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 alread

Answer 1

If you are using Kotlin, you might as well keep your code as succinct as possible. The run method turns the receiver into this and returns the value of the block. this as HttpURLConnection creates a smart cast. bufferedReader().readText() avoids a bunch of boilerplate code.

return URL(url).run {
        openConnection().run {
            this as HttpURLConnection
            inputStream.bufferedReader().readText()
        }
}

You can also wrap this into an extension function.

fun URL.getText(): String {
    return openConnection().run {
                this as HttpURLConnection
                inputStream.bufferedReader().readText()
            }
}

And call it like this

return URL(url).getText()

Finally, if you are super lazy, you can extend the String class instead.

fun String.getUrlText(): String {
    return URL(this).run {
            openConnection().run {
                this as HttpURLConnection
                inputStream.bufferedReader().readText()
            }
    }
}

And call it like this

return "http://somewhere.com".getUrlText()

Answer 2

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 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

Send HTTP POST/GET request with parameters using HttpURLConnection :

POST with Parameters:

fun sendPostRequest(userName:String, password:String) {

    var reqParam = URLEncoder.encode("username", "UTF-8") + "=" + URLEncoder.encode(userName, "UTF-8")
    reqParam += "&" + URLEncoder.encode("password", "UTF-8") + "=" + URLEncoder.encode(password, "UTF-8")
    val mURL = URL("<Your API Link>")

    with(mURL.openConnection() as HttpURLConnection) {
        // optional default is GET
        requestMethod = "POST"

        val wr = OutputStreamWriter(getOutputStream());
        wr.write(reqParam);
        wr.flush();

        println("URL : $url")
        println("Response Code : $responseCode")

        BufferedReader(InputStreamReader(inputStream)).use {
            val response = StringBuffer()

            var inputLine = it.readLine()
            while (inputLine != null) {
                response.append(inputLine)
                inputLine = it.readLine()
            }
            println("Response : $response")
        }
    }
}

GET with Parameters:

fun sendGetRequest(userName:String, password:String) {

        var reqParam = URLEncoder.encode("username", "UTF-8") + "=" + URLEncoder.encode(userName, "UTF-8")
        reqParam += "&" + URLEncoder.encode("password", "UTF-8") + "=" + URLEncoder.encode(password, "UTF-8")

        val mURL = URL("<Yout API Link>?"+reqParam)

        with(mURL.openConnection() as HttpURLConnection) {
            // optional default is GET
            requestMethod = "GET"

            println("URL : $url")
            println("Response Code : $responseCode")

            BufferedReader(InputStreamReader(inputStream)).use {
                val response = StringBuffer()

                var inputLine = it.readLine()
                while (inputLine != null) {
                    response.append(inputLine)
                    inputLine = it.readLine()
                }
                it.close()
                println("Response : $response")
            }
        }
    }

Answer 5

You can use kohttp library. It is a Kotlin DSL HTTP client. It supports the features of square.okhttp and provides a clear DSL for them. KoHttp async calls are powered by coroutines.

httpGet extension function

val response: Response = "https://google.com/search?q=iphone".httpGet()

you can also use async call with coroutines

val response: Deferred<Response> = "https://google.com/search?q=iphone".asyncHttpGet()

or DSL function for more complex requests

val response: Response = httpGet {
    host = "google.com"
    path = "/search"
    param {
       "q" to "iphone"
       "safe" to "off"
   }
}

You can find more details in docs

To get it with gradle use

implementation 'io.github.rybalkinsd:kohttp:0.12.0'