Android - POST to RESTful Web Service

Question

I am looking for some guidance on how to post data to a web service in my Android application. Unfortunately this is a school project, so I'm not able to use external libraries.

The web service has a base URL, for example:

http://example.com/service/create

And takes two variables, in the following format:

username = "user1"
locationname = "location1"

The web service is RESTful and uses an XML structure, if that makes a difference. From my research I understand I should be using URLconnection rather than the deprecated HTTPconnection, but I cannot find an example of what I am looking for.

Here is my attempt, which is currently not working:

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toPost test = new toPost();
        text.execute();
    }

    private class toPost extends AsyncTask<URL, Void, String> {
        @Override
        protected String doInBackground(URL... params) {
            HttpURLConnection conn = null;
            try {
                URL url = new URL("http://example.com/service");
                conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(10000);
                conn.setConnectTimeout(15000);
                conn.setRequestMethod("POST");
                conn.setDoInput(true);
                conn.setDoOutput(true);
                String body = "username=user1&locationname=location1";
                OutputStream output = new BufferedOutputStream(conn.getOutputStream());
                output.write(body.getBytes());
                output.flush();
            } catch (ProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                conn.disconnect();
            }
            return null;
        }
    }

}

Answer 1

My suggestion is to use Retrofit among with Jackson converter.

Retrofit supports both asynchronous and synchronous requests. It supports GET, POST, PUT, DELETE, and HEAD methods.

Jackson will help you to parse XML to JSON object.

Both of these are very easy to use and have good documentation.

Here you can find simple tutorial for using Retrofit.

Answer 2

try this. (msg is the xml string )

 try
      {
        URL url = new URL(address);
        URLConnection uc = url.openConnection();
        HttpURLConnection conn = (HttpURLConnection) uc;
        conn.setDoInput(true);
        conn.setDoOutput(true);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-type", "text/xml");        
        PrintWriter pw = new PrintWriter(conn.getOutputStream());
        pw.write(msg.getText());
        pw.close();
        BufferedInputStream bis = new BufferedInputStream(conn.getInputStream());
        bis.close();

      }
      catch (Exception e)
      {
        e.printStackTrace();
      }

Answer 3

You would have to commit the request. This can be done by calling getResponseCode(), or getResponseMessage()) or getInputStream() for the response to be returned and processed.

Working code for your example:

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import java.io.BufferedOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.ProtocolException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        toPost test = new toPost();
        test.execute();
    }

    private class toPost extends AsyncTask<URL, Void, String> {
        @Override
        protected String doInBackground(URL... params) {
            HttpURLConnection conn = null;
            try {
                URL url = new URL("http://example.com/service");
                conn = (HttpURLConnection) url.openConnection();
                conn.setReadTimeout(10000);
                conn.setConnectTimeout(15000);
                conn.setRequestMethod("POST");
                conn.setDoInput(true);
                conn.setDoOutput(true);
                String body = "username=user1&locationname=location1";
                OutputStream output = new BufferedOutputStream(conn.getOutputStream());
                output.write(body.getBytes());
                output.flush();

                //This is needed
                // Could alternatively use conn.getResponseMessage() or conn.getInputStream()
                conn.getResponseCode();

            } catch (ProtocolException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                conn.disconnect();
            }
            return null;
        }
    }
}

Answer 4

Yes, you should use URLConnection for making requests.

You can send xml data as a payload.

Please refer Android - Using HttpURLConnection to POST XML data

    URL url = new URL(url);
    HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    try {
        conn.setReadTimeout(10000);
        conn.setConnectTimeout(15000);
        conn.setRequestMethod("POST");
        conn.setDoInput(true);
        conn.setDoOutput(true);
        String body = "<xml...</xml>";
        OutputStream output = new BufferedOutputStream(conn.getOutputStream());
        output.write(body.getBytes());
        output.flush();
    } finally {
        conn.disconnect();
    }

Answer 5

If you want to use HttpUrlConnection, you can refer to the following two samples. Hope this helps!

