Introduction
Client Server communication is an important aspect in android programming. Ideally we retrieve data from server to display it on android screen (web based android application). This tutorial describes how to implement client server communication step by step.
How to retrieve Data from Server?
Grand Permission to Access Network
Grant internet access in AndroidManifest.xml file with the following content
<uses-permission android:name="android.permission.INTERNET"></uses-permission>
On button click URL will get hit
button.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// Create Object and call AsyncTask execute Method
new WebServiceCall().execute();
}
});
Check if network is connected
Code to check if network is connected. Call the below method before calling the actual URL
private boolean isNetworkConnected() {
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo ni = cm.getActiveNetworkInfo();
if (ni == null) {
// There are no active networks.
return false;
} else {
return true;
}
}
Retrieve Data fro Server
Below code will retrieve data from the server. Follow inline comments to understand the code
public class WebServiceCall extends AsyncTask<Void, Void, String> {
@Override
protected void onPreExecute() { // At first This method will get called. Check the network connection here
super.onPreExecute();
if(!isNetworkConnected()) { // Check internet connectivity before hitting the actual URL
Toast.makeText(getApplicationContext(),"NO INTERNET CONNECTION",Toast.LENGTH_LONG).show();
}
}
@Override
//Once the network is connected, this method will hit the URL to fetch data from server. This will be done at the background
protected String doInBackground(Void... params) {
HttpClient httpClient = new DefaultHttpClient();
HttpContext localContext = new BasicHttpContext();
String url = "www.google.com"; // This URL will be hit from android client
HttpGet httpGet = new HttpGet(url);
String text = null;
try {
HttpResponse response = httpClient.execute(httpGet, localContext);
HttpEntity entity = response.getEntity();
text = getASCIIContentFromEntity(entity);
} catch (Exception e) {
return e.getLocalizedMessage();
}
return text;
}
@Override
// This method will get called once doInBackground() method is completed. Here we can update the UI elements.
protected void onPostExecute(String results) {
if(results == null || results.length() < 100) {
// Write your logic to process data
}
}
// This method converts HttpEntity into ASCII content
protected String getASCIIContentFromEntity(HttpEntity entity) throws IllegalStateException, IOException {
InputStream in = entity.getContent();
StringBuffer out = new StringBuffer();
int n = 1;
while (n>0) {
byte[] b = new byte[4096];
n = in.read(b);
if (n>0) out.append(new String(b, 0, n));
}
return out.toString();
}
}
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