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

User · Answer

Have a look at Fuel library  a sample GET request   https   httpbin org get     httpGet      responseString   request  response  result - gt      when  result          is Result Failure - gt            val ex   result getException                 is Result Success - gt            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 - gt      Their documentation can be found here

User · Answer

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

User · Answer

Using only the standard library with minimal code  thread       val jsonStr   try   URL url  readText     catch  ex  Exception    return thread       runOnUiThread   displayOrWhatever jsonStr       This starts a GET request on a new thread  leaving the UI thread to respond to user input  However  we can only modify UI elements from the main UI thread  so we actually need a runOnUiThread block to show the result to our user  This enqueues our display code to be run on the UI thread soon  The try catch is there so your app won t crash if you make a request with your phone s internet off  Add your own error handling  e g  showing a Toast  as you please   readText   is not part of the java net URL class but a Kotlin extension method  Kotlin  quot glues quot  this method onto URL  This is enough for plain GET requests  but for more control and POST requests you need something like the Fuel library

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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

User · Answer

GET and POST using OkHttp  private const val CONNECT TIMEOUT   15L private const val READ TIMEOUT   15L private const val WRITE TIMEOUT   15L  private fun performPostOperation urlString  String  jsonString  String  token  String   String        return try           val client   OkHttpClient Builder                connectTimeout CONNECT TIMEOUT  TimeUnit SECONDS               writeTimeout WRITE TIMEOUT  TimeUnit SECONDS               readTimeout READ TIMEOUT  TimeUnit SECONDS               build            val body   jsonString toRequestBody  application json  charset utf-8  toMediaTypeOrNull             val request   Request Builder                url URL urlString                header  Authorization   token               post body               build            val response   client newCall request  execute           response body  string             catch  e  IOException            e printStackTrace           null          private fun performGetOperation urlString  String  token  String   String        return try           val client   OkHttpClient Builder                connectTimeout CONNECT TIMEOUT  TimeUnit SECONDS               writeTimeout WRITE TIMEOUT  TimeUnit SECONDS               readTimeout READ TIMEOUT  TimeUnit SECONDS               build            val request   Request Builder                url URL urlString                header  Authorization   token               get                build            val response   client newCall request  execute           response body  string             catch  e  IOException            e printStackTrace           null           Object serialization and deserialization   Throws JsonProcessingException  class  fun objectToJson obj  Any   String       return ObjectMapper   writeValueAsString obj      Throws IOException  class  fun jsonToAgentObject json  String    MyObject        return if  json    null    null   else           ObjectMapper   readValue lt MyObject gt  json  MyObject  class java            Dependencies  Put the following lines in your gradle  app  file  Jackson is optional  You can use it for object serialization and deserialization   implementation  com squareup okhttp3 okhttp 4 3 1  implementation  com fasterxml jackson core jackson-core 2 9 8  implementation  com fasterxml jackson core jackson-annotations 2 9 8  implementation  com fasterxml jackson core jackson-databind 2 9 8

User · Answer

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 lt Response gt     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

User · Answer

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    quot https   example com endpoint quot   val client   OkHttpClient    val JSON   MediaType get  quot application json  charset utf-8 quot   val body   RequestBody create JSON   quot    quot data  quot    quot  data  quot   quot   val request   Request Builder            addHeader  quot Authorization quot    quot Bearer  token quot            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   UPDATE  January 25th  2021 Everything is okay with the most updated versions   lt  -- https   mvnrepository com artifact com fasterxml jackson module jackson-module-kotlin -- gt           lt dependency gt               lt groupId gt com fasterxml jackson module lt  groupId gt               lt artifactId gt jackson-module-kotlin lt  artifactId gt               lt version gt 2 12 1 lt  version gt           lt  dependency gt    lt  -- https   mvnrepository com artifact com squareup okhttp3 okhttp -- gt           lt dependency gt               lt groupId gt com squareup okhttp3 lt  groupId gt               lt artifactId gt okhttp lt  artifactId gt               lt version gt 4 9 0 lt  version gt           lt  dependency gt   Get Method fun get         val client   OkHttpClient       val url   URL  quot https   reqres in api users page 2 quot        val request   Request Builder                url url               get                build        val response   client newCall request  execute        val responseBody   response body   string          Response     println  quot Response Body   quot    responseBody         we could use jackson if we got a JSON     val mapperAll   ObjectMapper       val objData   mapperAll readTree responseBody       objData get  quot data quot   forEachIndexed   index  jsonNode - gt          println  quot  index  jsonNode quot            POST Method fun post         val client   OkHttpClient       val url   URL  quot https   reqres in api users quot          just a string     var jsonString    quot    quot name  quot     quot Rolando  quot     quot job  quot     quot Fakeador  quot   quot         or using jackson     val mapperAll   ObjectMapper       val jacksonObj   mapperAll createObjectNode       jacksonObj put  quot name quot    quot Rolando quot       jacksonObj put  quot job quot    quot Fakeador quot       val jacksonString   jacksonObj toString        val mediaType    quot application json  charset utf-8 quot  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  quot Response Body   quot    responseBody         we could use jackson if we got a JSON     val objData   mapperAll readTree responseBody       println  quot My name is  quot    objData get  quot name quot   textValue      quot   and I m a  quot    objData get  quot job quot   textValue      quot   quot

User · Answer

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      amp     URLEncoder encode  password    UTF-8           URLEncoder encode password   UTF-8       val mURL   URL   lt Your API Link gt         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      amp     URLEncoder encode  password    UTF-8           URLEncoder encode password   UTF-8            val mURL   URL   lt Yout API Link gt    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

User · Answer

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    lt uses-permission android name  android permission INTERNET    gt   lt uses-permission android name  android permission ACCESS NETWORK STATE    gt    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 lt String  Int  Long gt          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   gt  gt  gt  gt  Response   response                     connection disconnect            return 0            protected fun onProgressUpdate vararg progress  Int               override fun onPostExecute result  Long

User · Answer

Maybe the simplest GET  For everybody stuck with NetworkOnMainThreadException for the other solutions  use AsyncTask or  even shorter   yet still experimental  Coroutines   launch        val jsonStr   URL  url   readText          If you need to test with plain http don t forget to add to your manifest  android usesCleartextTraffic  true     For the experimental Coroutines you have to add to build gradle as of 10 10 2018   kotlin       experimental           coroutines  enable          dependencies       implementation  org jetbrains kotlinx kotlinx-coroutines-core 0 24 0      implementation  org jetbrains kotlinx kotlinx-coroutines-android 0 24 0

User · Answer

For Android  Volley is a good place to get started  For all platforms  you might also want to check out ktor client or http4k which are both good libraries  However  you can also use standard Java libraries like java net HttpURLConnection which is part of the Java SDK  fun sendGet         val url   URL  quot http   www google com  quot        with url openConnection   as HttpURLConnection            requestMethod    quot GET quot      optional default is GET          println  quot  nSent  GET  request to URL    url  Response Code    responseCode quot            inputStream bufferedReader   use               it lines   forEach   line - gt                  println line                                   Or simpler  URL  quot https   google com quot   readText

[android] HTTP Request in Kotlin

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