Develop Reference

Android: how can I make an HTTP HEAD request?

I would like to make a simple HTTP HEAD request, without keep-alive.
How can I do that in Android?

using HttpClient:
As njzk2 suggested, with HttpClient() it's very straightforward:
HttpResponse response = new HttpClient().execute(new HttpHead(myUrl));
However there is a problem with not being able to close the connection. Usually on the HttpClient, you would get the entity using:
HttpEntity entity = response.getEntity();
and then you would get the input stream from the entity
InputStream instream = entity.getContent();
...
instream.close();
and by closing the input stream, the connection would close.
However, in the case of a HEAD request, the entity appears to be null (possibly because HEAD requests don't return the body in the response), so the input stream cannot be fetched and closed and the connection doesn't close either.
In the last edit to his answer, njzk2 is suggesting to use AndroidHttpClient, which is a more recent implementation (API 8) of HttpClient and it actually has a close() method. I haven't used it but I guess it will work fine. However, as the Android development team suggests, the HttpUrlConnection should be the preferred Android client to use.
using HttpUrlConnection:
Actually it seems quite easy to make HEAD requests using HttpUrlConnection and make sure that the connection closes:
HttpURLConnection urlConnection = null;
System.setProperty("http.keepAlive", "false");
try {
URL url = new URL(stringUrl);
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("HEAD");
urlConnection.getInputStream().close();
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}

Trivially :
HttpResponse response = new AndroidHttpClient().execute(new HttpHead(myUrl));
Typically you'll use the same AndroidHttpClient for several connections, then call close on it.

For ordinary Java and Android
I am using some standard Java code to test the existence of a resource and in the same time to check whether a resource has been changed, provided the parameter if_modified_since is non-zero.
URL url = new URL(adr);
try {
URLConnection con = url.openConnection();
con.setIfModifiedSince(if_modified_since);
if (con instanceof HttpURLConnection) {
/* Workaround for https://code.google.com/p/android/issues/detail?id=61013 */
con.addRequestProperty("Accept-Encoding", "identity");
((HttpURLConnection) con).setRequestMethod("HEAD");
int response = ((HttpURLConnection) con).getResponseCode();
if (response == HttpURLConnection.HTTP_UNAVAILABLE)
return false;
if (response == HttpURLConnection.HTTP_NOT_MODIFIED)
return false;
}
if (if_modified_since != 0) {
long modified = OpenOpts.getLastModified(con);
if (modified != 0 && if_modified_since >= modified)
return false;
}
InputStream in = con.getInputStream();
in.close();
return true;
} catch (FileNotFoundException x) {
return false;
} catch (UnknownHostException x) {
return false;
} catch (SocketException x) {
return false;
}
Interestingly the code needs a con.getInputStream() and I don't get some errors here. But I needed some helper code, to also cater for URIs that point to JARs. The helper code is:
private static long getLastModified(URLConnection con)
throws IOException {
if (con instanceof JarURLConnection) {
return ((JarURLConnection) con).getJarEntry().getTime();
} else {
return con.getLastModified();
}
}
The code can be further optimized by some specialization if the
URI is schema file: , one can then directly do File.exists() and File.getLastModified().
We do not throw a ServiceUnvailable exception here, we basically assume that the outer code would catch an IOException and then assume a false
result of the getHead().

How to disconnect an HttpUrlConnection on HTC (Froyo and below) phones?

I need to disconnect a long polling http request from the client side in some cases. The relevant part of the HttpUrlConnection I make to the server is as follows (all the code below is within a Thread's run() method):
try {
URL url = new URL(requestURL);
connection = (HttpURLConnection) url.openConnection();
connection.setRequestProperty("Accept-Charset", "UTF-8");
connection.setConnectTimeout(5 * 1000);
connection.setReadTimeout(60 * 1000);
connection.setRequestMethod("GET");
// read the output from the server
reader = new BufferedReader(new InputStreamReader(connection.getInputStream()));
StringBuilder stringBuilder = new StringBuilder();
String line = null;
while ((line = reader.readLine()) != null) {
stringBuilder.append(line + "\n");
}
Log.d(TAG, stringBuilder);
} catch (IOException ioe) {
Log.e(TAG, ioe);
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}
This is how I first initiate, then (after a second delay) try to cancel the request:
pollThread = new PollThread();
pollThread.start();
Log.d(TAG, "pollThread started");
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
pollThread.cancelRequest();
Log.d(TAG, "pollThread presumably cancelled");
}
}, 1000);
And this is what the cancelRequest() method looks like:
public void cancelRequest() {
if (connection != null) {
connection.disconnect();
}
}
So essentially,
I initiate a HttpUrlConnection with a get request, with 1 minute read timeout
Then after one second, I try to cancel the earlier request
The expected outcome is that the connection should throw an IOException when I call connection.disconnect()
And this is exactly what happens on various emulators (2.2 - 4.0.3), a Motorola Atrix (2.3.7) and a Samsung Note (4.0.1). But on some HTC devices running 2.2, the request will stay alive and it will recieve the response, despite the fact that I explicitly terminated the connection. I verified this with an HTC Desire and an HTC Wildfire.
What's going on here? How can I cancel such a request safely on all devices running 2.2+?
For your convenience, the whole code is available here, should you like to do a test drive yourself: https://gist.github.com/3306225

