Android Google Authentication integration

Authenticator.java

import android.accounts.Account;
import android.accounts.AccountManager;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.Dialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;

class Authenticator {
	public final static int REQUEST_AUTHENTICATE = 1235;
	public final static int DIALOG_ACCOUNTS = 235664;

	private final static String ACCOUNT_TYPE = "com.google";
	private final static String AUTH_TOKEN_TYPE = "mail";

	public static interface TokenHandler {
		void onSuccessfullAuthentication(String token);
	}

	private final Activity activity;
	private final Authenticator.TokenHandler handler;

	public Authenticator(Activity activity, Authenticator.TokenHandler handler) {
		this.activity = activity;
		this.handler = handler;
	}

	public void authenticate() {
		String accountName = new ApplicationStorage(activity).getUsername();
		Account[] accounts = getAccounts();
		if (accountName != null) {
			for (int i = 0; i < accounts.length; i++) {
				Account account = accounts[i];
				if (accountName.equals(account.name)) {
					continueWithAccount(account);
					return;
				}
			}
		}
		if (accounts.length == 0) {
			new Thread() {
				@Override
				public void run() {
					try {
						final Bundle bundle = getAccountManager().addAccount(ACCOUNT_TYPE, AUTH_TOKEN_TYPE, null, null, activity, null, null)
								.getResult();
						activity.runOnUiThread(new Runnable() {
							public void run() {
								String accountName = (String) bundle.get(AccountManager.KEY_ACCOUNT_NAME);
								System.out.println("Created account : + accountName");
								authenticate();
							}
						});
					} catch (Exception e) {
						handleException(e);
					}
				};
			}.start();
		} else if (accounts.length == 1) {
			continueWithAccount(accounts[0]);
		} else {
			activity.showDialog(DIALOG_ACCOUNTS);
		}
	}

	private Account[] getAccounts() {
		return getAccountManager().getAccountsByType(ACCOUNT_TYPE);
	}

	private AccountManager getAccountManager() {
		return AccountManager.get(activity);
	}

	private void continueWithAccount(final Account account) {
		new ApplicationStorage(activity).setUsername(account.name);
		new Thread() {
			@Override
			public void run() {
				try {
					final Bundle bundle = getAccountManager().getAuthToken(account, AUTH_TOKEN_TYPE, true, null, null).getResult();
					activity.runOnUiThread(new Runnable() {
						public void run() {
							try {
								if (bundle.containsKey(AccountManager.KEY_AUTHTOKEN)) {
									handler.onSuccessfullAuthentication(bundle.getString(AccountManager.KEY_AUTHTOKEN));
								} else if (bundle.containsKey(AccountManager.KEY_INTENT)) {
									Intent intent = bundle.getParcelable(AccountManager.KEY_INTENT);
									intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
									activity.startActivityForResult(intent, REQUEST_AUTHENTICATE);
								}
							} catch (Exception e) {
								handleException(e);
							}
						}
					});
				} catch (Exception e) {
					handleException(e);
				}
			}
		}.start();
	}

	private void handleException(Exception e) {
		Log.v("Karma collector", "Authentication failure", e);
		throw new RuntimeException(e);
	}

	public Dialog createDialog(int id) {
		switch (id) {
		case Authenticator.DIALOG_ACCOUNTS:
			AlertDialog.Builder builder = new AlertDialog.Builder(activity);
			builder.setTitle("Select a Google account");
			final Account[] accounts = getAccounts();
			String[] names = new String[accounts.length];
			for (int i = 0; i < accounts.length; i++) {
				names[i] = accounts[i].name;
			}
			builder.setItems(names, new DialogInterface.OnClickListener() {
				public void onClick(DialogInterface dialog, int which) {
					continueWithAccount(accounts[which]);
				}
			});
			return builder.create();
		}
		return null;
	}

	public boolean onActivityResult(int requestCode, int resultCode, Intent data) {
		if (requestCode == REQUEST_AUTHENTICATE) {
			if (resultCode == Activity.RESULT_OK) {
				authenticate();
			} else {
				activity.showDialog(Authenticator.DIALOG_ACCOUNTS);
			}
			return true;
		}
		return false;
	}
}


class ApplicationStorage {
	private final static String PREF = "lollers";
	private final Context context;
	private String username;

	public ApplicationStorage(Context context) {
		this.context = context;
	}

	public String getUsername() {
		if (Strings.isNullOrEmpty(username)) {
			username = loadUsernameFromStorage();
		}
		return username;
	}

	public void setUsername(String name) {
		this.username = name;
		SharedPreferences settings = context.getSharedPreferences(PREF, 0);
		SharedPreferences.Editor editor = settings.edit();
		editor.putString("accountName", name);
		editor.commit();
	}

	private String loadUsernameFromStorage() {
		SharedPreferences settings = context.getSharedPreferences(PREF, 0);
		return settings.getString("accountName", null);
	}
}

In addition, you need some hooks in your Activity:

    @Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if (!authenticator.onActivityResult(requestCode, resultCode, data)) {
        // Your other result handling code goes here
    }
}


@Override
protected Dialog onCreateDialog(int id) {
    Dialog authDialog = authenticator.createDialog(id);
    if (authDialog == null) {
        // Your other dialogs are created here
    }
    return authDialog;
}