Example of using Circe with java.net.http

http-demo.sc

#!/usr/bin/env -S scala
// Brian Schlining. 2024-12-22

//> using dep "io.circe::circe-core:0.14.10"
//> using dep "io.circe::circe-generic:0.14.10"
//> using dep "io.circe::circe-parser:0.14.10"

import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
import io.circe.parser.decode

import java.net.URI
import java.net.http.{HttpClient, HttpRequest, HttpResponse}
import java.nio.charset.StandardCharsets

// --- JSON Decoding ---

// Circe uses case classes to represent JSON objects
final case class Names(items: List[String], limit: Int, offset: Int, total: Int)

// Circe can automatically derive a Decoder for a case class
given Decoder[Names] = deriveDecoder[Names]

// This is a custom BodyHandler that uses Circe to decode the response body.
// It can decode any type T for which there is an implicit Decoder[T] in scope.
class CirceBodyHandler[T: Decoder] extends HttpResponse.BodyHandler[Either[Throwable, T]]:

    override def apply(responseInfo: HttpResponse.ResponseInfo): HttpResponse.BodySubscriber[Either[Throwable, T]] =
        HttpResponse
            .BodySubscribers
            .mapping(HttpResponse.BodySubscribers.ofString(StandardCharsets.UTF_8), s => decode[T](s))

// Factory method for creating a CirceBodyHandler. This isn't strictly necessary,
// but it follows the java.net.http.HttpResponse.BodyHandlers factory method styles
object CirceBodyHandler:

    def of[T: Decoder]: CirceBodyHandler[T] = new CirceBodyHandler[T]()

// -- Using the CirceBodyHandler with HttpClient --
val uri = URI.create("https://database.fathomnet.org/worms/names")

val client = HttpClient.newHttpClient();

val request = HttpRequest
            .newBuilder()
            .uri(uri)
            .header("Accept", "application/json")
            .GET()
            .build()

val response = client.send(request, CirceBodyHandler.of[Names])

response.body() match
    case Left(e) => println(s"Failed to parse response: $e")
    case Right(names) => println(s"Names: $names")