Android WCF REST requests made simple (using JSON)

I’ve been struggling for some time trying to get my Android phone to talk with a WCF REST web service. Finally I was able to do it and I decided to share the knowledge.

A few things to consider first:

1. I gave up trying to make it work using XML but I like JSON anyway. If you manage to get this working using xml headers please comment !
2. The response is not even ready yet, I just got excited I got this working. I’ll post an update later doing a JSON parsing of the response.
3. The C# WCF REST web service was built using the Online Pattern and not the default one: new project –> online templates –> WCF –> WCF REST Service Template 40(CS)
4. The Operation Contracts are tagged to use JSON:

   [OperationContract]
   [WebInvoke(UriTemplate = "ValidateCredentials",
       BodyStyle = WebMessageBodyStyle.Wrapped,
       Method = "POST",
       RequestFormat = System.ServiceModel.Web.WebMessageFormat.Json)]
   string ValidateCredentials(string username, string password);

About the Android code:

I want to stress that this is just a quick example of how I made it work, avoid making comments about the quality of the code please !

Notice I’ve obscured the IP address and port. Change that to suit your needs.

Also, I’m using a singleton pattern, you can avoid that too if you want to.

import java.io.IOException;

import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.HttpConnectionParams;
import org.json.JSONException;
import org.json.JSONObject;

public final class RestClient {

private static final String URL = “http://XXX.XXX.XXX.XXX:YYYY/AccountServices/ValidateCredentials”;

private static RestClient instance = new RestClient();

public static RestClient getInstance() {
return instance;
}

private RestClient() {

}

public JSONObject sendJson(ArrayList<NameValuePair> params) {
JSONObject result = null;

HttpClient client = new DefaultHttpClient();
HttpConnectionParams.setConnectionTimeout(client.getParams(), 10000);
HttpResponse response;

JSONObject json = new JSONObject();

try {
HttpPost post = new HttpPost(URL);

for (NameValuePair p : params){
json.put(p.getName(), p.getValue());
}

StringEntity se = new StringEntity(json.toString());

post.setEntity(se);
post.setHeader(“Accept”, “application/json”);
post.setHeader(“Content-type”, “application/json”);
response = client.execute(post);
/* Checking response */
if (response != null) {
InputStream in = response.getEntity().getContent();
}
} catch (JSONException ex) {

} catch (UnsupportedEncodingException ex) {

} catch (ClientProtocolException ex) {

} catch (IOException ex) {

}

return result;
}

}

The problem I originally had were the headers ! I was getting “bad request” all the time. Seems the process of setting the headers on the HttpPost object is very precise.

To finish the example, this is how you make a call:

ArrayList<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("username", "username value"));
params.add(new BasicNameValuePair("password", "password value"));

RestClient.getInstance().sendJson(params);

The ideal scenario should be to have an URL as a parameter too. I’ll add that on a second update regarding this topic.

Again, I’m not doing anything with the response !!! Actually I don’t even know how I’ll work that out, but should be fairy simple from here.

Bests,

Angel

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