How to call a RESTful web service from Android?

This is an sample restclient class

public class RestClient{    public enum RequestMethod    {        GET,        POST    }    public int responseCode=0;    public String message;    public String response;    public void Execute(RequestMethod method,String url,ArrayList<NameValuePair> headers,ArrayList<NameValuePair> params) throws Exception    {        switch (method)        {            case GET:            {                // add parameters                String combinedParams = "";                if (params!=null)                {                    combinedParams += "?";                    for (NameValuePair p : params)                    {                        String paramString = p.getName() + "=" + URLEncoder.encode(p.getValue(),"UTF-8");                        if (combinedParams.length() > 1)                            combinedParams += "&" + paramString;                        else                            combinedParams += paramString;                    }                }                HttpGet request = new HttpGet(url + combinedParams);                // add headers                if (headers!=null)                {                    headers=addCommonHeaderField(headers);                    for (NameValuePair h : headers)                        request.addHeader(h.getName(), h.getValue());                }                executeRequest(request, url);                break;            }            case POST:            {                HttpPost request = new HttpPost(url);                // add headers                if (headers!=null)                {                    headers=addCommonHeaderField(headers);                    for (NameValuePair h : headers)                        request.addHeader(h.getName(), h.getValue());                }                if (params!=null)                    request.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));                executeRequest(request, url);                break;            }        }    }    private ArrayList<NameValuePair> addCommonHeaderField(ArrayList<NameValuePair> _header)    {        _header.add(new BasicNameValuePair("Content-Type","application/x-www-form-urlencoded"));        return _header;    }    private void executeRequest(HttpUriRequest request, String url)    {        HttpClient client = new DefaultHttpClient();        HttpResponse httpResponse;        try        {            httpResponse = client.execute(request);            responseCode = httpResponse.getStatusLine().getStatusCode();            message = httpResponse.getStatusLine().getReasonPhrase();            HttpEntity entity = httpResponse.getEntity();            if (entity != null)            {                InputStream instream = entity.getContent();                response = convertStreamToString(instream);                instream.close();            }        }        catch (Exception e)        { }    }    private static String convertStreamToString(InputStream is)    {        BufferedReader reader = new BufferedReader(new InputStreamReader(is));        StringBuilder sb = new StringBuilder();        String line = null;        try        {            while ((line = reader.readLine()) != null)            {                sb.append(line + "\n");            }            is.close();        }        catch (IOException e)        { }        return sb.toString();    }}

Recently discovered that a third party library - Square Retrofit can do the job very well.

Defining REST endpoint

public interface GitHubService {   @GET("/users/{user}/repos")   List<Repo> listRepos(@Path("user") String user,Callback<List<User>> cb);}

Getting the concrete service

RestAdapter restAdapter = new RestAdapter.Builder()    .setEndpoint("https://api.github.com")    .build();GitHubService service = restAdapter.create(GitHubService.class);

Calling the REST endpoint

List<Repo> repos = service.listRepos("octocat",new Callback<List<User>>() {     @Override    public void failure(final RetrofitError error) {        android.util.Log.i("example", "Error, body: " + error.getBody().toString());    }    @Override    public void success(List<User> users, Response response) {        // Do something with the List of Users object returned        // you may populate your adapter here    }});

The library handles the json serialization and deserailization for you. You may customize the serialization and deserialization too.

Gson gson = new GsonBuilder()    .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)    .registerTypeAdapter(Date.class, new DateTypeAdapter())    .create();RestAdapter restAdapter = new RestAdapter.Builder()    .setEndpoint("https://api.github.com")    .setConverter(new GsonConverter(gson))    .build();

Stop with whatever you were doing ! :)

Implement the RESTful client as a SERVICE and delegate the intensive network stuff to activity independent component: a SERVICE.

Watch this insightful videohttp://www.youtube.com/watch?v=xHXn3Kg2IQE where Virgil Dobjanschi is explaining his approach(es) to this challenge...