Daikon Gson

Project

https://github.com/DaikonWeb/daikon-gson

Methods

Daikon Gson adds one method to the Response and one to the Request in order to integrate easily the JSON functionality.

Request

.json<MyClass>(): to deserialize a JSON string to the desired class instance

Response

.json(myInstance): to serialize a class instance to a JSON string

How to use

1. Define a data class

   data class Greeting(val say: String, val language: String)
   

2. Create a server and use the data class to read and produce JSON

   @Test
   fun test() {
    HttpServer()
        .post("/hello") { req, res -> res.json(req.json<Greeting>()) }
        .start().use {
            val response = "http://localhost:4545/hello".http.post(body = """{"say":"ciao","language":"ITA"}""")
            assertThat(response.body).isEqualTo("""{"say":"ciao","language":"ITA"}""")
            assertThat(response.header("Content-Type")).isEqualTo("application/json;charset=utf-8")
        }
   }
   

How to deserialize Complex Types

To deserialize and serialize a complex type, for example a LocalDate, you can define a deserializer and a serializer in this way:

Deserializer

You can deserialize a json request:

1. Define a data class

   data class Appointment(val message: String, val date: LocalDate)
   

2. Create an HttpServer

   @Test
   fun `custom deserializer`() {
    HttpServer()
        .post("/remindme") { req, res ->
            val dateDeserializer = Deserializer(LocalDate::class) { json: JsonElement, _, _ -> parse(json.asString) }
            val app = req.json<Appointment>(dateDeserializer)
            res.write("""I will remind you to "${app.message}" at ${app.date.format(ofPattern("yyyy-MM-dd"))}""")
        }
        .start().use {
            val response = "http://localhost:4545/remindme".http.post(body = """{"message":"Eat a Daikon","date":"2020-01-31"}""")
            assertThat(response.body).isEqualTo("""I will remind you to "Eat a Daikon" at 2020-01-31""")
        }
   }
   

Serializer

You can serialize a response to json:

1. Define a data class

   data class Appointment(val message: String, val date: LocalDate)
   

2. Create an HttpServer

   @Test
   fun `custom serializer`() {
    HttpServer()
        .get("/nextAppointment") { _, response ->
            val dateSerializer = Serializer(LocalDate::class) { date: LocalDate, _, _ -> JsonPrimitive(date.format(ofPattern("dd/MM/yyyy"))) }
            val app = Appointment("Eat a Daikon", parse("2020-01-31"))
            response.json(app, dateSerializer)
        }
        .start().use {
            val response = "http://localhost:4545/nextAppointment".http.get()
            assertThat(response.body).isEqualTo("""{"message":"Eat a Daikon","date":"31/01/2020"}""")
        }
   }
   

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