private class LoginRequest extends AsyncTask<Void, Void, String> {

    @Override
    protected String doInBackground(Void... voids) {
        String address = "http://server/login";
        HttpURLConnection urlConnection;
        String requestBody;
        Uri.Builder builder = new Uri.Builder();
        Map<String, String> params = new HashMap<>();            
        params.put("username", "bnk");
        params.put("password", "bnk123");

        // encode parameters
        Iterator entries = params.entrySet().iterator();
        while (entries.hasNext()) {
            Map.Entry entry = (Map.Entry) entries.next();
            builder.appendQueryParameter(entry.getKey().toString(), entry.getValue().toString());
            entries.remove();
        }
        requestBody = builder.build().getEncodedQuery();

        try {
            URL url = new URL(address);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setDoOutput(true);
            urlConnection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
            OutputStream outputStream = new BufferedOutputStream(urlConnection.getOutputStream());
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outputStream, "utf-8"));
            writer.write(requestBody);
            writer.flush();
            writer.close();
            outputStream.close();

            JSONObject jsonObject = new JSONObject();
            InputStream inputStream;
            // get stream
            if (urlConnection.getResponseCode() < HttpURLConnection.HTTP_BAD_REQUEST) {
                inputStream = urlConnection.getInputStream();
            } else {
                inputStream = urlConnection.getErrorStream();
            }
            // parse stream
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String temp, response = "";
            while ((temp = bufferedReader.readLine()) != null) {
                response += temp;
            }
            // put into JSONObject
            jsonObject.put("Content", response);
            jsonObject.put("Message", urlConnection.getResponseMessage());
            jsonObject.put("Length", urlConnection.getContentLength());
            jsonObject.put("Type", urlConnection.getContentType());

            return jsonObject.toString();
        } catch (IOException | JSONException e) {
            return e.toString();
        }
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        Log.i(LOG_TAG, "POST\n" + result);
    }
}


private class JsonPostRequest extends AsyncTask<Void, Void, String> {

    @Override
    protected String doInBackground(Void... voids) {
        try {
            String address = "http://server/postvalue";
            JSONObject json = new JSONObject();                
            json.put("Title", "Dummy Title");
            json.put("Author", "Dummy Author");
            String requestBody = json.toString();
            URL url = new URL(address);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setDoOutput(true);
            urlConnection.setRequestProperty("Content-Type", "application/json");
            OutputStream outputStream = new BufferedOutputStream(urlConnection.getOutputStream());
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(outputStream, "utf-8"));
            writer.write(requestBody);
            writer.flush();
            writer.close();
            outputStream.close();

            InputStream inputStream;
            // get stream
            if (urlConnection.getResponseCode() < HttpURLConnection.HTTP_BAD_REQUEST) {
                inputStream = urlConnection.getInputStream();
            } else {
                inputStream = urlConnection.getErrorStream();
            }
            // parse stream
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
            String temp, response = "";
            while ((temp = bufferedReader.readLine()) != null) {
                response += temp;
            }
            // put into JSONObject
            JSONObject jsonObject = new JSONObject();
            jsonObject.put("Content", response);
            jsonObject.put("Message", urlConnection.getResponseMessage());
            jsonObject.put("Length", urlConnection.getContentLength());
            jsonObject.put("Type", urlConnection.getContentType());
            return jsonObject.toString();
        } catch (IOException | JSONException e) {
            return e.toString();
        }
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        Log.i(LOG_TAG, "POST RESPONSE: " + result);
        mTextView.setText(result);
    }
}

Answer 6

I would use the volley library, as suggested by google

Making a request is explained on that page, but is as simple as:

final TextView mTextView = (TextView) findViewById(R.id.text);
...

// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(this);
String url ="http://www.google.com";

// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
            new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        // Display the first 500 characters of the response string.
        mTextView.setText("Response is: "+ response.substring(0,500));
    }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        mTextView.setText("That didn't work!");
    }
});
// Add the request to the RequestQueue.
queue.add(stringRequest);