HTTP Request in Kotlin

Question

I'm completely new to Kotlin. I want to do a login validation using POST method and to get some information using GET method. I've URL, server Username and Password already of my previous project. I didn't find any proper example project which uses this thing. Anyone please suggest me any working example where I can use GET and POST method in HTTP request

Answer 1

import java.io.IOException
import java.net.URL

fun main(vararg args: String) {
    val response = try {
        URL("http://seznam.cz")
                .openStream()
                .bufferedReader()
                .use { it.readText() }
    } catch (e: IOException) {
        "Error with ${e.message}."
    }
    println(response)
}

Answer 2

I think using okhttp is the easiest solution. Here you can see an example for POST method, sending a json, and with auth.

val url = "https://example.com/endpoint"

val client = OkHttpClient()

val JSON = MediaType.get("application/json; charset=utf-8")
val body = RequestBody.create(JSON, "{\"data\":\"$data\"}")
val request = Request.Builder()
        .addHeader("Authorization", "Bearer $token")
        .url(url)
        .post(body)
        .build()

val  response = client . newCall (request).execute()

println(response.request())
println(response.body()!!.string())

Remember to add this dependency to your project https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp

UPDATE: July 7th, 2019 I'm gonna give two examples using latest Kotlin (1.3.41), OkHttp (4.0.0) and Jackson (2.9.9).

Get Method

fun get() {
    val client = OkHttpClient()
    val url = URL("https://reqres.in/api/users?page=2")

    val request = Request.Builder()
            .url(url)
            .get()
            .build()

    val response = client.newCall(request).execute()

    val responseBody = response.body!!.string()

    //Response
    println("Response Body: " + responseBody)

    //we could use jackson if we got a JSON
    val mapperAll = ObjectMapper()
    val objData = mapperAll.readTree(responseBody)

    objData.get("data").forEachIndexed { index, jsonNode ->
        println("$index $jsonNode")
    }
}

POST Method

fun post() {
    val client = OkHttpClient()
    val url = URL("https://reqres.in/api/users")

    //just a string
    var jsonString = "{\"name\": \"Rolando\", \"job\": \"Fakeador\"}"

    //or using jackson
    val mapperAll = ObjectMapper()
    val jacksonObj = mapperAll.createObjectNode()
    jacksonObj.put("name", "Rolando")
    jacksonObj.put("job", "Fakeador")
    val jacksonString = jacksonObj.toString()

    val mediaType = "application/json; charset=utf-8".toMediaType()
    val body = jacksonString.toRequestBody(mediaType)

    val request = Request.Builder()
            .url(url)
            .post(body)
            .build()

    val response = client.newCall(request).execute()

    val responseBody = response.body!!.string()

    //Response
    println("Response Body: " + responseBody)

    //we could use jackson if we got a JSON
    val objData = mapperAll.readTree(responseBody)

    println("My name is " + objData.get("name").textValue() + ", and I'm a " + objData.get("job").textValue() + ".")
}

Answer 3

Have a look at Fuel library, a sample GET request

"https://httpbin.org/get"
  .httpGet()
  .responseString { request, response, result ->
    when (result) {
      is Result.Failure -> {
        val ex = result.getException()
      }
      is Result.Success -> {
        val data = result.get()
      }
    }
  }

// You can also use Fuel.get("https://httpbin.org/get").responseString { ... }
// You can also use FuelManager.instance.get("...").responseString { ... }

A sample POST request

Fuel.post("https://httpbin.org/post")
    .jsonBody("{ \"foo\" : \"bar\" }")
    .also { println(it) }
    .response { result -> }

Their documentation can be found here ​

Answer 4

Without adding additional dependencies, this works. You don't need Volley for this. This works using the current version of Kotlin as of Dec 2018: Kotlin 1.3.10

If using Android Studio, you'll need to add this declaration in your AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

You should manually declare imports here. The auto-import tool caused me many conflicts.:

import android.os.AsyncTask
import java.io.BufferedReader
import java.io.InputStreamReader
import java.io.OutputStream
import java.io.OutputStreamWriter
import java.net.URL
import java.net.URLEncoder
import javax.net.ssl.HttpsURLConnection

You can't perform network requests on a background thread. You must subclass AsyncTask.

To call the method:

NetworkTask().execute(requestURL, queryString)

Declaration:

private class NetworkTask : AsyncTask<String, Int, Long>() {
    override fun doInBackground(vararg parts: String): Long? {
        val requestURL = parts.first()
        val queryString = parts.last()

        // Set up request
        val connection: HttpsURLConnection = URL(requestURL).openConnection() as HttpsURLConnection
        // Default is GET so you must override this for post
        connection.requestMethod = "POST"
        // To send a post body, output must be true
        connection.doOutput = true
        // Create the stream
        val outputStream: OutputStream = connection.outputStream
        // Create a writer container to pass the output over the stream
        val outputWriter = OutputStreamWriter(outputStream)
        // Add the string to the writer container
        outputWriter.write(queryString)
        // Send the data
        outputWriter.flush()

        // Create an input stream to read the response
        val inputStream = BufferedReader(InputStreamReader(connection.inputStream)).use {
            // Container for input stream data
            val response = StringBuffer()
            var inputLine = it.readLine()
            // Add each line to the response container
            while (inputLine != null) {
                response.append(inputLine)
                inputLine = it.readLine()
            }
            it.close()
            // TODO: Add main thread callback to parse response
            println(">>>> Response: $response")
        }
        connection.disconnect()

        return 0
    }

    protected fun onProgressUpdate(vararg progress: Int) {
    }

    override fun onPostExecute(result: Long?) {
    }
}