How do I make the default response Content-type: application/json with Scalatra - scala

Question

I'm learning Scalatra and am wondering how I can make the default Content-Type of my responses application/json. The current default appears to be text/html. Neat, but not really useful to my application.
The current default is text/html.
$ curl -i -X GET 'http://localhost:8080/v1/example'
HTTP/1.1 200 OK
Date: Fri, 19 Apr 2019 07:21:21 GMT
Content-Type: text/html;charset=utf-8
Content-Length: 23
Server: Jetty(9.4.8.v20171121)
HelloWorld(hello,world)
I can get application-json explicitly through the Accepted: application/json header.
$ curl -i -X GET 'http://localhost:8080/v1/example' -H 'Accept: application/json'
HTTP/1.1 200 OK
Date: Fri, 19 Apr 2019 07:22:09 GMT
Content-Type: application/json;charset=utf-8
Transfer-Encoding: chunked
Server: Jetty(9.4.8.v20171121)
{"hello":"hello","world":"world"}
How do I set the default to be application/json.

Answer 1

defaultFormat could be overridden to make application/json the default case. For example,
import java.io.File
import org.scalatra._
import org.scalatra.util.MimeTypes
import org.json4s.{DefaultFormats, Formats}
import org.scalatra.json._
case class HelloWorld(hello: String, world: String)
class MyScalatraServlet extends ScalatraServlet with JacksonJsonSupport {
protected implicit lazy val jsonFormats: Formats = DefaultFormats
override def defaultFormat: Symbol = 'json
get("/v1/example") {
HelloWorld("hello", "world")
}
}
without specifying Accept header should respond with
curl -i -X GET 'http://localhost:8080/v1/example'
HTTP/1.1 200 OK
Date: Thu, 25 Apr 2019 22:28:37 GMT
Content-Type: application/json;charset=utf-8
Content-Length: 33
Server: Jetty(9.4.8.v20171121)
{"hello":"hello","world":"world"}
whilst explicitly requesting Accept: text/html also works
curl -i -X GET 'http://localhost:8080/v1/example' -H 'Accept: text/html'
HTTP/1.1 200 OK
Date: Fri, 26 Apr 2019 15:45:22 GMT
Content-Type: text/html;charset=utf-8
Content-Length: 23
Server: Jetty(9.4.8.v20171121)
HelloWorld(hello,world)