What's going on here?
This is a known bug in earlier android release (Froyo 2.2) which, in sort, sockets can not be closed asynchronously by other threads, and has been fixed in Gingerbread 2.3:
Issue 11705: impossible to close HTTP connection using HttpURLConnection
How can I cancel such a request safely on all devices running 2.2+?
Comments from project member in that link:
The best approximation of this that will work in current releases is to set read and connect timeouts on the HTTP connection.
Hope that helps.

Actually, I would recommend you to use Apache HttpClient lib, instead of the default supplied with android.
You can download it from: http://code.google.com/p/httpclientandroidlib/
If you want to go "all the way", you can also use AndroidHttpClient "that is configured with reasonable default settings and registered schemes for Android" and could also support cookies. You can download it from here (I can't remember when I found the original one...)
This is how you use a "Get" call, I guess you can figure out the rest:
InputStream isResponse = null;
HttpGet httpget = new HttpGet(strUrl);
HttpResponse response = getHttpClient().execute(httpget);
HttpEntity entity = response.getEntity();
isResponse = entity.getContent();
responseBody = convertStreamToString(isResponse);
and
/**
* #return the mClient
*/
protected AndroidHttpClient getHttpClient() {
if (mClient == null)
mClient = AndroidHttpClient.newInstance(mCookieStore);
return mClient;
}
To close the connction:
getHttpClient().close();

Android HTTP Client freezes

I'm experiencing some odd behavior in my HTTP requests. I have some users that are saying that this call isn't ever coming back (the spinner marking it's asynchronous call never goes away). I have seen this happen before, but I attributed it to the emulator going through Charles Proxy. I haven't yet seen it on actual phone until now.
I'm not sure what would cause this to happen, which is why I'm posting it here. Here's the call, using Jackson to deserialize the result into a Value Object. The two spots I saw the emulator freeze are httpclient.execute(httpGet); and getObjectMapper().readValue(jp, SyncVO.class);.
While debugging, stepping over the offending statement caused the debugger to never gain control back of stepping. Meanwhile, I see the request go out AND come back from the server through Charles. It's just that the app doesn't seem to get the response and just sits there.
So, here's the code. Thanks for any help!
public SyncVO sync(String userId, long lastUpdate, boolean includeFetch) throws IOException {
SyncVO result = null;
String url = BASE_URL + "users/" + userId + "/sync" + "?" + "fetch=" + includeFetch;
if (lastUpdate > 0) {
url += "&updatedSince=" + lastUpdate;
}
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpGet httpGet = new HttpGet(url);
httpGet.setHeader("Accept", "application/json");
httpGet.setHeader("Accept-Encoding", "gzip");
httpGet.setHeader(AUTHORIZATION, BEARER + " " + mOAuthToken);
httpclient.getParams().setParameter(CoreProtocolPNames.USER_AGENT, USER_AGENT_STRING);
httpclient.getParams().setBooleanParameter(CoreProtocolPNames.USE_EXPECT_CONTINUE, false);
HttpResponse response = httpclient.execute(httpGet);
if (isUnauthorized(response)) {
APPLICATION.needReauthentication();
return null;
}
if (response != null) {
InputStream stream = response.getEntity().getContent();
Header contentEncoding = response.getFirstHeader("Content-Encoding");
if (contentEncoding != null && contentEncoding.getValue().equalsIgnoreCase("gzip")) {
stream = new GZIPInputStream(stream);
}
InputStreamReader inReader = new InputStreamReader(stream, "UTF-8");
JsonParser jp = mJsonFactory.createJsonParser(inReader);
result = getObjectMapper().readValue(jp, SyncVO.class);
}
return result;
}
private ObjectMapper getObjectMapper() {
return (new ObjectMapper()
.configure(Feature.AUTO_DETECT_FIELDS, true)
.configure(Feature.FAIL_ON_UNKNOWN_PROPERTIES, false)
.configure(JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS, true));
}

don't forget to consume entities content after each request.
HttpEntity entity = response.getEntity();
try {
if (entity != null)
entity.consumeContent();
} catch (IOException e) {
e.printStackTrace();
}

You should definitely use connection timeout and socket read and be prepared for the worst from the server. Network operations will never be 100% predictable and there is not much your client can do then so make sure you code optimally.
httpParameters = httpclient.getParams();
HttpConnectionParams.setConnectionTimeout(httpParameters, 5000);
HttpConnectionParams.setSoTimeout(httpParameters, 10000);
You can also cancel a task with asyncTask.cancel(true);

The reason is because you have left stream open. As such, the response is left in limbo. This means your global variable httpClient is also left in limbo, and unable to get a new entity when it re-uses the client.
You should call close() after finishing with the stream.
stream.close();

Network calls take a while and will block the UI thread. Same with your jackson deserialization code. This stuff needs to be put on a separate thread. See AsyncTask for an easy way to do it.

