Reddit OAuth2 Java sample code (uses Google HTTP and json.org libs)

RedditOAuth.java

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import org.json.JSONObject;
import org.json.JSONTokener;

import com.google.api.client.extensions.appengine.http.UrlFetchTransport;
import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpContent;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestFactory;
import com.google.api.client.http.HttpRequestInitializer;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.UrlEncodedContent;

import com.google.appengine.api.utils.SystemProperty;

// Reddit's OAUTH docs are here:
// https://github.com/reddit/reddit/wiki/OAuth2
// http://www.reddit.com/r/redditdev/comments/218wd7/oauth_20_you_asked_i_listened_updated_and_more/ 


// Docs for Google HTTP lib, and GAE urlfetch:
// https://code.google.com/p/google-http-java-client/
// https://developers.google.com/appengine/docs/java/urlfetch/

// Apache License 
// copyright 2014 /u/redlist-admin

// You will need to comment out or replace my custom Log statements.

public class RedditOAuth {

    // This line is GAE specific!  for detecting when running on local admin
    public static final boolean production = (SystemProperty.Environment.Value.Production == SystemProperty.environment.value());

    public static final String OAUTH_API_DOMAIN = "https://oauth.reddit.com";

    // Step 1. Send user to auth URL
    public static final String OAUTH_AUTH_URL = "https://ssl.reddit.com/api/v1/authorize";
    // https://ssl.reddit.com/api/v1/authorize?client_id=CLIENT_ID&response_type=TYPE&state=RANDOM_STRING&redirect_uri=URI&duration=DURATION&scope=SCOPE_STRING

    // Step 2. Reddit sends user to REDIRECT_URI
    private static final String REDIRECT_URI = production ? <your app domain> + "/auth"
            : "http://127.0.0.1:8888/auth";

    // Step 3. Get token
    public static final String OAUTH_TOKEN_URL = "https://ssl.reddit.com/api/v1/access_token";

    // I think it is easier to create 2 reddit apps (one with 127.0.0.1 redirect URI)
    public static final String MY_APP_ID = production ? "???????????" : "???????";
    public static final String MY_APP_SECRET = production ? "??????????" : "???????";

    public static final String SCOPE_ID = "identity";

    // Field name in responses
    public static final String ACCESS_TOKEN_NAME = "access_token";
    public static final String REFRESH_TOKEN_NAME = "refresh_token";

    public static boolean permanentAccess = true;

    public static String getUserAuthUrl(String state) {
        String duration = permanentAccess ? "permanent" : "temporary";
        String url = OAUTH_AUTH_URL + "?client_id=" + MY_APP_ID + "&response_type=code&state=" + state
                + "&redirect_uri=" + REDIRECT_URI + "&duration=" + duration + "&scope=" + SCOPES;

        // scopes: modposts, identity, edit, flair, history, modconfig, modflair, modlog, modposts, modwiki,
        // mysubreddits, privatemessages, read, report, save, submit, subscribe, vote, wikiedit, wikiread, etc.
        return url;
    }

    // The Google Java HTTP library has a 'pluggable' architecture - the following line selects the URLFetch transport,
    // which is the native HTTP api for GAE.  'NetHttpTransport()' would be a more generic alternative.
    public static final HttpTransport HTTP_TRANSPORT = new UrlFetchTransport();
    
    // public static final JsonFactory JSON_FACTORY = new JacksonFactory();

    public static JSONObject getToken(String code) throws IOException {
        Log.v( "getToken for code=" + code );
        GenericUrl url = new GenericUrl(OAUTH_TOKEN_URL);
        Map<String, String> params = new HashMap<String, String>(3);
        params.put("grant_type", "authorization_code");
        params.put("code", code);
        params.put("redirect_uri", REDIRECT_URI);
        HttpContent hc = new UrlEncodedContent(params);

        HttpRequestFactory requestFactory = HTTP_TRANSPORT
                .createRequestFactory(new HttpRequestInitializer() {
                    @Override
                    public void initialize(HttpRequest request) {
                        // request.setParser( new JsonObjectParser(JSON_FACTORY) );
                        request.getHeaders().setBasicAuthentication(MY_APP_ID, MY_APP_SECRET);
                    }
                });

        HttpRequest request = requestFactory.buildPostRequest(url, hc);
        HttpResponse response = request.execute();

        JSONObject jo = null;
        try {
            if (response.isSuccessStatusCode()) {

                String json = response.parseAsString();
                Log.i("Success with " + json);

                // Parse with org.json
                JSONTokener tokener = null;
                tokener = new JSONTokener( json );
                jo = new JSONObject(tokener);

