Java – Default timezone for DateTime deserialization with Jackson (Joda-Time module)

datetimedeserializationjacksonjavajodatime

This question is about deserialization to Joda-Time DateTime using jackson-datatype-joda module for Jackson. Is there a default timezone that date strings will be deserialized into? If so, what is it? Is it UTC?

I need to ask this because the Jackson documentation is not specific for Joda-Time DateTime. I found in this article (http://wiki.fasterxml.com/JacksonFAQDateHandling) that Jackson will assume GMT as the default time zone for deserializing into java.util.Date or java.util.Calendar. However, there is no mention of Joda-Time data types in this document. In addition, I specifically need strings to deserialize into DateTime objects using the UTC timezone, not GMT: although these two zones are very similar, there are some small differences and therefore GMT will not be feasible for me.

Thank you.

Best Answer

The source code for DateTimeDeserializer shows it uses the timezone from DeserializationContext which is provided by ObjectMapper during deserialization. If you look at ObjectMapper API, you will see there is method for setting the timezone:

public ObjectMapper setTimeZone(TimeZone tz)

Thus you can use this method to configure your ObjectMapper and set the timezone to the correct one.

For what concerns the default value, it seems the Javadoc says one thing, but the code shows another.

Javadoc for ObjectMapper.setTimeZone(TimeZone tz):

/**
  * Method for overriding default TimeZone to use for formatting.
  * Default value used is {@link TimeZone#getDefault()}.
  */

However, the code sets the timezone explicitly on:

protected final static BaseSettings DEFAULT_BASE = new BaseSettings(
    ...
    // TimeZone.getDefault()
    TimeZone.getTimeZone("GMT"),
    ...

So, apparently, it actually uses GMT, and not the default JVM default.

I would say that probably the best choice would be not relying on this and set it by yourself on ObjectMapper.setTimeZone(TimeZone tz).

Related Solutions

Python – How to convert local time string to UTC

First, parse the string into a naive datetime object. This is an instance of datetime.datetime with no attached timezone information. See its documentation.

Use the pytz module, which comes with a full list of time zones + UTC. Figure out what the local timezone is, construct a timezone object from it, and manipulate and attach it to the naive datetime.

Finally, use datetime.astimezone() method to convert the datetime to UTC.

Source code, using local timezone "America/Los_Angeles", for the string "2001-2-3 10:11:12":

from datetime import datetime   
import pytz

local = pytz.timezone("America/Los_Angeles")
naive = datetime.strptime("2001-2-3 10:11:12", "%Y-%m-%d %H:%M:%S")
local_dt = local.localize(naive, is_dst=None)
utc_dt = local_dt.astimezone(pytz.utc)

From there, you can use the strftime() method to format the UTC datetime as needed:

utc_dt.strftime("%Y-%m-%d %H:%M:%S")

Mysql – How to set a default value for a MySQL Datetime column

IMPORTANT EDIT: It is now possible to achieve this with DATETIME fields since MySQL 5.6.5, take a look at the other post below...

Previous versions can't do that with DATETIME...

But you can do it with TIMESTAMP:

mysql> create table test (str varchar(32), ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);
Query OK, 0 rows affected (0.00 sec)

mysql> desc test;
+-------+-------------+------+-----+-------------------+-------+
| Field | Type        | Null | Key | Default           | Extra |
+-------+-------------+------+-----+-------------------+-------+
| str   | varchar(32) | YES  |     | NULL              |       | 
| ts    | timestamp   | NO   |     | CURRENT_TIMESTAMP |       | 
+-------+-------------+------+-----+-------------------+-------+
2 rows in set (0.00 sec)

mysql> insert into test (str) values ("demo");
Query OK, 1 row affected (0.00 sec)

mysql> select * from test;
+------+---------------------+
| str  | ts                  |
+------+---------------------+
| demo | 2008-10-03 22:59:52 | 
+------+---------------------+
1 row in set (0.00 sec)

mysql>

CAVEAT: IF you define a column with CURRENT_TIMESTAMP ON as default, you will need to ALWAYS specify a value for this column or the value will automatically reset itself to "now()" on update. This means that if you do not want the value to change, your UPDATE statement must contain "[your column name] = [your column name]" (or some other value) or the value will become "now()". Weird, but true. I am using 5.5.56-MariaDB

Best Answer

Related Solutions

Python – How to convert local time string to UTC

Mysql – How to set a default value for a MySQL Datetime column

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