How to use HTTP cookies in an Android app?

I am trying to maintain a logged-in user session between my Android app and my Drupal website. In my research, it comes down to sending cookie(s) back to Drupal but I am struggling to implement it. How can I make a start on this?

Just in case anyone else got the same issue, I had similar problem and I was able to solve it by the following code:
1- Define CookieManager and CookieStore in your class
CookieManager cookieManager;
CookieStore cookieStore;
2- Add default cookie handler, e.g. in the class constructor or in OnCreate method
cookieManager = new CookieManager();
CookieHandler.setDefault(cookieManager);
3- Use the cookie storage when you do HTTP request
public byte[] openURI(String uri) {
try {
URI uriObj = new URI(uri);
DefaultHttpClient client = new DefaultHttpClient();
// Use the cookieStor with the request
if (cookieStore == null) {
cookieStore = client.getCookieStore();
} else {
client.setCookieStore(cookieStore);
}
HttpGet getRequest = new HttpGet(uriObj);
HttpResponse response = client.execute(getRequest);
// Read the response data
InputStream instream = response.getEntity().getContent();
int contentLength = (int) response.getEntity().getContentLength();
byte[] data = new byte[contentLength];
instream.read(data);
response.getEntity().consumeContent();
return data ;
} catch (URISyntaxException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}

I am pretty sure that if you use the HttpClient provided with the Android APIs it should do session management with cookies for you until you close the connection manually.
If I am wrong on this, then you can easily work around this by implementing your own cookie store using the CookieStore interface or the BasicCookieStore class. If all else fails, you can store cookies manually and set cookies in the header each time you make a HTTP request.
I am not sure how this might change for your particular problem though but this should most likely work considering the description of the problem you gave.

How to improve my Rest Calls on Android?

I am making an app for Android. I like to make the rest calls as quick as possible. When I get my results as XML it takes 5 seconds (!) to get a simple xml like this:
<souvenirs>
<souvenir>
<id>1</id>
<name>Example 1</name>
<rating>3.4</rating>
<photourl>/images/example.jpg</photourl>
<price>3.50</price>
</souvenir>
<souvenir>
<id>2</id>
<name>Example 2</name>
<rating>2.4</rating>
<photourl>/images/example.jpg</photourl>
<price>8.50</price>
</souvenir>
</souvenirs>
So I tried it with JSON. But that takes also about 5 seconds to retrieve.
I load the XML in android with the following code:
URL url = new URL("http://example.nu?method=getAllSouvenirs");
URLConnection conn = url.openConnection();
long t=System.currentTimeMillis();
InputStream ins = conn.getInputStream();
Log.d("info", String.valueOf((System.currentTimeMillis()-t)));
The log says it takes about 5000 ms to get the inputstream.. Is there any way to speed this up? does anybody knows which technique the Android Market uses? This loads way faster than my app..
Thanks in advance! :)

When you try to get the data "manually" - via browser or via other means (wget, curl) how long does it take there.
On Android you also should take the mobile network into consideration that is usually significantly slower than for a desktop computer. Also latencies are bigger.
To me this sounds a lot like issues in the backend (e.g. trying to resolve the IP of the client and thus taking lots of time).

use Apache HttpClient instead of URLConnection:
Apache http client or URLConnection
EDIT(2012-02-07): no longer true on newer android platform please read: http://android-developers.blogspot.com/2011/09/androids-http-clients.html

Maybe that is how it is implemented and you can't do nothing. That is my guess.
My opinion is to do all connection based stuff on your own thread (to put in in background) and in foreground (main UI thread) entertain user. :)
I have played a little bit around this and it works fast enough for me... Here is my code:
private static HttpResponse doPost(String url, JSONStringer json) {
try {
HttpPost request = new HttpPost(url);
StringEntity entity;
entity = new StringEntity(json.toString());
entity.setContentType("application/json;charset=UTF-8");
entity.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE, "application/json;charset=UTF-8"));
request.setEntity(entity);
try {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpResponse response = httpClient.execute(request);
return response;
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return null;
}
And somewhere else I call that method like:
HttpResponse httpResponse = doPost(url, json);
BufferedReader reader = new BufferedReader(new InputStreamReader(httpResponse.getEntity().getContent(), "UTF-8"));
It works fine for me...