Kotlin: HTTP GET/POST sample code

Unfortunate, Coroutines are still experimental on the Kotlin 1.2. This code is a simple HTTP GET/POST with JSON by using the AsyncTask. Hope this will help you.

All source code is on GitHub.

package co.ubunifu.kotlinhttpsample

import android.os.AsyncTask
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.ProgressBar
import org.json.JSONArray
import org.json.JSONObject
import java.io.*
import java.net.HttpURLConnection
import java.net.URL

operator fun JSONArray.iterator(): Iterator<JSONObject> =
        (0 until length()).asSequence().map { get(it) as JSONObject }.iterator()

val TIMEOUT = 10*1000

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val progressBar = findViewById<ProgressBar>(R.id.progressBar)
        progressBar.visibility = View.INVISIBLE

        val button = findViewById<Button>(R.id.buttonGet)
        button.setOnClickListener() {
            progressBar.visibility = View.VISIBLE
            HttpTask( {
                progressBar.visibility = View.INVISIBLE
                if (it == null) {
                    println("connection error")
                    return@HttpTask
                }
                for (json in JSONArray(it)) {
                    println(json)
                }
            } ).execute("GET", "http://192.168.33.10/api/articles")
        }

        val buttonPost = findViewById<Button>(R.id.buttonPost)
        buttonPost.setOnClickListener() {

            val json = JSONObject()
            json.put("title", "TITLE")
            json.put("content", "CONTENT")
            json.put("done", false)

            progressBar.visibility = View.VISIBLE
            HttpTask( {
                progressBar.visibility = View.INVISIBLE
                if (it == null) {
                    println("connection error")
                    return@HttpTask
                }
                println(it)
            } ).execute("POST", "http://192.168.33.10/api/article/1", json.toString())
        }

    }

    class HttpTask(callback: (String?) -> Unit) : AsyncTask<String, Unit, String>()  {

        var callback = callback

        override fun doInBackground(vararg params: String): String? {
            val url = URL(params[1])
            val httpClient = url.openConnection() as HttpURLConnection
            httpClient.setReadTimeout(TIMEOUT)
            httpClient.setConnectTimeout(TIMEOUT)
            httpClient.requestMethod = params[0]

            if (params[0] == "POST") {
                httpClient.instanceFollowRedirects = false
                httpClient.doOutput = true
                httpClient.doInput = true
                httpClient.useCaches = false
                httpClient.setRequestProperty("Content-Type", "application/json; charset=utf-8")
            }
            try {
                if (params[0] == "POST") {
                    httpClient.connect()
                    val os = httpClient.getOutputStream()
                    val writer = BufferedWriter(OutputStreamWriter(os, "UTF-8"))
                    writer.write(params[2])
                    writer.flush()
                    writer.close()
                    os.close()
                }
                if (httpClient.responseCode == HttpURLConnection.HTTP_OK) {
                    val stream = BufferedInputStream(httpClient.inputStream)
                    val data: String = readStream(inputStream = stream)
                    return data
                } else {
                    println("ERROR ${httpClient.responseCode}")
                }
            } catch (e: Exception) {
                e.printStackTrace()
            } finally {
                httpClient.disconnect()
            }

            return null
        }

        fun readStream(inputStream: BufferedInputStream): String {
            val bufferedReader = BufferedReader(InputStreamReader(inputStream))
            val stringBuilder = StringBuilder()
            bufferedReader.forEachLine { stringBuilder.append(it) }
            return stringBuilder.toString()
        }

        override fun onPostExecute(result: String?) {
            super.onPostExecute(result)
            callback(result)
        }
    }

    companion object {
        val TAG = "MainActivity"
    }
}

When Coroutines will be available. code might be more simple. 😗