How to save changes data in ckeditor after submit form?

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Javascript

Java

HTML

JSP

CKEditor

I'm using JSP and CKEditor to get website's content

<form method="POST">
       <textarea id="editor" name="editor">DEMO CKEDITOR</textarea>
       <input type="submit" value="Save changes">

       <div id="content" ></div>

       <script type="text/javascript">
           CKEDITOR.replace('editor');
       </script>
</form>

The contents of webiste are saved in div "content". How can I load them into CKEditor to edit and save changes?. After submit form, the website will display new content.

What I have tried:

I think we can use Ajax. But I'm a newbie and I'm not really understand it. I'm open to any help.
Thanks in advance!