                // Sample response:
                // {"access_token": "cdkVPfKww5R0D1v-MJAD89Y19QM",
                // "token_type": "bearer",
                // "expires_in": 3600,
                // "refresh_token": "vzZ0PP0A4k-twzSuVyvRN7uH2JY",
                // "scope": "identity"}
            } else
                Log.w("Request failed with " + response.getStatusCode());
        } finally {
            response.disconnect();
        }

        return jo;
    }

    public static JSONObject refreshToken(String reftoke) throws IOException {
        Log.v( "refreshToken with reftoke=" + reftoke );
        GenericUrl url = new GenericUrl(OAUTH_TOKEN_URL);
        Map<String, String> params = new HashMap<String, String>(3);
        params.put("grant_type", "refresh_token");
        params.put("refresh_token", reftoke);
        HttpContent hc = new UrlEncodedContent(params);

        HttpRequestFactory requestFactory = HTTP_TRANSPORT
                .createRequestFactory(new HttpRequestInitializer() {
                    @Override
                    public void initialize(HttpRequest request) {
                        request.getHeaders().setBasicAuthentication(MY_APP_ID, MY_APP_SECRET);
                    }
                });

        HttpRequest request = requestFactory.buildPostRequest(url, hc);
        HttpResponse response = request.execute();

        JSONObject jo = null;
        try {
            if (response.isSuccessStatusCode()) {

                String json = response.parseAsString();
                Log.i("Success with " + json);

                JSONTokener tokener = null;
                tokener = new JSONTokener( json );
                jo = new JSONObject(tokener);

                // Sample response:
                // { "access_token": Your access token,
                //    "token_type": "bearer",
                //    "expires_in": Unix Epoch Seconds,
                //    "scope": A scope string, }                
            } else
                Log.w("Request failed with " + response.getStatusCode());
        } finally {
            response.disconnect();
        }

        return jo;
    }


    // http://www.reddit.com/dev/api
    // https://oauth.reddit.com/api/v1/me
    public static final String ENDPOINT_ID = OAUTH_API_DOMAIN + "/api/v1/me";
    public static final String ENDPOINT_SUBS = OAUTH_API_DOMAIN + "/subreddits/mine/";  // a list endpoint
        // Followed by 'subscriber', 'contributor', or 'moderator'


    public static JSONObject getInfo( final String token ) throws IOException {
        Log.v( "getInfo with token=" + token );

        GenericUrl url = new GenericUrl( ENDPOINT_ID );

        HttpRequestFactory requestFactory = HTTP_TRANSPORT
                .createRequestFactory(new HttpRequestInitializer() {
                    @Override
                    public void initialize(HttpRequest request) {
                        request.getHeaders().setAuthorization( "bearer " + token );                     
                    }
                });

        HttpRequest request = requestFactory.buildGetRequest( url );
        HttpResponse response = request.execute();

        JSONObject jo = null;

        try {
            if (response.isSuccessStatusCode()) {

                String json = response.parseAsString();

                //Log.i("Success with " + json);
                // Sample response:
                // {"name": "myName", "created": 1346020929.0, "created_utc": 1346017329.0, "link_karma": 1308, 
                // "comment_karma": 32602, "over_18": true, "is_gold": true, "is_mod": false, "has_verified_email": true, "id": "76gyp"}

                // Parse with org.json
                JSONTokener tokener = null;
                tokener = new JSONTokener( json );
                jo = new JSONObject(tokener);

            } else
                Log.w("Request failed with " + response.getStatusCode());
        } finally {
            response.disconnect();
        }

        return jo;
    }

    // A generic get fn to build the rest of my API calls around
    public static JSONObject get( final String surl, final String token ) throws IOException {
        Log.v( "get for URL=" + surl );

        GenericUrl url = new GenericUrl( surl );

        HttpRequestFactory requestFactory = HTTP_TRANSPORT
                .createRequestFactory(new HttpRequestInitializer() {
                    @Override
                    public void initialize(HttpRequest request) {
                        // request.setParser( new JsonObjectParser(JSON_FACTORY) );
                        request.getHeaders().setAuthorization( "bearer " + token );                     
                    }
                });

        HttpRequest request = requestFactory.buildGetRequest( url );
        HttpResponse response = request.execute();

        JSONObject jo = null;

        // Note the recommended use of finally { disconnect() }
        try {
            if (response.isSuccessStatusCode()) {

                String json = response.parseAsString();
                Log.i("Success with " + json);

                // Parse with org.json
                JSONTokener tokener = null;
                tokener = new JSONTokener( json );
                jo = new JSONObject(tokener);

                // Or Parse directly into Java objects using Jackson

            } else
                Log.w("Request failed with " + response.getStatusCode());
        } finally {
            response.disconnect();
        }

        return jo;
    }
}

This code was tested on GAE/J SDK 1.9.0. It is suitable for use on most platforms, including Android, but note that this form of OAuth is the server form - you will need to adjust for client side applications.