[JAVA] Using hidden type when PUT with Thymeleaf

When PUT with Thymeleaf, PUT is not simply specified in the action of the form method.

Background of investigation

I implemented it so that it can be PUT, but when I was looking at the Request Method in the developer console of chrome, it turned out to be POST? Because it became. ..

Looking at From Data, it is put.

See how the Thymeleaf source is deployed

After specifying post for the action of the form tag, you can see from the source that put is realized by using the hidden type. ・ What is hidden type? https://developer.mozilla.org/ja/docs/Web/HTML/Element/Input/hidden It is used when you want to send a value without displaying it on the form.

--Thymeleaf code

`sample.html`


<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
  <head>
    <meta http-equiv='Content-type' content='text/html; charset=utf-8' />
    <title>test</title>
  </head>
  <body>
<!--Pay attention here-->
    <form th:action="@{/user}" th:method="put">
      <input class="btn btn-default btn-xs" type="submit" value="update" />
    </form>
<!--Pay attention here-->
  </body>
</html>

--Source code displayed on the screen (after thymeleaf expansion)

`sample.html`


<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv='Content-type' content='text/html; charset=utf-8' />
    <title>test</title>
  </head>
  <body>
<!--Pay attention here-->
    <form action="/user" method="post">
      <input type="hidden" name="_method" value="put"/>
      <input class="btn btn-default btn-xs" type="submit" value="update" />
    </form>
<!--Pay attention here-->
  </body>
</html>

Reason

The form tag only supports the get and post methods. Therefore, it seems that the method is to specify method =" post " on the form tag and specify value =" put " in the hidden type. As a result, Request Method is POST, but it is sent by PUT because it is sent by the method specified by _method. When I looked it up, it seems that other frameworks such as Rails also realize put in this way.