Spring-mvc + Thymeleaf: dealing with complex form

I'm working on an internal tool using spring-mvc and thymeleaf.

A section of this tool is used to create an entity we save in the database. This entity is quite complex; it contains many properties and relations. Some of these relations contain list and other properties.

I have 2 constraints:

1. Single page. No "wizard".


2. To only save a completed object in the database.

Now, I'm not really asking for a specific issue. I know my way around thymeleaf, spring @ModelAttribute, etc.

My question is mostly which strategy are you choosing or how to deal with really complex object creation.

Now I can see 3 ways to do it :

1. 
   

   Rendering page with thymeleaf. Every time a new element need to be added to a list, I use Ajax to add the new element on the server and rerender the specific fragment. So doing back and forth to the server with my @ModelAttribute and only save at the end.

   
   


2. 
   

   Rendering a basic page with thymeleaf. Using JavaScript to create html elements and instead of submitting to a @ModelAttribute, I'm serializing my form to JSON and submit this JSON to the server. (kind of client side model)

   
   


3. 
   

   Rendering a basic page with thymeleaf. Create the html element dynamically with JavaScript when I need to add list item (being sure I'm putting proper name="" to fit with my Java form object) and submit the whole thing at the end.

   
   

I'm personally unsure between 1 or 2. I feel dealing with complex object is much more easier using JSON than form submission. Also, the input value/field with sub object and property can be quite nasty. Having this kind of syntax does not sound great to me...

3 can probably work but the way spring data binding is done with sub property is lacking some detail in my humble opinion (section 7.4.1 - http://ift.tt/1ngX0vf).

What do you think ?