Android with Kotlin - How to use HttpUrlConnection

Android with Kotlin - How to use HttpUrlConnection - android

I´m trying to get data from a url inside an AsyncTask but I get an error when creating a new instance of HttpUrlConnection.
Something like this on Java
URL url = new URL("http://www.android.com/");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
try {
InputStream in = new BufferedInputStream(urlConnection.getInputStream());
readStream(in);
finally {
urlConnection.disconnect();
}
But I keep getting the error shown below.
class GetWeatherTask : AsyncTast<Void, Void, Void>() {
override fun doInBackground(vararg params: Void?): Void? {
val httpClient = HttpURLConnection();
return null
}
override fun onPreExecute() {
super.onPreExecute()
}
override fun onPostExecute(result: Void?) {
super.onPostExecute(result)
}
}
Cannot access '': it is 'protected/protected and package/' in 'HttpURLConnection' Cannot create an instance of an abstract class
Am I missing something? I tryied to create a class object extending HttpUrlConnection and try to implement the init method but I couldn't
Thanks in advance.

Here is a simplification of the question and answer.
Why does this fail?
val connection = HttpURLConnection()
val data = connection.inputStream.bufferedReader().readText()
// ... do something with "data"
with error:
Kotlin: Cannot access '': it is 'protected/protected and package/' in 'HttpURLConnection'
This fails because you are constructing a class that is not intended to directly be constructed. It is meant to be created by a factory, which is in the URL class openConnection() method. This is also not a direct port of the sample Java code in the original question.
The most idiomatic way in Kotlin to open this connection and read the contents as a string would be:
val connection = URL("http://www.android.com/").openConnection() as HttpURLConnection
val data = connection.inputStream.bufferedReader().readText()
This form will auto close everything when done reading the text or on an exception. If you want to do custom reading:
val connection = URL("http://www.android.com/").openConnection() as HttpURLConnection
connection.inputStream.bufferedReader().use { reader ->
// ... do something with the reader
}
NOTE: the use() extension function will open and close the reader and handle closing on errors automatically.
About the disconnect() method
The docs for disconnect say:
Each HttpURLConnection instance is used to make a single request
but the underlying network connection to the HTTP server may be
transparently shared by other instances. Calling the close() methods
on the InputStream or OutputStream of an HttpURLConnection
after a request may free network resources associated with this
instance but has no effect on any shared persistent connection.
Calling the disconnect() method may close the underlying socket
if a persistent connection is otherwise idle at that time.
So you decide if you want to call it or not. Here is a version of the code that calls disconnect:
val connection = URL("http://www.android.com/").openConnection() as HttpURLConnection
try {
val data = connection.inputStream.bufferedReader().use { it.readText() }
// ... do something with "data"
} finally {
connection.disconnect()
}

