@Controller and @RestController

@Controller

1. Returning Views with Controller

• Traditional Spring MVC controller

• Mainly used to return Views

  • Returns a ViewName!

• A ViewResolver is used to render a View from the ViewName returned by the Controller

  • Finds and renders a View according to the ViewResolver configuration

2. Returning Data with Controller

• When data needs to be returned instead of a View, the @ResponseBody annotation must be used for data return

  • The @ResponseBody annotation allows a Controller to return data in JSON format!

  • The returned object is serialized to JSON and returned to the user

• When returning objects through a Controller, they are generally wrapped in ResponseEntity

  • To return objects, HttpMessageConverter operates instead of ViewResolver

  • HttpMessageConverter has several Converters registered, and the Converter used varies depending on the data to be returned

    • For strings: StringHttpMessageConverter

    • For objects: MappingJackson2HttpMessageConverter

• Spring combines the client's Http Accept header and the server's Controller return type information to select the appropriate HttpMessageConverter to process it

@RestController

• Restful web service controller

• @Controller with @ResponseBody added

  • An HTTP Response Body is generated

  • The behavior is exactly the same as attaching @ResponseBody to @Controller!

  • Allows using @ResponseBody, which was previously declared on each method, all at once

• The main purpose is to return object data in JSON format!

• Mainly used when developing REST APIs, and objects are wrapped in ResponseEntity for return