Checkbox values do not bind into object when false?

问题

I used ModelAttribute to bind object in Spring web application.

Once I notice that, in case an object has an boolean value A is true, its value will not be updated if we uncheck A's checkbox.

For example, I have a Lesson object which has the attribute "active" = true. In "Edit Lesson" view, I make a checkbox which bind into "active". Things work well if the checkbox is checked (the binding object reflect the changes), but the object lesson will not change if we un-check the checkbox.

Further study tells me that's because the checkbox value may not get submitted by browser (this is an in-design of HTML). So I have to use the ugly request.getParameter to check if the value is set.

I just come by this question, and I see that asp.net mvc provide a way to work around it more elegantly. I think Spring must provide something similarly. Does anyone know how to do that?

Following is my code:

Controller code:

    @RequestMapping(value="/test", method = RequestMethod.POST)
    public String processEditLesson(@Valid Lesson lesson, BindingResult bindingResult, Model model) {
        System.out.println("Lesson is active: " + lesson.isActive()); // still "true" even if the checkbox is unset

        // Current work-around
        String isActive = request.getParameter("active");
        if (StringUtils.isNotNullOrEmpty(isActive)) {
            lesson.setActive(true);
        } else {
            lesson.setActive(false);
        }
        ...
    }

View code:

<form id="lesson" class="EditorForm" action="${rc.getContextUrl('/test.html')}" method="post" >

    <fieldset>
        <legend><@spring.message code="lesson.edit"/></legend>
        <@spring.formHiddenInput "lesson.id" />
        <@spring.formHiddenInput "lesson.studio.id" />

        <div class="Entry">
            <label for="name"><@spring.message code="lesson.message"/></label>
            <@spring.formInput "lesson.message" />
            <span class="ErrorMessage"><@spring.showErrors "<br/>" /></span>
        </div>

        <input type="checkbox" name="active" checked="checked" />
        <label for="active">${rc.getMessage('lesson.active')}</label>

        <input type="submit" value="<@spring.message code='common.update' />" />
    </fieldset>
</form>

回答1:

Spring has a built in workaround.

Simply add this additional hidden field to the form:

<input type="hidden" value="on" name="_active"/>

The parameter with a leading underscore is some kind of marker, to indicate the existence of a checkbox parameter with the same name, but without the underscore.

Spring should now set lesson.active to false if only _active=on is submitted.

回答2:

I think that you should use springframework tags - why are you using plain html? If your view is JSP page just import:

<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>

and then you can use:

<form:checkbox path="path" label="label" />

which handles the problem.

回答3:

You can use spring framework tags like it will automatically set you selected value to bean class and then it will be very easy to get its value in your controller class.

on path you need to put your bean variable name

and to use this you need to give command name to your form and use that command name to bind your bean object to that jsp

model.addAttribute("command name" , bean object) use this in your controller to bind object.

来源：https://stackoverflow.com/questions/8723765/checkbox-values-do-not-bind-into-object-when-false

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java