@RequestBody and @ResponseBody annotations in Spring

There is a whole Section in the docs called 16.3.3.4 Mapping the request body with the @RequestBody annotation. And one called 16.3.3.5 Mapping the response body with the @ResponseBody annotation. I suggest you consult those sections. Also relevant: @RequestBody javadocs, @ResponseBody javadocs

Usage examples would be something like this:

Using a JavaScript-library like JQuery, you would post a JSON-Object like this:

{ "firstName" : "Elmer", "lastName" : "Fudd" }

Your controller method would look like this:

// controller
@ResponseBody @RequestMapping("/description")
public Description getDescription(@RequestBody UserStats stats){
    return new Description(stats.getFirstName() + " " + stats.getLastname() + " hates wacky wabbits");
}

// domain / value objects
public class UserStats{
    private String firstName;
    private String lastName;
    // + getters, setters
}
public class Description{
    private String description;
    // + getters, setters, constructor
}

Now if you have Jackson on your classpath (and have an <mvc:annotation-driven> setup), Spring would convert the incoming JSON to a UserStats object from the post body (because you added the @RequestBody annotation) and it would serialize the returned object to JSON (because you added the @ResponseBody annotation). So the Browser / Client would see this JSON result:

{ "description" : "Elmer Fudd hates wacky wabbits" }

See this previous answer of mine for a complete working example: https://stackoverflow.com/a/5908632/342852

Note: RequestBody / ResponseBody is of course not limited to JSON, both can handle multiple formats, including plain text and XML, but JSON is probably the most used format.

Update

Ever since Spring 4.x, you usually won’t use @ResponseBody on method level, but rather @RestController on class level, with the same effect.

Here is a quote from the official Spring MVC documentation:

@RestController is a composed annotation that is itself meta-annotated
with @Controller and @ResponseBody to indicate a controller whose
every method inherits the type-level @ResponseBody annotation and,
therefore, writes directly to the response body versus view resolution
and rendering with an HTML template.