§Handling and serving JSON requests
§Handling a JSON request
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
):
package controllers
import play.api._
import play.api.mvc._
import play.api.libs.json._
// you need this import to have combinators
import play.api.libs.functional.syntax._
object Application extends Controller {
implicit val rds = (
(__ \ 'name).read[String] and
(__ \ 'age).read[Long]
) tupled
def sayHello = Action { request =>
request.body.asJson.map { json =>
json.validate[(String, Long)].map{
case (name, age) => Ok("Hello " + name + ", you're "+age)
}.recoverTotal{
e => BadRequest("Detected error:"+ JsError.toFlatJson(e))
}
}.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.validate[(String, Long)].map{
case (name, age) => Ok("Hello " + name + ", you're "+age)
}.recoverTotal{
e => BadRequest("Detected error:"+ JsError.toFlatJson(e))
}
}
Note: When using a JSON body parser, the
request.body
value is directly a validJsValue
.
Please note:
§implicits Reads[(String, Long)]
It defines an implicits Reads using combinators which can validate and transform input JSON.
§json.validate[(String, Long)]
It explicitly validates & transforms input JSON according to implicit Reads[(String, Long)]
You can test it with cURL from the command line:
§json.validate[(String, Long)].map{ (String, Long) => ... }
This maps the result in case of success to transform it into an action result.
§json.validate[(String, Long)].recoverTotal{ e: JsError => ... }
recoverTotal
takes a function to manage errors and returns a default value:
- it ends the JsResult
modification chain and returns the successful inner value
- or if detected a failure, it returns the result of the function provided to recoverTotal
.
§JsError.toFlatJson(e)
This is a helper that transforms the JsError
into a flattened JsObject form :
JsError(List((/age,List(ValidationError(validate.error.missing-path,WrappedArray()))), (/name,List(ValidationError(validate.error.missing-path,WrappedArray())))))
would become JsValue:
{"obj.age":[{"msg":"validate.error.missing-path","args":[]}],"obj.name":[{"msg":"validate.error.missing-path","args":[]}]}
Please note a few other helpers should be provided later.
Let’s try it
§case OK
curl
--header "Content-type: application/json"
--request POST
--data '{"name": "Toto", "age": 32}'
http://localhost:9000/sayHello
It replies with:
HTTP/1.1 200 OK
Content-Type: text/plain; charset=utf-8
Content-Length: 47
Hello Toto, you're 32
§case KO “JSON missing field”
curl
--header "Content-type: application/json"
--request POST
--data '{"name2": "Toto", "age2": 32}'
http://localhost:9000/sayHello
It replies with:
HTTP/1.1 400 Bad Request
Content-Type: text/plain; charset=utf-8
Content-Length: 106
Detected error:{"obj.age":[{"msg":"validate.error.missing-path","args":[]}],"obj.name":[{"msg":"validate.error.missing-path","args":[]}]}
§case KO “JSON bad type”
curl
--header "Content-type: application/json"
--request POST
--data '{"name": "Toto", "age": "chboing"}'
http://localhost:9000/sayHello
It replies with:
HTTP/1.1 400 Bad Request
Content-Type: text/plain; charset=utf-8
Content-Length: 100
Detected error:{"obj.age":[{"msg":"validate.error.expected.jsnumber","args":[]}]}
§Serving a JSON response
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.validate[(String, Long)].map{
case (name, age) => Ok(Json.obj("status" ->"OK", "message" -> ("Hello "+name+" , you're "+age) ))
}.recoverTotal{
e => BadRequest(Json.obj("status" ->"KO", "message" -> JsError.toFlatJson(e)))
}
}
Now it replies with:
HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Content-Length: 47
{"status":"OK","message":"Hello Toto, you're 32"}
§Sending JSON directly
Sending the list of Todos with Play 2.1 and JSON is very simple:
import play.api.libs.json.Json
def tasksAsJson() = Action {
Ok(Json.toJson(Task.all().map { t=>
(t.id.toString, t.label)
} toMap))
}
Next: Working with XML