How to call a RESTful Method from Android? - multithreading

Question

I've tried two different ways to call a simple REST method from Android; said REST method - which works from other clients - simply returns an int val such as 17.
Both of the following attempts were based on code I found online. One is like so:
public void onFetchBtnClicked(View v){
if(v.getId() == R.id.FetchBtn){
Toast.makeText(getApplicationContext(), "You mashed the button, dude.", Toast.LENGTH_SHORT).show();
new NetworkTask().execute();
}
}
public static class NetworkTask extends AsyncTask {
#Override
protected String doInBackground(Void... params) {
final String TAG;
TAG = "callWebService";
String deviceId = "Android Device";
HttpClient httpclient = new DefaultHttpClient();
HttpGet request = new HttpGet("http://localhost:28642/api/Departments/GetCount");
request.addHeader("deviceId", deviceId);
ResponseHandler<String> handler = new BasicResponseHandler();
String result = "";
try
{
result = httpclient.execute(request, handler);
}
catch (ClientProtocolException e)
{
e.printStackTrace();
Log.e(TAG, "ClientProtocolException in callWebService(). " + e.getMessage());
}
catch (IOException e)
{
e.printStackTrace();
Log.e(TAG, "IOException in callWebService(). " + e.getMessage());
}
httpclient.getConnectionManager().shutdown();
Log.i(TAG, "**callWebService() successful. Result: **");
Log.i(TAG, result);
Log.i(TAG, "*****************************************");
return result;
}
#Override
protected void onPostExecute(String result) {
final String TAG;
TAG = "onPostExecute";
if (null != result)
Log.i(TAG, result);
}
With the code above, after the following line of code fails:
result = httpclient.execute(request, handler) ;
...I get, "*E/callWebService﹕ IOException in callWebService(). Connection to http://localhost:28642 refused*"
This problem may be a threading issue, as I read this in O'Reilly's "Programming Android" book by Mednieks, Dornin, Meike, and Nakamura: "AsyncTask is a convenenient tool for running small, asynchronous tasks. Just remember that the doInBackground method runs on a different thread! It must not write any state visible from another thread or read any state writable from another thread. This includes its parameters."
With my other attempt:
public void onFetchBtnClicked(View v){
if(v.getId() == R.id.FetchBtn){
Toast.makeText(getApplicationContext(), "You mashed the button, dude.", Toast.LENGTH_SHORT).show();
callWebService("http://localhost:28642/api/Departments/GetCount");
}
}
public String callWebService(String requestUrl)
{
final String TAG;
TAG = "callWebService";
String deviceId = "Android Device";
HttpClient httpclient = new DefaultHttpClient();
HttpGet request = new HttpGet(requestUrl);
request.addHeader("deviceId", deviceId);
ResponseHandler<String> handler = new BasicResponseHandler();
String result = "";
try
{
result = httpclient.execute(request, handler);
}
catch (ClientProtocolException e)
{
e.printStackTrace();
Log.e(TAG, "ClientProtocolException in callWebService(). " + e.getMessage());
}
catch (IOException e)
{
e.printStackTrace();
Log.e(TAG, "IOException in callWebService(). " + e.getMessage());
}
httpclient.getConnectionManager().shutdown();
Log.i(TAG, "**callWebService() successful. Result: **");
Log.i(TAG, result);
Log.i(TAG, "*****************************************");
return result;
}
...the debugger dumps me into View.class after hitting that same problem line (result = httpclient.execute(request, handler)). Why it does that, I don't know*, but I think the crux of the problem, as indicated by err msgs in logcat, is: "Caused by: android.os.NetworkOnMainThreadException"
*Maybe because something untoward is being attempted within the UI (View) thread.
Also (not a big deal, but "interesting," perhaps): the Toast doesn't pop up when a method call is made after it (it works otherwise).
The (Web API) server has a breakpoint set in its corresponding Controller method, but it is never reached. As mentioned, the server is running, and responds just fine to other (Windows app) clients.
