Java developers- Working with JSON

Handling a JSON request

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

By default, an action uses any content body parser, which you can utilize to get the body as JSON :

public Result sayHello(Http.Request request) {
  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);
    }
  }
}
public Result sayHello(Http.Request request) {
  Optional<Person> person = request.body().parseJson(Person.class);
  return person.map(p -> ok("Hello, " + p.firstName)).orElse(badRequest("Expecting Json data"));
}

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Of course, it is a  way simpler and better to specify our BodyParser to request Play to parse the content body directly as JSON:

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

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You can test it with the help of curl from a CLI:

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

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It replies with:

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


Hello Guillaume

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Serving a JSON response

We handled a JSON request in the previous example but replied with a plain/text response. Let us change that to send back a valid JSON HTTP response:

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

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Now it replies with:

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


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

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

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

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Must Read Array of Objects in Java

Frequently Asked Questions

What is JSON used for in Java?

JSON (JavaScript Object Notation) is a  text-based, lightweight, language-independent data exchange format that is easy for machines and humans to read and write. JSON can represent two structured types: arrays and objects.

How is JSON different from JavaScript?

The last significant difference between JSON and JavaScript objects is their presentation. JSON is presented in a string. These are referred to as JSON strings. JavaScript objects can contain strings, but they are, as their name suggests, objects instead of strings.

Why do we need JSON?

The JSON format transmits and serializes structured data over network connections. It is primarily utilized to transmit data between a server and web applications. Web services and APIs use JSON format to provide public data. We can use it with modern programming languages.

Conclusion

I hope this article gave you insights into working with JSON for java developers.

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