§Handling and serving JSON

§Handling a JSON request

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

By default an action uses an any content body parser, which you can use to retrieve the body as JSON (actually as a Jackson JsonNode):

import com.fasterxml.jackson.databind.JsonNode;
...

public static Result sayHello() {
  JsonNode json = request().body().asJson();
  if(json == null) {
    return badRequest("Expecting Json data");
  } else {
    String name = json.findPath("name").textValue();
    if(name == null) {
      return badRequest("Missing parameter [name]");
    } else {
      return ok("Hello " + name);
    }
  }
}

Of course it’s way better (and simpler) to specify our own BodyParser to ask Play to parse the content body directly as JSON:

import com.fasterxml.jackson.databind.JsonNode;
import play.mvc.BodyParser;
...

@BodyParser.Of(BodyParser.Json.class)
public static Result sayHello() {
  JsonNode json = request().body().asJson();
  String name = json.findPath("name").textValue();
  if(name == null) {
    return badRequest("Missing parameter [name]");
  } else {
    return ok("Hello " + name);
  }
}

Note: This way, a 400 HTTP response will be automatically returned for non JSON requests with Content-type set to application/json.

You can test it with cURL from a 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

§Serving a JSON response

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

import play.libs.Json;
import com.fasterxml.jackson.databind.JsonNode;
...

public static Result sayHello() {
  ObjectNode result = Json.newObject();
  result.put("exampleField1", "foobar");
  result.put("exampleField2", "Hello world!");
  return ok(result);
}

Now it replies with:

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

{"exampleField1":"foobar","exampleField2":"Hello world!"}

You can also return a Java object and have it automatically serialized to JSON by the Jackson library:

import play.libs.Json;
...

public Result getPeople() {
  List<Person> people = personDao.findAll();
  return ok(Json.toJson(people));
}

Next: Working with XML