There must be a somewhat straightforward way of calling a RESTful method from Android. But what/how?
UPDATE
I tried this, now, too, calling it like so:
RestClient client = new RestClient("http://localhost:28642/api/Departments/GetCount");
try {
client.Execute(RestClient.RequestMethod.GET);
} catch (Exception e) {
e.printStackTrace();
}
String response = client.getResponse();
Log.i("CZECH_THIS", response);
...but it also is (or seems, anyway) happy to throw the "NetworkOnMainThread" exception.
UPDATE 2
This is the closest I've gotten so far, I think. Maybe the server is the culprit in this case, because with this code:
public void onFetchBtnClicked(View v){
if(v.getId() == R.id.FetchBtn){
Toast.makeText(getApplicationContext(), "You mashed the button, dude.", Toast.LENGTH_SHORT).show();
new CallAPI().execute("http://localhost:28642/api/Departments/GetCount");
}
}
public static class CallAPI extends AsyncTask<String, String, String> {
#Override
protected String doInBackground(String... params) {
String urlString=params[0]; // URL to call
String resultToDisplay = "";
InputStream in = null;
// HTTP Get
try {
URL url = new URL(urlString);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream());
} catch (Exception e ) {
System.out.println(e.getMessage());
return e.getMessage();
}
return resultToDisplay;
}
protected void onPostExecute(String result) {
Log.i("FromOnPostExecute", result);
}
} // end CallAPI
....the exception that is thrown is:
libcore.io.ErrnoException: connect failed: ECONNREFUSED (Connection refused)
failed to connect to localhost/127.0.0.1 (port 28642): connect failed: ECONNREFUSED (Connection refused)
...and the Android app continues to run (it falls over in the other examples).
Why is my server refusing the connection?
UPDATE 3
I thought for a minute I had it: I forgot to pass the serial Num with the URL. But even after doing so, it fails.
I have a breakpoint in the server app, in the Controller method; also, in the Repository method, but they are never reached.
What could be wrong?
Is "localhost" the wrong thing to use (in the URL)? Should I use the name of the computer instead?
Does the URL (passed literally as "http://localhost:28642/api/Departments/GetCount?serialNum=4242") need to be verbatimized?
UPDATE 4
Changing the "locohost" to the machine name, I get "No address associated with hostname" so that's not the problem...
Oddly, though, this line runs fine:
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
...whereas this is the last line before the exception is thrown/caught:
in = new BufferedInputStream(urlConnection.getInputStream());
Looking at this, though, perhaps I need to escape my whacks; but when you already have double-whacks, as in after "http:", do you have to do triple-whacks? Or quadruple whacks? Surely not ceiling wax...?

Answer 1

I've got it working now. There's an article about it here.
This is the code from there without any explanation:
public class MainActivity extends ActionBarActivity {
private GetDepartmentsCount _getDeptsCount;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button getDeptsCountBtn = (Button)findViewById(R.id.DeptsCountBtn);
getDeptsCountBtn.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
_getDeptsCount = new GetDepartmentsCount();
_getDeptsCount.execute("http://10.0.2.2:28642/api/Departments/GetCount?serialNum=4242");
}
});
}
#Override
public void onStop() {
super.onStop();
_getDeptsCount.cancel(true);
}
private class GetDepartmentsCount extends AsyncTask<String, String, String> {
#Override
protected String doInBackground(String... params) {
String urlString = params[0]; // URL to call
String result = "";
// HTTP Get
try {
URL url = new URL(urlString);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
if (null != inputStream)
result = IOUtils.toString(inputStream);
} catch (Exception e) {
System.out.println(e.getMessage());
return e.getMessage();
}
return result;
}
#Override
protected void onPostExecute(String result) {
EditText dynCount = (EditText)findViewById(R.id.dynamicCountEdit);
dynCount.setText(result + " records were found");
Log.i("FromOnPostExecute", result);
}
}
}