"sending post data in android" Code Answer

Note (Oct 2020): AsyncTask used in the following answer has been deprecated in Android API level 30. Please refer to Official documentation or this blog post for a more updated example

Updated (June 2017) Answer which works on Android 6.0+. Thanks to @Rohit Suthar, @Tamis Bolvari and @sudhiskr for the comments.

    public class CallAPI extends AsyncTask<String, String, String> {
    
        public CallAPI(){
            //set context variables if required
        }
    
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
    
         @Override
         protected String doInBackground(String... params) {
            String urlString = params[0]; // URL to call
            String data = params[1]; //data to post
            OutputStream out = null;

            try {
                URL url = new URL(urlString);
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                out = new BufferedOutputStream(urlConnection.getOutputStream());

                BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(out, "UTF-8"));
                writer.write(data);
                writer.flush();
                writer.close();
                out.close();

                urlConnection.connect();
            } catch (Exception e) {
                System.out.println(e.getMessage());
            }
        }
    }

References:

• https://developer.android.com/reference/java/net/HttpURLConnection.html
• How to add parameters to HttpURLConnection using POST using NameValuePair

Original Answer (May 2010)

Note: This solution is outdated. It only works on Android devices up to 5.1. Android 6.0 and above do not include the Apache http client used in this answer.

Http Client from Apache Commons is the way to go. It is already included in android. Here's a simple example of how to do HTTP Post using it.

public void postData() {
    // Create a new HttpClient and Post Header
    HttpClient httpclient = new DefaultHttpClient();
    HttpPost httppost = new HttpPost("http://www.yoursite.com/script.php");

    try {
        // Add your data
        List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(2);
        nameValuePairs.add(new BasicNameValuePair("id", "12345"));
        nameValuePairs.add(new BasicNameValuePair("stringdata", "Hi"));
        httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));

        // Execute HTTP Post Request
        HttpResponse response = httpclient.execute(httppost);
        
    } catch (ClientProtocolException e) {
        // TODO Auto-generated catch block
    } catch (IOException e) {
        // TODO Auto-generated catch block
    }
}