The simplest way to do a get post request using HTTPUrlConnection is to create a common helper class that can be called from anywhere in the app to call the GET and POST request methods, without writing the same code again and again.
Below is the helper object (Singleton) class that you can use for the network call for GET and POST requests.
package com.dewari.ajay.androidnetworkcommunication.network
import org.json.JSONObject
import java.io.BufferedReader
import java.io.BufferedWriter
import java.io.IOException
import java.io.InputStreamReader
import java.io.OutputStream
import java.io.OutputStreamWriter
import java.net.HttpURLConnection
import java.net.URL
import java.net.URLEncoder
import javax.net.ssl.HttpsURLConnection
object RequestHandler {
const val GET : String = "GET"
const val POST : String = "POST"
#Throws(IOException::class)
fun requestPOST(r_url: String?, postDataParams: JSONObject): String? {
val url = URL(r_url)
val conn: HttpURLConnection = url.openConnection() as HttpURLConnection
conn.readTimeout = 3000
conn.connectTimeout = 3000
conn.requestMethod = POST
conn.doInput = true
conn.doOutput = true
val os: OutputStream = conn.outputStream
val writer = BufferedWriter(OutputStreamWriter(os, "UTF-8"))
writer.write(encodeParams(postDataParams))
writer.flush()
writer.close()
os.close()
val responseCode: Int = conn.responseCode // To Check for 200
if (responseCode == HttpsURLConnection.HTTP_OK) {
val `in` = BufferedReader(InputStreamReader(conn.inputStream))
val sb = StringBuffer("")
var line: String? = ""
while (`in`.readLine().also { line = it } != null) {
sb.append(line)
break
}
`in`.close()
return sb.toString()
}
return null
}
#Throws(IOException::class)
fun requestGET(url: String?): String? {
val obj = URL(url)
val con = obj.openConnection() as HttpURLConnection
con.requestMethod = GET
val responseCode = con.responseCode
println("Response Code :: $responseCode")
return if (responseCode == HttpURLConnection.HTTP_OK) { // connection ok
val `in` =
BufferedReader(InputStreamReader(con.inputStream))
var inputLine: String?
val response = StringBuffer()
while (`in`.readLine().also { inputLine = it } != null) {
response.append(inputLine)
}
`in`.close()
response.toString()
} else {
""
}
}
#Throws(IOException::class)
private fun encodeParams(params: JSONObject): String? {
val result = StringBuilder()
var first = true
val itr = params.keys()
while (itr.hasNext()) {
val key = itr.next()
val value = params[key]
if (first) first = false else result.append("&")
result.append(URLEncoder.encode(key, "UTF-8"))
result.append("=")
result.append(URLEncoder.encode(value.toString(), "UTF-8"))
}
return result.toString()
}
}
Using the above object class you can do your GET and POST requests as shown below:
//As this is network call it should be done in a separate thread
Thread(Runnable {
RequestHandler.requestGET(url)
RequestHandler.requestPOST(url, postJSONObject)
}).start()
Instead of using thread you can also use AsyncTask as followed:
class NetworkAsyncCall(private val context: Context, private val url: String, private val requestType:
String, private val postJSONObject: JSONObject = JSONObject()
) : AsyncTask<String?, String?, String?>() {
override fun doInBackground(vararg p0: String?): String? {
return when (requestType) {
RequestHandler.GET -> RequestHandler.requestGET(url)
RequestHandler.GET -> RequestHandler.requestPOST(url, postJSONObject)
else -> ""
}
}
override fun onPostExecute(s: String?) {
if (s != null) {
Toast.makeText(context, s, Toast.LENGTH_LONG).show()
}
}
}
You can create the asyncTask as a inner class of Activity or a seperate indipendent class.
Now to call the newtwork call via the AsyncTask NetworkAsyncCall in your onCreate() or any function from which you want call the api you can write:
NOTE: The mentioned url will not work so, you have to replace it with your own.
override fun onCreate(savedInstanceState: Bundle?) {
setContentView(R.layout.activity_main)
// Change the url with your own GET URL request
val urlGET = "http://my-json-feed"
//GET Request
NetworkAsyncCall(this#MainActivity, urlGET, RequestHandler.GET).execute();
// POST Request
// doPost()
}
For POST request you can call:
private fun doPost() {
// Change the url with your own POST URL request
val urlPOST = "http://my-json-feed"
val postDataParams = JSONObject()
postDataParams.put("name", "Ajay")
postDataParams.put("email", "aj****ri#gmail.com")
postDataParams.put("phone", "+91 78******25")
NetworkAsyncCall(this#MainActivity, urlPOST, RequestHandler.POST, postDataParams).execute()
}
you can check the complete code in github here.
For a good explanation you can check this link.
the advantage of using the NetworkAsyncCall as seperate indipendent class is you don't have to write the AsyncTask code again, just call the same AsyncTask NetworkAsyncCall with a new object from different activitys/functions, however with this you have to implement a listener interface that you will require for the callback on onPostExecute() after getting the response from the api and to return back the response to the activity you have to perform the callback using that interface.

You can adaptaion your code; Don't forget user Runnable thread.
Thread(Runnable {
try {
val url = URL("www.android.com")
val con = url.openConnection() as HttpURLConnection
val datas = con.inputStream.bufferedReader().readText()
val json = JSONObject(datas)
val blockList = json.getJSONObject("blockList")
val warning = json.get("warnMessage").toString()
val keys = blockList.keys()
var permission = HashMap<String, Array<String?>>()
while (keys.hasNext()) {
val key = keys.next()
val kods = blockList.getJSONArray(key)
val permissonArray = arrayOfNulls<String>(kods.length())
for (i in permissonArray.indices) {
permissonArray[i] = kods.getString(i)
}
permission[key] = permissonArray;
}
} catch (ex: Exception) {
Log.d("Exception", ex.toString())
}
}).start()

