Convert date to string elastic search

I want to get year from date in elastic search.My mapping is like -

"timeModified": 
{
   "type": "date",
    "format": "strict_date_optional_time||epoch_millis"
}

And my data store in elastic search is -

"timeModified": "2015-03-12T13:18:50.000+05:30"

I want to get year from the date.When I execute the below query -

{
    "query" : {
        "match_all": {}
    },
    "script_fields" : {
        "left_field" : {
            "script" : {
                "inline": "doc.timeModified.value.substring(0, length)",
                "params": {
                    "length": 4
                }
            }
        }
    }
}

It give me exception -

"No signature of method: java.lang.Long.substring() is applicable for argument types: (java.lang.Integer, java.lang.Integer) values: [0, 4]\nPossible solutions: toString(), toString(), toString(), toString(long, int)"

If I have option to convert the field value date to string without change in my actual mapping type, I get the correct value. So please suggest how to convert in string in elastic search query. Or if any other option to get year from date then also suggest.

The error you're getting is because the field value is a Long not a String. However, you can also access the date value directly by doing it like this:

{
    "query" : {
        "match_all": {}
    },
    "script_fields" : {
        "left_field" : {
            "script" : {
                "inline": "doc.timeModified.date.getYear()"
            }
        }
    }
}