Introduction to Android Networking, Client Server

Android lets your application connect to the internet or any other local network and allows you to perform network operations.

A device can have various types of network connections. This chapter focuses on using either a Wi-Fi or a mobile network connection.

Checking Network Connection

Before you perform any network operations, you must first check that are you connected to that network or internet e.t.c. For this android provides ConnectivityManager class. You need to instantiate an object of this class by calling getSystemService() method. Its syntax is given below −

ConnectivityManager check = (ConnectivityManager) 
this.context.getSystemService(Context.CONNECTIVITY_SERVICE);  

Once you instantiate the object of ConnectivityManager class, you can use getAllNetworkInfo method to get the information of all the networks. This method returns an array of NetworkInfo. So you have to receive it like this.

NetworkInfo[] info = check.getAllNetworkInfo();

The last thing you need to do is to check Connected State of the network. Its syntax is given below −

for (int i = 0; i<info.length; i++){
   if (info[i].getState() == NetworkInfo.State.CONNECTED){
      Toast.makeText(context, "Internet is connected
      Toast.LENGTH_SHORT).show();
   }
}

Apart from this connected states, there are other states a network can achieve. They are listed below −

Sr.No	State
1	Connecting
2	Disconnected
3	Disconnecting
4	Suspended
5	Unknown

Performing Network Operations

After checking that you are connected to the internet, you can perform any network operation. Here we are fetching the html of a website from a url.

Android provides HttpURLConnection and URL class to handle these operations. You need to instantiate an object of URL class by providing the link of website. Its syntax is as follows −

String link = "http://www.google.com";
URL url = new URL(link);   

After that you need to call openConnection method of url class and receive it in a HttpURLConnection object. After that you need to call the connect method of HttpURLConnection class.

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.connect();      

And the last thing you need to do is to fetch the HTML from the website. For this you will use InputStream and BufferedReader class. Its syntax is given below −

InputStream is = conn.getInputStream();
BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
String webPage = "",data="";

while ((data = reader.readLine()) != null){
   webPage += data + "\n";
}

Apart from this connect method, there are other methods available in HttpURLConnection class. They are listed below −

Sr.No	Method & description
1	disconnect() This method releases this connection so that its resources may be either reused or closed
2	getRequestMethod() This method returns the request method which will be used to make the request to the remote HTTP server
3	getResponseCode() This method returns response code returned by the remote HTTP server
4	setRequestMethod(String method) This method Sets the request command which will be sent to the remote HTTP server
5	usingProxy() This method returns whether this connection uses a proxy server or not

Example

The below example demonstrates the use of HttpURLConnection class. It creates a basic application that allows you to download HTML from a given web page.

To experiment with this example, you need to run this on an actual device on which wifi internet is connected .

Steps	Description
1	You will use Android studio IDE to create an Android application under a package com.tutorialspoint.myapplication.
2	Modify src/MainActivity.java file to add Activity code.
4	Modify layout XML file res/layout/activity_main.xml add any GUI component if required.
6	Modify AndroidManifest.xml to add necessary permissions.
7	Run the application and choose a running android device and install the application on it and verify the results.