Related

Android generic Gson.fromJson() conversion with coroutine and flow

I am making generic classes for hitting otp api.anybody can use otp section just have to pass request ,Response class and url and all will be done by this otp section.
Please note : this response class can be of different type (for eg: MobileOtpResponse,EmailOtpResponse)
below is the generic OtpClient which takes any request type and returns particular passed ResponseType (for example : Request class passed is OtpRequest ,ResponseType class passed is OtpResponse)
interface OtpClient {
#POST
suspend fun <Request : Any, ResponseType> sendOtp(#Url url: String,
#Body request:#JvmSuppressWildcards Any): #JvmSuppressWildcards ResponseType
}
OtpRequest
data class OtpRequest(#SerializedName("mobile_number") val mobileNumber: String,#SerializedName("app_version") val appVersion: String)
OtpResponse
data class OtpResponse(#SerializedName("status") val status: String = "",
#SerializedName("response") val response: OtpData? = null)
data class OtpData(
#SerializedName("otp_status") val otpStatus: Boolean = false,
#SerializedName("message") val message: String = "",
#SerializedName("error") val error: Int? = null,
#SerializedName("otp_length") val otpLength: Int? = null,
#SerializedName("retry_left") val retryLeft: Int? = null,)
Now i create Repo to call this api this simply use flow and when the data fetch it emits the data
class OtpRepoImpl<out Client : OtpClient>(val client: Client) :OtpRepo {
override fun <Request:Any, ResponseType> sentOtpApi(url: String, request: Request): Flow<ResponseType> {
return flow<ResponseType> {
// exectute API call and map to UI object
val otpResponse = client.sendOtp<Request, ResponseType>(url,request)
emit(otpResponse)
}.flowOn(Dispatchers.IO) // Use the IO thread for this Flow
}
}
this repo is used in viewmodel class
#ExperimentalCoroutinesApi
fun <A : Class<ResponseType>, Request : Any, ResponseType : Any> sendOtp(a: Class<ResponseType>, request: Request, response: ResponseType, url: String) {
viewModelScope.launch {
repo.sentOtpApi<Request, ResponseType>(url, request = request)
.onStart { _uiState.value = OtpState.Loading(true) }
.catch { cause ->
_uiState.value = OtpState.Loading(false)
getResponseFromError<Class<ResponseType>,ResponseType>(cause, response) {
// emit(it)
}
}
.collect {
_uiState.value = OtpState.Loading(false)
_uiState.value = OtpState.Success(it)
}
}
}
as you can see above this sendOtp method is called from the view class and inside this method we use repo.sentOtpApi and pass generic request response type.I get data in catch block coz api is send error otp data in 400 HttpException so i created another method getResponseFromError to get error response it should parse the errorBody response and call this lambda block.
private suspend fun <A : Class<*>, ResponseType : Any> getResponseFromError( cause: Throwable, rp: ResponseType, block: suspend (ResponseType) -> Unit) {
if (cause is HttpException) {
val response = cause.response()
if (response?.code() == 400) {
println("fetching error Response")
val errorResponse = response.errorBody()?.charStream()
val turnsType = object : TypeToken<ResponseType>() {}.type
val finalErrorResponse = Gson().fromJson<ResponseType>(errorResponse, turnsType)
block(finalErrorResponse)
} else {
println("someOther exception")
}
} else
_uiState.value = OtpState.Error(cause)
}
so here i am facing the problem inside above method
val turnsType = object : TypeToken<ResponseType>() {}.type
val finalErrorResponse = Gson().fromJson<ResponseType>(errorResponse, turnsType)
block(finalErrorResponse)
This finalErrorResponse is returning LinkedTreeMap instead of ResponseType (in this case its OtpResponse)
i have also tried using Class<*> type like this
val turnsType = object : TypeToken<A>() {}.type
val finalErrorResponse = Gson().fromJson<A>(errorResponse, turnsType)
but its not working.
calling of this sentOtp viewmodel func is like
var classType = OtpResponse::class.java
otpViewModel.sendOtp(a = classType, request = otpRequest, response = OtpResponse() , url =
"http://preprod-api.nykaa.com/user/otp/v2/send-wallet-otp")
[![value in finalErroResponse][1]][1]
[1]: https://i.stack.imgur.com/Holui.png
required: finalErroResponse should be of OtpResponse type because that was passed in sentOtp func
Please help :)

Change DNS on all requests

I need to change DNS on all Android requests. How to get it done?
I found this:
class HTTPDNSInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
val originRequest = chain.request()
val httpUrl = originRequest.url()
val url = httpUrl.toString()
val host = httpUrl.host()
val hostIP = HttpDNS.getIpByHost(host)
val builder = originRequest.newBuilder()
if (hostIP != null) {
builder.url(HttpDNS.getIpUrl(url, host, hostIP))
builder.header("host", hostIP)
}
val newRequest = builder.build()
val newResponse = chain.proceed(newRequest)
return newResponse
}
}
But, I don't have all the helper classes and I have not found any library where I can explicitly set certain DNS. Even if there is a way to dynamically check valid DNS and setting any working, would be great too.

