Android | Connecting to the Network Using HttpUrlConnection

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android-recyclerview-listadapter_files.png

One common task for most Android apps is connecting to the Internet. Most network-connected Android apps use HTTP to send and receive data. This article shows you how to write a simple application that connects to the Internet, send HTTP GET request & display the response.

Objectives

  • How to send HTTP GET request to a web server and display the response?
  • How to check network connection?
  • How to use AsyncTask to perform network operations on a separate thread?

Environment & Tools

Tools used in this post

About this Sample App

We will build an app that send HTTP GET request and display the response.

( 1 ) Create new Android Project

  • Project Name: android-http
  • Package Name: com.hmkcode.http
  • Minimum SDK: API 19: Android 4.4 (KitKat)

( 2 ) Add Permissions

  • Add the following two lines to the AndroidMainifest.xml file
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Starting with Android 9 (API level 28), cleartext support is disabled by default.

cleartext traffic

<application
        ...
        android:usesCleartextTraffic="true"
        ...
</application>

( 2 ) Design App Layout

  • Add two TextView to activity_main.xml .
  • First TextView for displaying network connection info.
  • Second TextView to display message from server.

android-recyclerview-listadapter_files.png

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout ...>

    <TextView
        android:id="@+id/tvIsConnected"
        .../>

    <TextView
        android:id="@+id/tvResult"
        .../>
</LinearLayout>

( 3 ) Check the Network Connection

  • Before making any network operation you need to check if you are connected or not.
  • To check whether a network connection is available use getActiveNetworkInfo() and isConnected().
private fun checkNetworkConnection(): Boolean {
    val cm:ConnectivityManager =
        getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager

    val networkInfo:NetworkInfo? = cm.activeNetworkInfo
    val isConnected: Boolean = if(networkInfo != null) networkInfo.isConnected() else false

    if(isConnected){
        tvIsConnected.setText("Connected "+networkInfo?.typeName)
        tvIsConnected.setBackgroundColor(0xFF7CCC26.toInt())

    }else{
        tvIsConnected.setText("Not Connected!")
        tvIsConnected.setBackgroundColor(0xFFFF0000.toInt())
    }
    return isConnected;
}

( 4 ) Perform HTTP GET Request

  • The simplest example for network operation is HTTP GET request.
  • We create a new URL object by passing url string to the constructor.
  • The URL object is used to establish an HttpURLConnection.
  • Then, we execute the operation and receive the response as InputStream.
  • Finally, we use helper method to convert InputStream to string.
private fun HttpGet(myURL: String?): String {

    val inputStream:InputStream
    val result:String

    // create URL
    val url:URL = URL(myURL)

    // create HttpURLConnection
    val conn:HttpURLConnection = url.openConnection() as HttpURLConnection

    // make GET request to the given URL
    conn.connect()

    // receive response as inputStream
    inputStream = conn.inputStream

    // convert inputstream to string
    if(inputStream != null)
        result = convertInputStreamToString(inputStream)
    else
        result = "Did not work!"
    
    return result
}

( 5 ) Perform Network Operations on a Separate Thread

  • Network operation should always run on a seperate thread to avoid UI freeze.
  • The AsyncTask class provides one of the simplest ways to create separate thread from the UI thread.
  • Create an inner class extending AsyncTask.
  • Override doInBackground() & onPostExecute.
inner class HTTPAsyncTask : AsyncTask<String, Void, String>() {
    override fun doInBackground(vararg urls: String?): String {
        return HttpGet(urls[0])
    }
    override fun onPostExecute(result: String?) {
        tvResult.setText(result)
    }
}

( 6 ) Convert the InputStream to a String

  • We will use a helper method to convert InputStream byte into String
private fun convertInputStreamToString(inputStream: InputStream): String {
    val bufferedReader:BufferedReader? = BufferedReader(InputStreamReader(inputStream))
    var line:String? = bufferedReader?.readLine()
    var result:String = ""

    while (line != null) {
        result += line
        line = bufferedReader?.readLine()
    }

    inputStream.close()
    return result
}

Source Code @ GitHub

Exploring Kotlin

Less than 100 pages covering Kotlin syntax and features in straight and to the point explanation.