how to convert incoming Json date into java date format?

Question

I am working on Xero accounts Apis In json response i am getting date like below

 "Date": "/Date(1455447600000+1300)/",

also same date in getting in dateString field like

"DateString": "2016-02-15T00:00:00",

i am trying to convert above date into string but getting different date. as in our api both dates are same, in Date field and DateString field.

Long longDate=Long.valueOf("1455447600000")+Long.valueOf("1300");
        Date date = new Date(longDate);

        //TimeZone timeZone = TimeZone.getTimeZone("UTC"); //also tried this
        Calendar cal=Calendar.getInstance();
        cal.setTime(date);
        System.out.println(cal.getTime());

output: Sun Feb 14 16:30:01 IST 2016 14 Feb but in StringDate it's 15 Feb

json:

[
  {
    "Date": "/Date(1455447600000+1300)/",
    "Type": "ACCREC",
    "Total": 460,
    "Status": "AUTHORISED",
    "Contact": {
      "Name": "nn",
      "Phones": [

      ],
      "Addresses": [

      ],
      "ContactID": "6831fd62-d6f1-4dc7-9338-24566074ecf6",
      "ContactGroups": [

      ],
      "ContactPersons": [

      ],
      "HasValidationErrors": false
    },
    "DueDate": "/Date(1455620400000+1300)/",
    "Payments": [

    ],
    "SubTotal": 460,
    "TotalTax": 0,
    "AmountDue": 460,
    "HasErrors": false,
    "InvoiceID": "dcf1f09e-3e98-443e-981e-cdd9f296d607",
    "LineItems": [
      {
        "TaxType": "OUTPUT",
        "ItemCode": "Item2",
        "Quantity": 20,
        "Tracking": [

        ],
        "TaxAmount": 0,
        "LineAmount": 460,
        "LineItemID": "2a6c5078-a462-4e8c-b277-d1164885b7d9",
        "UnitAmount": 23,
        "AccountCode": "200",
        "Description": "Item2"
      }
    ],
    "Reference": "43223",
    "AmountPaid": 0,
    "DateString": "2016-02-15T00:00:00",
    "CreditNotes": [

    ],
    "Prepayments": [

    ],
    "CurrencyCode": "INR",
    "CurrencyRate": 1,
    "IsDiscounted": false,
    "Overpayments": [

    ],
    "DueDateString": "2016-02-17T00:00:00",
    "InvoiceNumber": "INV-0002",
    "AmountCredited": 0,
    "HasAttachments": false,
    "UpdatedDateUTC": "/Date(1455475695503+1300)/",
    "LineAmountTypes": "Exclusive"
  }
]

Answer 1

The +1300 is not a milliseconds offset, it's an hour + minute offset. If you parse just the date part as a long:

Long longDate=Long.valueOf("1455447600000");
Date date = new Date(longDate);
System.out.println(date);

You get (I'm in GMT timezone)

Sun Feb 14 11:00:00 GMT 2016

And you can see that 11 + 13 = 24, and 24 hours is the next day.

You can get the timezone from the offset, knowing the offset is 13 hours and zero minutes:

Calendar c=Calendar.getInstance(TimeZone.getTimeZone(TimeZone.getAvailableIDs(13*3600*1000)[0]));
c.setTimeInMillis(longDate);
DateFormat df=DateFormat.getDateInstance();
df.setTimeZone(c.getTimeZone());
System.out.println(df.format(c.getTime()));

Which gives me

Feb 15, 2016

Here so I calculate the offset as being 13 hours, hence 13*3600 seconds, hence 13*3600*1000 milliseconds. So you can parse your string: what's before the plus sign is the time, what's after is the timezone.