Android: HTTP request with Volley fails to call with parameters

I deployed a NLP model as an API with Flask. Now I want to call the API from my simple Android app to process some text and to return a prediction, however when the Android App performs the HTTP request using Volley it does not add the parameters in the URL for some reason. Here is the code:
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// button
val showButton = findViewById<Button>(R.id.showInput)
// text
val editText = findViewById<EditText>(R.id.editText)
// Setting On Click Listener
showButton.setOnClickListener {
// user input
val text = editText.text
// Instantiate the RequestQueue.
val queue = Volley.newRequestQueue(this)
val url = "http://192.168.100.12:5000/"
// Request a string response from the provided URL.
val request = object : StringRequest(Request.Method.POST,
url,
Response.Listener {
response ->
editText.setText(response.toString())
},
Response.ErrorListener { error ->
Log.i("error ", error.toString())
editText.setText("Volley error: $it ")
}) {
override fun getBodyContentType(): String {
return "application/json"
}
#Throws(AuthFailureError::class)
override fun getBody(): ByteArray {
val params = HashMap<String,String>()
params.put("text", text.toString())
return params.toString().toByteArray()
}
}
// Add the request to the RequestQueue.
queue.add(request)
// Showing the response
Toast.makeText(this, text, Toast.LENGTH_SHORT).show()
}
}
}
In essence, I am expecting the URL to be "http://192.168.100.12:5000/?text=<insert_text_here>", but the actual URL that the app calls is just "http://192.168.100.12:5000" without the parameters.
I know this because my Flask app returns this error:
AttributeError: 'NoneType' object has no attribute 'lower'
The error response code is 500.
I tested the Flask API with both the browser and Postman and it is working fine, but just in case I will leave the code here:
from flask import Flask,render_template,url_for,request,jsonify
from sklearn.externals import joblib
import traceback
app = Flask(__name__)
#app.route("/",methods=['GET','POST'])
def predict():
try:
tweet = request.args.get('text')
model = open('model.pkl','rb')
model = joblib.load(model)
prediction = model.predict([tweet])
if prediction == [0]:
return 'This tweet does not violate our Community Guidelines'
else:
return 'This tweet violates out Community Guidelines for hate speech'
except:
return traceback.format_exc()
if __name__ == '__main__':
app.run(host = '192.168.100.12',debug=True)
So far I also have tried the code from this post as well as using the GET method with getParams() function instead of getBody() as shown below, but none of them worked.
#Throws(AuthFailureError::class)
override fun getParams(): Map<String, String>? {
val params: HashMap<String, String> = HashMap()
params["text"] = text.toString()
return params
}
Can you please help me solve this issue? I would be very grateful.

Ping website URL before loading it in WebView in Android Kotlin

Before loading a website in WebView, I want to check the URL and make sure that it loads. If it does, show the WebView; if not, show another View with a message.
The idea is to check if the website can be loaded and depending on the response show either the "Website cannot be loaded" screen or show the WebView with URL loaded.
I have already checked if the connection is available, so no need to worry about that.
Need to support API 25+.

My solution below is trying to do two things:
Using AsyncTask "ping" a website and then
By passing context from MainActivity, call a function to show WebView (using WeakReference here to achieve that)
class MainActivity : AppCompatActivity() {
private var websiteURL = "https://www.google.com"
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// ...
webView.webViewClient = WebViewClient()
}
// I called this function after checking that there is Internet connection
private fun connectionResponseFunction(): String {
return if (isConnected) {
// *** is connected
// pass in "this" context from MainActivity
val downloadData = CheckLink(this)
downloadData.execute(websiteURL)
} else {
// *** not connected
}
}
private fun showWebView() {
webView.loadUrl(websiteURL)
}
companion object {
class CheckLink internal constructor(context: MainActivity) : AsyncTask<String, Void, String>() {
// Needed if you want to use webView or anything else from MainActivity
private val activityReference: WeakReference<MainActivity> = WeakReference(context)
override fun onPostExecute(result: String?) {
super.onPostExecute(result)
val activity = activityReference.get()
if (activity == null || activity.isFinishing) return
if (result == "success") {
// URL loaded, show webView
activity.showWebView()
} else {
// URL didn't load
}
}
override fun doInBackground(vararg url: String?): String {
val linkLoaded = loadLink(url[0])
if (!linkLoaded) {
return "failure"
}
return "success"
}
private fun loadLink(urlPath: String?): Boolean {
try {
val url = URL(urlPath)
val connection: HttpURLConnection = url.openConnection() as HttpURLConnection
connection.setRequestProperty("Connection", "close")
connection.connectTimeout = 3000
connection.connect()
val response = connection.responseCode
// 200 for success
return if (response == 200) {
true
} else {
false
}
} catch (e: Exception) {
// Handle exceptions
when (e) {
is MalformedURLException -> "loadLink: Invalid URL ${e.message}"
is IOException -> "loadLink: IO Exception reading data: ${e.message}"
is SecurityException -> { e.printStackTrace()
"loadLink: Security Exception. Needs permission? ${e.message}"
}
else -> "Unknown error: ${e.message}"
}
}
return false // Error
}
}
}
}
I'm quite new to Android and Kotlin, so I'm open to any suggestions to make it better.
I could not find any recent code that works for API 25+.

