public class Installation {
    private static String sID = null;
    private static final String INSTALLATION = "INSTALLATION";

    public synchronized static String id(Context context) {
        if (sID == null) {
            File installation = new File(context.getFilesDir(), INSTALLATION);
            try {
                if (!installation.exists())
                writeInstallationFile(installation);
                sID = readInstallationFile(installation);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
        }
        return sID;
    }

    private static String readInstallationFile(File installation) throws IOException {
        RandomAccessFile f = new RandomAccessFile(installation, "r");
        byte[] bytes = new byte[(int) f.length()];
        f.readFully(bytes);
        f.close();
        return new String(bytes);
    }

    private static void writeInstallationFile(File installation) throws IOException {
        FileOutputStream out = new FileOutputStream(installation);
        String id = UUID.randomUUID().toString();
        out.write(id.getBytes());
        out.close();
    }
}

import android.content.Context;
import android.content.SharedPreferences;
import android.provider.Settings.Secure;
import android.telephony.TelephonyManager;

import java.io.UnsupportedEncodingException;
import java.util.UUID;

public class DeviceUuidFactory {
    protected static final String PREFS_FILE = "device_id.xml";
    protected static final String PREFS_DEVICE_ID = "device_id";

    protected static UUID uuid;

    /**
    * Returns a unique UUID for the current android device. As with all UUIDs, this unique ID is "very highly likely"
    * to be unique across all Android devices. Much more so than ANDROID_ID is.
    *
    * The UUID is generated by using ANDROID_ID as the base key if appropriate, falling back on
    * TelephonyManager.getDeviceID() if ANDROID_ID is known to be incorrect, and finally falling back
    * on a random UUID that's persisted to SharedPreferences if getDeviceID() does not return a
    * usable value.
    *
    * In some rare circumstances, this ID may change. In particular, if the device is factory reset a new device ID
    * may be generated. In addition, if a user upgrades their phone from certain buggy implementations of Android 2.2
    * to a newer, non-buggy version of Android, the device ID may change. Or, if a user uninstalls your app on
    * a device that has neither a proper Android ID nor a Device ID, this ID may change on reinstallation.
    *
    * Note that if the code falls back on using TelephonyManager.getDeviceId(), the resulting ID will NOT
    * change after a factory reset. Something to be aware of.
    *
    * Works around a bug in Android 2.2 for many devices when using ANDROID_ID directly.
    *
    * @see http://code.google.com/p/android/issues/detail?id=10603
    *
    * @return a UUID that may be used to uniquely identify your device for most purposes.
    */
    public DeviceUuidFactory(Context context) {
        if( uuid ==null ) {
            synchronized (DeviceUuidFactory.class) {
                if( uuid == null) {
                    final SharedPreferences prefs = context.getSharedPreferences(PREFS_FILE, 0);
                    final String id = prefs.getString(PREFS_DEVICE_ID, null );

                    if (id != null) {
                        // Use the ids previously computed and stored in the prefs file
                        uuid = id;
                    } else {
                        final String androidId = Secure.getString(context.getContentResolver(), Secure.ANDROID_ID);

                        // Use the Android ID unless it's broken, in which case fallback on deviceId,
                        // unless it's not available, then fallback on a random number which we store
                        // to a prefs file
                        try {
                            if (!"9774d56d682e549c".equals(androidId)) {
                                uuid = UUID.nameUUIDFromBytes(androidId.getBytes("utf8"));
                            } else {
                                final String deviceId = ((TelephonyManager) context.getSystemService( Context.TELEPHONY_SERVICE )).getDeviceId();
                                uuid = deviceId != null ? UUID.nameUUIDFromBytes(deviceId.getBytes("utf8")) : UUID.randomUUID();
                            }
                        } catch (UnsupportedEncodingException e) {
                            throw new RuntimeException(e);
                        }

                        // Write the value out to the prefs file
                        prefs.edit().putString(PREFS_DEVICE_ID, uuid.toString()).commit();

                    }
                }
            }
        }
    }
}