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Parse REST API, Validate User session

I am using Parse REST API for a game, altough there are java libraries for Parse I would like to handle the transfer protocolls my self using java.net for learning purposes. Please look away from things like, why dont I use Apache HttpClient.
Following the Parse REST API Guide
Here is what I am trying to achive:
Signup
User Login
validating session tokens / Retriving current user
The first two steps works just fine, the former using POST request method and the latter using GET with some paramaters.
Keeping the Request and Response format in mind I also provide the Application-ID and the REST-API-Key which are the appropriate request headers needed.
Now, for the third step using GET request with no paramaters, but with an additional header, the API expects there to be a Session-Token provided.
Code
private static void validateSessionToken(String token) throws IOException {
System.out.println("Token: " + token);
URL url = new URL("https://api.parse.com/1/users/me");
HttpsURLConnection con = (HttpsURLConnection) url.openConnection();
con.setRequestMethod("GET");
con.setRequestProperty("X-Parse-Application-Id", "xxxxxxx");
con.setRequestProperty("X-Parse-REST-API-Key", "xxxxxxxx");
con.setRequestProperty("X-Parse-Session-Token", token);
con.setRequestProperty("content-type", "application/json");
int responseCode = con.getResponseCode();
System.out.println("\nSending 'GET' request to URL : " + url);
System.out.println("Response Code : " + responseCode);
if(responseCode == 400) {
System.out.println("Bad request!");
return;
}
BufferedReader in = new BufferedReader(
new InputStreamReader(con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
in.close();
System.out.println(response.toString());
}
Outputs
Sending 'GET' request to URL : https://api.parse.com/1/users/me
Response Code : 400
Bad request!
Debugging
I have been using the PARSE API CONSOLE and Chrome network debugging tool to try and see what the difference is, but cannot see any.
From wiki:
400 Bad Request
The server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing)
Some photos that may help

So when I asked my JsonObject for the session token:
jsonObject.get("sessionToken").toString();
It returned: "r:WzB7qdmhkcW5qd2moM8gbBLDp" in quotation, but using:
jsonObject.get("sessionToken").getAsString();
it returned: r:WzB7qdmhkcW5qd2moM8gbBLDp
I was so focused on the request I did not even notice...

HttpUrlConnection: Cookies Show in CookieStore but not in the POST Header

In the code below I am running a post request on a website. What I dont understand is why the cookie shows up via the cookiemanager, but it does not show up in the POST header. See my comments in the code.
Can someone kindly explain what I am missing?
CookieManager cm = new CookieManager(null, CookiePolicy.ACCEPT_ALL);
CookieHandler.setDefault(cm);
...
connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
OutputStream outputStream = connection.getOutputStream();
outputStream.write(urlParams.getBytes(charset));
// Clear cookies to prove they are not from an old request.
cm.getCookieStore().removeAll();
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK)
throw new Exception("Invalid response code.");
// No cookie prints here:
Log.d("Aero", connection.getHeaderFields().toString());
List<HttpCookie> cookies = cm.getCookieStore().getCookies();
for (HttpCookie cookie : cookies) {
if (cookie.getName().equals("ASP.NET_SessionId")) {
// But we do get a cookie here
Log.d("Aero", cookie.toString());
}
}

Ok with a clear head this morning I have managed to solve this one myself. The problem was that the response was a 302 redirect and the redirected page had no cookie in the response header.
I needed to use:
connection.setInstanceFollowRedirects(false);
To ensure I was reading the response from the original header not the redirected one.

Not getting the right header response code with HttpUrlConnection

I have a simple situation.
Given one URL, the server header response code will be HTTP 200.
Now I'm trying it with another URL where the server FIRST responded with HTTP 302 (Found) and THEN redirects and responded with the header HTTP 200 code.
Hence, in second case, why connection.getResponseCode() does not return HTTP 302 and instead directly returns HTTP 200. I'm actually interested in checking the header response within the initial HTTP 302 response.
Here's the simplified HttpUrlConnection code (almost a carbon copy of many open-source implementations).
private int responseCode;
private Map<String, List<String>> headerFields;
public String getString(String url)
{
String response = null;
try
{
URL mUrl = new URL(url);
HttpURLConnection connection = (HttpURLConnection) mUrl.openConnection();
connection.setRequestMethod("GET");
responseCode = connection.getResponseCode();
headerFields = connection.getHeaderFields();
/* boilerplate buffered reader stuffs for getting stream + StringBuilder etc etc.*/
}
finally
{
connection.disconnect();
}
return response;
}
Extra info: The HTTP 302 contains the header key: 'location', though as expected, connection.getheaderFields() does not contain it.