Another (shorter) alternative to AsyncTask would it be using Thread:
Thread {
val result = isHostAvailable(BuildConfig.BASE_URL)
runOnUiThread {
if (result) {
// do something ...
}
else showToast("no connection to server")
}
}.start()
and
fun isHostAvailable(urlPath: String): Boolean {
try {
val url = URL(urlPath)
val connection: HttpURLConnection = url.openConnection() as HttpURLConnection
connection.setRequestProperty("Connection", "close")
connection.connectTimeout = 3000
connection.connect()
return when (connection.responseCode) {
200, 403 -> true
else -> false
}
} catch (e: Exception) {
when (e) {
is MalformedURLException -> "loadLink: Invalid URL ${e.message}"
is IOException -> "loadLink: IO Exception reading data: ${e.message}"
is SecurityException -> {
e.printStackTrace()
"loadLink: Security Exception. Needs permission? ${e.message}"
}
else -> "Unknown error: ${e.message}"
}
}
return false
}

Looks like ping doesn't work on emulators (How to Ping External IP from Java Android)...instead, try this on a real device, it'll work:
val process = Runtime.getRuntime().exec("/system/bin/ping -c 1 $SERVIDOR")
val pingResult = process .waitFor()
return pingResult == 0
By the way, the answer given by #quietbits is pretty obsolete...AsyncTask class was the way to go like 5 years ago...Since Android Studio supports kotlin, you should use coroutines!! the code line difference is huge...check this code labs for more info (https://codelabs.developers.google.com/codelabs/kotlin-coroutines/#0)

HTTP Request in Android with 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.

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("http://www.google.com/")
with(url.openConnection() as HttpURLConnection) {
requestMethod = "GET" // optional default is GET
println("\nSent 'GET' request to URL : $url; Response Code : $responseCode")
inputStream.bufferedReader().use {
it.lines().forEach { line ->
println(line)
}
}
}
}
Or simpler:
URL("https://google.com").readText()

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")
}
}
}

Using only the standard library with minimal code!
thread {
val json = try {
URL(url).readText()
} catch (e: Exception) {
return#thread
}
runOnUiThread { displayOrWhatever(json) }
}
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 "glues" 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.

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

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 $token")
.url(url)
.post(body)
.build()
val response = client . newCall (request).execute()
println(response.request())
println(response.body()!!.string())
Remember to add this dependency to your project https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp
UPDATE: July 7th, 2019
I'm gonna give two examples using latest Kotlin (1.3.41), OkHttp (4.0.0) and Jackson (2.9.9).
UPDATE: January 25th, 2021
Everything is okay with the most updated versions.
<!-- https://mvnrepository.com/artifact/com.fasterxml.jackson.module/jackson-module-kotlin -->
<dependency>
<groupId>com.fasterxml.jackson.module</groupId>
<artifactId>jackson-module-kotlin</artifactId>
<version>2.12.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp -->
<dependency>
<groupId>com.squareup.okhttp3</groupId>
<artifactId>okhttp</artifactId>
<version>4.9.0</version>
</dependency>
Get Method
fun get() {
val client = OkHttpClient()
val url = URL("https://reqres.in/api/users?page=2")
val request = Request.Builder()
.url(url)
.get()
.build()
val response = client.newCall(request).execute()
val responseBody = response.body!!.string()
//Response
println("Response Body: " + responseBody)
//we could use jackson if we got a JSON
val mapperAll = ObjectMapper()
val objData = mapperAll.readTree(responseBody)
objData.get("data").forEachIndexed { index, jsonNode ->
println("$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() + ".")
}

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"
...

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()

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'

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?) {
}
}

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<MyObject>(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'

You can use this library Fuel Library as well, which makes it further easier.
val map = mutableMapOf<String, String>()
map.put("id","629eeb9da9d8f50016e1af96")
val httpAsync = url
.httpPost()
.jsonBody(
Gson().toJson(map) // for json string
)
.responseString { request, response, result -> //do something with the response }

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.

Android with Kotlin - How to use HttpUrlConnection - android

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