Android | Connecting to the Network Using HttpUrlConnection

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

Android Studio 3.5
Google Pixel 3
Kotlin
http://hmkcode-api.appspot.com/rest/api/hello/[NAME] this URL will return simple string “Hello, [NAME]”

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.

<?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
}