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A JSON request is an HTTP request using a valid JSON payload as request body. It must specify the text/json or application/json mime type in its Content-Type header.

By default an Action uses an any content body parser, which lets you retrieve the body as JSON (actually as a JsValue):

def sayHello = Action { request =>
  request.body.asJson.map { json =>
    (json \ "name").asOpt[String].map { name =>
      Ok("Hello " + name)
    }.getOrElse {
      BadRequest("Missing parameter [name]")
    }
  }.getOrElse {
    BadRequest("Expecting Json data")
  }
}

It's better (and simpler) to specify our own BodyParser to ask Play to parse the content body directly as JSON:

def sayHello = Action(parse.json) { request =>
  (request.body \ "name").asOpt[String].map { name =>
    Ok("Hello " + name)
  }.getOrElse {
    BadRequest("Missing parameter [name]")
  }
}

Note: When using a JSON body parser, the request.body value is directly a valid JsValue.

You can test it with cURL from the command line:

curl 
  --header "Content-type: application/json" 
  --request POST 
  --data '{"name": "Guillaume"}' 
  http://localhost:9000/sayHello

It replies with:

HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Content-Length: 15

Hello Guillaume

In our previous example we handle a JSON request, but we reply with a text/plain response. Let’s change that to send back a valid JSON HTTP response:

def sayHello = Action(parse.json) { request =>
  (request.body \ "name").asOpt[String].map { name =>
    Ok(toJson(
      Map("status" -> "OK", "message" -> ("Hello " + name))
    ))
  }.getOrElse {
    BadRequest(toJson(
      Map("status" -> "KO", "message" -> "Missing parameter [name]")
    ))
  }
}

Now it replies with:

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Content-Length: 43

{"status":"OK","message":"Hello Guillaume"}

Next: Working with XML