@RequestBody的理解

What you are asking for is fundamentally wrong. POST requests sends data in a body payload, which is mapped via @RequestBody. @RequestParam is used to map data through the URL parameters such as /url?start=foo. What you are trying to do is use @RequestParam to do the job of @RequestBody.

Alternative solutions for REST controllers

• Introduce a DTO class. It is the most preferred and clean method.
• If you really want to avoid creating a class, you can use @RequestBody Map<String, String> payload. Be sure to include 'Content-Type': 'application/json' in your request header.
• If you really want to use @RequestParam, use a GET request instead and send your data via URL parameters.

Alternative solutions for MVC controllers

• Introduce a DTO class and use it with annotation @ModelAttribute.
• If you transform the form data into JSON, you can use @RequestBody Map<String, String> payload. To do this, please see this answer.

It is not possible to map form data encoded data directly to a Map<String, String>.