed or not.
        def checked = true
        def checkedAttributeWasSpecified = false
        if (attrs.containsKey('checked')) {
            checkedAttributeWasSpecified = true
            checked = attrs.remove('checked')
        }        if (checked instanceof String) checked = Boolean.valueOf(checked)        if (value == null) value = false        out << "<input type=\"hidden\" name=\"_${name}\" /><input type=\"checkbox\" name=\"${name}\" "        if (checkedAttributeWasSpecified) {
            if (checked) {
                out << 'checked="checked" '
            }
        }
        else if (value) {
            out << 'checked="checked" '
        }        def outputValue = !(value instanceof Boolean || value?.class == boolean.class)
        if (outputValue) {
            out << "value=\"${value}\" "
        }
        // process remaining attributes
        outputAttributes(attrs)        // close the tag, with no body
        out << ' />'
    }