Gson can't parse my json date in java

Question

I'm trying to make some test for a java-ee application that uses rest, but when I tried to format some json with gson I got the following error:

java.text.ParseException: Failed to parse date ["1489752692000']: Invalid time zone indicator '9'

This happened when I initialized my Gson with Gson gson = new Gson();, I found this question on StackOverflow where the solution was to make a custom DateDeseriliazer class and intialize like this:

Gson gson = new GsonBuilder().registerTypeAdapter(Date.class, new GsonDateFormatter()).create();

Here is my version of the DateDeserializer class:

public class GsonDateFormatter implements JsonDeserializer<Date> {

    private final DateFormat dateFormat;

    public GsonDateFormatter() {
        dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
        dateFormat.setTimeZone(TimeZone.getTimeZone("CET"));
    }

    public synchronized Date deserialize(JsonElement jsonElement,Type type,JsonDeserializationContext jsonDeserializationContext) {
        try {
            return dateFormat.parse(jsonElement.getAsString());
        } catch (ParseException e) {
            throw new JsonParseException(e);
        }
    }
}

But this only changes the error message to:

java.text.ParseException: Unparseable date: "1489752692000"

So I'm not quite sure how to solve this now and I hope someone can help me with this.

Thanks in advance.

`1489752692000` obviously is not of the format `yyyy-MM-dd'T'HH:mm:ss'Z'`, so why did you give that format? — OneCricketeer, Mar 20 '17 at 16:27
@cricket_007 because I wasn't sure what format to put there and the other post used that format — Dennis van Opstal, Mar 20 '17 at 16:28
Read the other post again. Look at their dates in the JSON strings. — OneCricketeer, Mar 20 '17 at 16:29
@cricket_007 I saw that, but like I said, I didn't know what format mine was and I wasn't sure if that was the input format or something else — Dennis van Opstal, Mar 20 '17 at 16:30
You have what is called "milliseconds since epoch", and you don't need `SimpleDateFormat` for that unless you wanted to convert the number into a human-readable format as per the table in [`SimpleDateFormat` documentation](http://docs.oracle.com/javase/8/docs/api/java/text/SimpleDateFormat.html) — OneCricketeer, Mar 20 '17 at 16:35
@DennisvanOpstal You don't need `SimpleDateFormat` here: you're trying to parse _number of ms since January 1, 1970_ using the given pattern. The pattern you're trying to use is used to parse strings like `1970-01-01T00:00:00Z`. Just replace `dateFormat.parse` with `return new Date(jsonElement.getAsLong())`. — Lyubomyr Shaydariv, Mar 20 '17 at 16:36
@LyubomyrShaydariv that works, if you create an answer out of that comment, I'll accept it as answer — Dennis van Opstal, Mar 20 '17 at 16:38
@cricket_007 Oh, okay, I think I was a bit too focussed on the example to see that as a possibility — Dennis van Opstal, Mar 20 '17 at 16:39

score 2 · Accepted Answer · edited May 23 '17 at 12:32

2

You have what appears to be milliseconds since epoch.

It's recommended to use java.time API now in Java 8 instead of SimpleDateFormat

import java.time.Instant;
import java.time.ZonedDateTime;
import java.timeZoneOffset;

// ... 

long epoch = Long.parseLong(jsonElement.getAsString()); // Or if you can do jsonElement.getAsLong()
Instant instant = Instant.ofEpochMilli(epoch);
ZonedDateTime zdt = ZonedDateTime.ofInstant(instant, ZoneOffset.UTC); // 2017-03-17T12:11:32Z

But, in any case, you don't need SimpleDateFormat to return a Date from a long value.

public synchronized Date deserialize(JsonElement jsonElement,Type type,JsonDeserializationContext jsonDeserializationContext) {
    long epoch = jsonElement.getAsLong();
    return new Date(epoch);
 }

edited May 23 '17 at 12:32

Community

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answered Mar 20 '17 at 16:43

OneCricketeer

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This just gives me red lines everywhere saying `Usage of API documented as @since 1.6+` and isn't `jsonElement.getAsLong();` sufficient? – Dennis van Opstal Mar 20 '17 at 16:49
It is sufficient, yes. The import statements go at the top of the file, so not sure what else you are doing wrong unless you are not compiling with Java 8 – OneCricketeer Mar 20 '17 at 16:52
The imports are where they belong on the top of the file (also with those red lines) – Dennis van Opstal Mar 20 '17 at 16:54
Like I said, if you can't import, then you aren't compiling against Java 8 – OneCricketeer Mar 20 '17 at 16:55

Gson can't parse my json date in java

1 Answers1