You can configure whether redirects are automatically followed; see http://docs.oracle.com/javase/7/docs/api/java/net/HttpURLConnection.html#setFollowRedirects%28boolean%29.

Java function to detect valid webpage

I am trying to write a Java program that will load pages pointed to by valid links and report other links as broken. My problem is that the Java URL will download the appropriate page if the url is valid, and the search-engine results for the url if the url is invalid.
Is there a Java function that detects if the url resolves to a legitimate page . . . thanks very much,
Joel

HttpURLConnection#getResponseCode will give you an HTTP status code

You can get the HTTP response code for a URL like so:
public static int getResponseCode(URL url) throws IOException {
URLConnection conn = url.openConnection();
if (!(conn instanceof HttpURLConnection)) {
throw new IllegalArgumentException("not an HTTP url: " + url);
}
HttpURLConnection httpConn = (HttpURLConnection) conn;
return httpConn.getResponseCode();
}
Now the question is, what do you consider a "valid" webpage? For me, if a URL parses correctly and it's protocol is "http" (or https) and it's response code is in the 200 block or 302 (Found/Redirect) or 304 (Not modified), then it's valid:
public boolean isValidHttpResponseCode(int code) {
return ((code / 100) == 2) || (code == 302) || (code == 304);
}

Quickest way to get content type

I need to chech for the content type (if it's image, audio or video) of an url which has been inserted by the user. I have a code like this:
URL url = new URL(urlname);
URLConnection connection = url.openConnection();
connection.connect();
String contentType = connection.getContentType();
I'm getting the content type, but the problem is that it seems that it is necessary to download the whole file to check it's content type. So it last too much time when the file is quite big. I need to use it in a Google App Engine aplication so the requests are limited to 30 seconds.
Is there any other way to get the content type of a url without downloading the file (so it could be done quicker)?

Thanks to DaveHowes answer and googling around about how to get HEAD I got it in this way:
URL url = new URL(urlname);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("HEAD");
connection.connect();
String contentType = connection.getContentType();

If the "other" end supports it, could you use the HEAD HTTP method?

Be aware of redirects, I faced same problem with my remote content check.
Here is my fix:
/**
* Http HEAD Method to get URL content type
*
* #param urlString
* #return content type
* #throws IOException
*/
public static String getContentType(String urlString) throws IOException{
URL url = new URL(urlString);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("HEAD");
if (isRedirect(connection.getResponseCode())) {
String newUrl = connection.getHeaderField("Location"); // get redirect url from "location" header field
logger.warn("Original request URL: '{}' redirected to: '{}'", urlString, newUrl);
return getContentType(newUrl);
}
String contentType = connection.getContentType();
return contentType;
}
/**
* Check status code for redirects
*
* #param statusCode
* #return true if matched redirect group
*/
protected static boolean isRedirect(int statusCode) {
if (statusCode != HttpURLConnection.HTTP_OK) {
if (statusCode == HttpURLConnection.HTTP_MOVED_TEMP
|| statusCode == HttpURLConnection.HTTP_MOVED_PERM
|| statusCode == HttpURLConnection.HTTP_SEE_OTHER) {
return true;
}
}
return false;
}
You could also put some counter for maxRedirectCount to avoid infinite redirects loop - but this is not covered here. This is just a inspiration.

I faced a similar task where I needed to check the content type of the url, and the way how I managed it is with retrofit. First you have to define an endpoint to call it with the url you want to check:
#GET
suspend fun getContentType(#Url url: String): Response<Unit>
Then you call it like this to get the content type header:
api.getContentType(url).headers()["content-type"]