Can we send an Object as the response of Controller handler method?

Yes, you can send an object as the response of a controller handler method in Spring MVC. This is typically done using the @ResponseBody annotation on the handler method. The @ResponseBody annotation tells Spring that the return type should be written directly to the HTTP response body, and not placed in a Model, or interpreted as a view name.

When you use @ResponseBody, Spring uses HTTP Message Converters to convert the return value to HTTP response body, based on the content-type in the request HTTP header. Commonly, this involves converting the return object to JSON or XML format.

For example, if you have a controller method that returns an instance of a User class, you can annotate this method with @ResponseBody, and Spring will automatically serialize the User object into JSON format and write it to the response body:

@RequestMapping(value = "/user", method = RequestMethod.GET)
@ResponseBody
public User getUser() {
    return new User("John", "Doe");
}

In this example, when the /user endpoint is accessed, it will return a JSON representation of the User object. The actual conversion from the User object to JSON is typically handled by the MappingJackson2HttpMessageConverter if Jackson is on the classpath[2][9].

Additionally, if you are using Spring 4.1 and above, you can also use the ResponseEntity object to return the response. ResponseEntity allows more flexibility as it can contain both the body and the status code, making it useful for finer control over the response details:

@RequestMapping(value = "/user", method = RequestMethod.GET)
public ResponseEntity<User> getUser() {
    User user = new User("John", "Doe");
...