What is <form:select path> in spring tag use

问题:

Can someone please tell me what do I need to specify in <form:select> path attribute and what it's used for? actually I need to understand how the value of the selected item from the dropdown is passed onto the controller?

回答1:

Say you have a model (Dog for example), a Dog has various attributes:
name
age
breed

if you want to make a simple form for adding/editing a dog, you'd use something that looks like this:

<form:form action="/saveDog" modelAttribute="myDog">

    <form:input path="name"></form:input>
    <form:input path="age"></form:input>
    <form:select path="breed">
        <form:options items="${allBreeds}" itemValue="breedId" itemLabel="breedName" />
    </form:select>

</form:form>

As you can see, I've chosen the breed property to be a select, because I don't want the user to type whatever breed he want, I want him to choose from a list (allBreeds in this case, which the controller will pass to the view).

In the <form:select> I've used path to tell spring that the select has to bind to the breed of the Dog model.

I've also used <form:options> to fill the select with all the options available for the breed attribute.

The <form:select> is smart, and if it's working on a populated model (i.e a Dog fetched from the database or with default breed value) - it will automatically select the "right" option from the list.

In this case, the controller will look similar to this:

@RequestMapping(value="/saveDog")
public String saveDog(@ModelAttribute("myDog") Dog dogFromForm){
    //dogFromForm.getBreed() will give you the selected breed from the <form:select
...
//do stuff
...
}

I hope my answer gave you a general idea.