Saving and retrieving date in Firebase

Question

I have a model with the following structure

public class OfferModel {     private String mImageUrl;     private String mOfferCode;     private String mOfferTitle;     private String mOfferDescription;     private boolean mIsRunning;     private String mCreatorUid;     private Date mStartDate; } 

Everything else works fine on saving. It saves in Firebase Realtime database as

startDate     date: 22     day: 3     hours: 23     minutes: 20     month: 5     seconds: 50     time: 1466617850476     timezoneOffset: -330     year: 116 

But when I try to retrieve it, the date gives the following error -

java.lang.ClassCastException: java.util.HashMap cannot be cast to java.util.Date at com.localvine.models.OfferModel.<init>(OfferModel.java:37) at com.localvine.managers.OfferManager$1.onDataChange(OfferManager.java:62) at com.google.android.gms.internal.zzafp.zza(Unknown Source) at com.google.android.gms.internal.zzagp.zzSu(Unknown Source) at com.google.android.gms.internal.zzags$1.run(Unknown Source) at android.os.Handler.handleCallback(Handler.java:615) 

I understand that Firebase doesn't support Java Date object, but since it's saving them in a map, how can I get back the date from that map? Is there any proper way of saving and retrieving dates in Firebase Android?

Answer 1

You can store the date as an epoch date. It's a long that you can get using your system time System.currentTimeMillis(); or by using the Firebase server time with their ServerValue.TIMESTAMP. The thing with the first option is that it changes with timezones and system settings. So if you store the date as a long, you just have to change your OfferModel field mStartDate to a long and then use new Date(long) to get the corresponding Date when retrieving the object.

Answer 2

Use ISO 8601 date format:

SimpleDateFormat ISO_8601_FORMAT = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:sss'Z'");  String now = ISO_8601_FORMAT.format(new Date()); 

Representing Date as a String has two greater advantages:

• It is human readable ("2018-03-30T13:18:39.516Z" vs 1522415925281)
• At the browser side, you can simply invokes new Date("2018-03-30T13:18:39.516Z")

This is quite useful if you have Android and browsers both consuming Firebase data.