Question

I found an API for which I want to play as I am free. I want to ask if I want to develop Android app using the API and the API is HTTP protocol based (RESTful), how can I use the HTTPClient object to do so?

I have a general request info.

HEAD /authenticate/ HTTP/1.1
Host: my.api.com
Date: Thu, 17 Jul 2008 14:52:54 GMT
X-SE-Client: some-value
X-SE-Accept: xml
X-SE-Auth: 90a6d325e982f764f86a7e248edf6a660d4ee833

The response of the above would be if success.

HTTP/1.1 200 OK
Date: Thu, 17 Jul 2008 14:52:55 GMT
Server: MyApi
Content-Length: 795
Connection: close
Content-Type: text/xml

I know how to use HTTPClient to send HTTP requests but does it add extra headers and other unnecessary stuff to the request? How can I see the request made by HTTPClient object? I want to simply request passing text like in telnet.

Answer 1

You should be able to use HttpClient in Android to do what you need. I just finished the first part of an integration of Android with an ASP.NET MVC 3 site and I must say – it was quite painless. I use Json as my data exchange format.

You can view exactly what the header looks like by setting a debug point after building your request. Here is some sample code (please remember it is just sample code – not a full implementation).

This class is called by a separate thread than the UI thread:

public class RemoteDBAdapter {


    public String register(String email, String password) throws Exception
    {
        RestClient c = new RestClient("http://myurl/Account/Register");
        c.AddHeader("Accept", "application/json");
        c.AddHeader("Content-type", "application/json");
        c.AddParam("Email", email);
        c.AddParam("Password", password);

        c.Execute(RequestMethod.POST);

        JSONObject key = new JSONObject(c.getResponse());

        return key.getString("status");


    }

}

Use this class to build your request and execute it:

public class RestClient {

    public enum RequestMethod {
        GET,
        POST
    }

    private ArrayList <NameValuePair> params;
    private ArrayList <NameValuePair> headers;

    private String url;

    private int responseCode;
    private String message;

    private String response;

    public String getResponse() {
        return response;
    }

    public String getErrorMessage() {
        return message;
    }

    public int getResponseCode() {
        return responseCode;
    }

    public RestClient(String url)
    {
        this.url = url;
        params = new ArrayList<NameValuePair>();
        headers = new ArrayList<NameValuePair>();
    }

    public void AddParam(String name, String value)
    {
        params.add(new BasicNameValuePair(name, value));
    }

    public void AddHeader(String name, String value)
    {
        headers.add(new BasicNameValuePair(name, value));
    }

    public void Execute(RequestMethod method) throws Exception
    {
        switch(method) {
            case GET:
            {
                //add parameters
                String combinedParams = "";
                if(!params.isEmpty()){
                    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
                for(NameValuePair h : headers)
                {
                    request.addHeader(h.getName(), h.getValue());
                }

                executeRequest(request, url);
                break;
            }
            case POST:
            {
                HttpPost request = new HttpPost(url);

                //add headers
                for(NameValuePair h : headers)
                {
                    request.addHeader(h.getName(), h.getValue());
                }
                JSONObject jo = new JSONObject();


                if(!params.isEmpty()){
                    for (int i = 0; i < params.size();i++)
                    {
                        jo.put(params.get(i).getName(),params.get(i).getValue());


                    }
                    StringEntity se = new StringEntity(jo.toString());
                    se.setContentType("text/xml"); 
                    se.setContentEncoding( new BasicHeader(HTTP.CONTENT_TYPE, "application/json")); 

                    request.setEntity(se);
                    //request.setEntity(new UrlEncodedFormEntity(params, HTTP.UTF_8));
                }

                executeRequest(request, url);
                break;
            }
        }
    }

    private void executeRequest(HttpUriRequest request, String url)
    {
        //HttpClient client = new DefaultHttpClient();
        HttpClient client = HttpClientFactory.getThreadSafeClient();

        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);

                // Closing the input stream will trigger connection release
                instream.close();
            }

        } catch (ClientProtocolException e)  {
            client.getConnectionManager().shutdown();
            e.printStackTrace();
        } catch (IOException e) {
            client.getConnectionManager().shutdown();
            e.printStackTrace();
        }
    }

    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");
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return sb.toString();
    }
}

EDIT:

Oh ya and the HttpClientFactory:

// Should be thread safe
public class HttpClientFactory {

            private static DefaultHttpClient client;

            public synchronized static DefaultHttpClient getThreadSafeClient() {
                    if (client != null)
                            return client;
                    client = new DefaultHttpClient();
                    ClientConnectionManager mgr = client.getConnectionManager();
                    HttpParams params = client.getParams();
                    client = new DefaultHttpClient(new ThreadSafeClientConnManager(params,
                                    mgr.getSchemeRegistry()), params);
                return client;

            }
    }