You will usually see this type of error when Spring MVC finds a request mapping that matches the URL path but the parameters (or headers or something) don’t match what the handler method is expecting.

If you use the @RequestBody annotation then I believe Spring MVC is expecting to map the entire body of the POST request to an Object. I’m guessing your body is not simply a String, but some full JSON object.

If you have a java model of the JSON object you are expecting then you could replace the String parameter with that in your doSomething declaration, such as

public void doSomething(@RequestBody MyObject myobj) {

If you don’t have a Java object that matches the JSON then you could try to get it working by replacing the String type with a Map<String, Object> and see if that gets you closer to a working solution.

You could also turn on debug logging in Spring MVC to get more information on why it was a bad request.

Edit: Given your requirements in the comments, you could simply inject the HttpServletRequest into your method and read the body yourself.

public void doSomething(HttpServletRequest request) {
  String jsonBody = IOUtils.toString( request.getInputStream());
  // do stuff
}

https://stackoverflow.com/questions/16467035/spring-mvc-dont-deserialize-json-request-body