Jackson Date

1. Overview

In this tutorial, we’ll serialize dates with Jackson. We’ll start by serializing a simple java.util.Date, then Joda-Time as well as the Java 8 DateTime.

2. Serialize Date to Timestamp

First – let’s see how to serialize a simple java.util.Date with Jackson.

In the following example – we will serialize an instance of “Event” which has a Date field “eventDate“:

@Test
public void whenSerializingDateWithJackson_thenSerializedToTimestamp()
  throws JsonProcessingException, ParseException {

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm");
    df.setTimeZone(TimeZone.getTimeZone("UTC"));

    Date date = df.parse("01-01-1970 01:00");
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    mapper.writeValueAsString(event);
}

What’s important here is that Jackson will serialize the Date to a timestamp format by default (number of milliseconds since January 1st, 1970, UTC).

The actual output of the “event” serialization is:

{
   "name":"party",
   "eventDate":3600000
}

3. Serialize Date to ISO-8601

Serializing to this terse timestamp format is not optimal. Let’s now serialize the Date to the ISO-8601 format:

@Test
public void whenSerializingDateToISO8601_thenSerializedToText()
  throws JsonProcessingException, ParseException {

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm");
    df.setTimeZone(TimeZone.getTimeZone("UTC"));

    String toParse = "01-01-1970 02:30";
    Date date = df.parse(toParse);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    // StdDateFormat is ISO8601 since jackson 2.9
    mapper.setDateFormat(new StdDateFormat().withColonInTimeZone(true));
    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString("1970-01-01T02:30:00.000+00:00"));
}

Note how the representation of the date is now much more readable.

4. Configure ObjectMapper DateFormat

The previous solutions still lack the full flexibility of choosing the exact format to represent the java.util.Date instances.

Let’s now take a look at a configuration that will allow us to set our formats for representing dates:

@Test
public void whenSettingObjectMapperDateFormat_thenCorrect()
  throws JsonProcessingException, ParseException {

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm");

    String toParse = "20-12-2014 02:30";
    Date date = df.parse(toParse);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    mapper.setDateFormat(df);

    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString(toParse));
}

Note that, even though we’re now more flexible regarding the date format – we’re still using a global configuration at the level of the entire ObjectMapper.

5. Use @JsonFormat to Format Date

Next, let’s take a look at the @JsonFormat annotation to control the date format on individual classes instead of globally, for the entire application:

public class Event {
    public String name;

    @JsonFormat
      (shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
    public Date eventDate;
}

Now – let’s test it:

@Test
public void whenUsingJsonFormatAnnotationToFormatDate_thenCorrect()
  throws JsonProcessingException, ParseException {

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
    df.setTimeZone(TimeZone.getTimeZone("UTC"));

    String toParse = "20-12-2014 02:30:00";
    Date date = df.parse(toParse);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString(toParse));
}

6. Custom Date Serializer

Next – to get full control over the output, we’ll leverage a custom serializer for Dates:

public class CustomDateSerializer extends StdSerializer<Date> {

    private SimpleDateFormat formatter
      = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");

    public CustomDateSerializer() {
        this(null);
    }

    public CustomDateSerializer(Class t) {
        super(t);
    }

    @Override
    public void serialize (Date value, JsonGenerator gen, SerializerProvider arg2)
      throws IOException, JsonProcessingException {
        gen.writeString(formatter.format(value));
    }
}

Next – let’s use it as the serializer of our “eventDate” field:

public class Event {
    public String name;

    @JsonSerialize(using = CustomDateSerializer.class)
    public Date eventDate;
}

Finally – let’s test it:

@Test
public void whenUsingCustomDateSerializer_thenCorrect()
  throws JsonProcessingException, ParseException {

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");

    String toParse = "20-12-2014 02:30:00";
    Date date = df.parse(toParse);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString(toParse));
}

Further reading:

How To Serialize and Deserialize Enums with Jackson

How to serialize and deserialize an Enum as a JSON Object using Jackson 2.

Read more →

Jackson – Custom Serializer

Control your JSON output with Jackson 2 by using a Custom Serializer.

Read more →

Getting Started with Custom Deserialization in Jackson

Use Jackson to map custom JSON to any java entity graph with full control over the deserialization process.

Read more →

7. Serialize Joda-Time with Jackson

Dates aren’t always an instance of java.util.Date; actually – they’re more and more represented by some other class – and a common one is, of course, the DateTime implementation from the Joda-Time library.

Let’s see how we can serialize DateTime with Jackson.

We’ll make use of the jackson-datatype-joda module for out of the box Joda-Time support:

<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-joda</artifactId>
  <version>2.9.7</version>
</dependency>

And now we can simply register the JodaModule and be done:

@Test
public void whenSerializingJodaTime_thenCorrect()
  throws JsonProcessingException {
    DateTime date = new DateTime(2014, 12, 20, 2, 30,
      DateTimeZone.forID("Europe/London"));

    ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(new JodaModule());
    mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

    String result = mapper.writeValueAsString(date);
    assertThat(result, containsString("2014-12-20T02:30:00.000Z"));
}

8. Serialize Joda DateTime with Custom Serializer

If we don’t want the extra Joda-Time Jackson dependency – we can also make use of a custom serializer (similar to the earlier examples) to get DateTime instances serialized cleanly:

public class CustomDateTimeSerializer extends StdSerializer<DateTime> {

    private static DateTimeFormatter formatter =
      DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");

    public CustomDateTimeSerializer() {
        this(null);
    }

     public CustomDateTimeSerializer(Class<DateTime> t) {
         super(t);
     }

    @Override
    public void serialize
      (DateTime value, JsonGenerator gen, SerializerProvider arg2)
      throws IOException, JsonProcessingException {
        gen.writeString(formatter.print(value));
    }
}

Next – let’s use it as our property “eventDate” serializer:

public class Event {
    public String name;

    @JsonSerialize(using = CustomDateTimeSerializer.class)
    public DateTime eventDate;
}

Finally – let’s put everything together and test it:

@Test
public void whenSerializingJodaTimeWithJackson_thenCorrect()
  throws JsonProcessingException {

    DateTime date = new DateTime(2014, 12, 20, 2, 30);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString("2014-12-20 02:30"));
}

9. Serialize Java 8 Date with Jackson

Next – let’s see how to serialize Java 8 DateTime – in this example, LocalDateTime – using Jackson. We can make use of the jackson-datatype-jsr310 module:

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
    <version>2.9.7</version>
</dependency>

Now, all we need to do is register the JavaTimeModule (JSR310Module is deprecated) and Jackson will take care of the rest:

@Test
public void whenSerializingJava8Date_thenCorrect()
  throws JsonProcessingException {
    LocalDateTime date = LocalDateTime.of(2014, 12, 20, 2, 30);

    ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(new JavaTimeModule());
    mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

    String result = mapper.writeValueAsString(date);
    assertThat(result, containsString("2014-12-20T02:30"));
}

10. Serialize Java 8 Date Without Any Extra Dependency

If you don’t want the extra dependency, you can always use a custom serializer to write out the Java 8 DateTime to JSON:

public class CustomLocalDateTimeSerializer
  extends StdSerializer<LocalDateTime> {

    private static DateTimeFormatter formatter =
      DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");

    public CustomLocalDateTimeSerializer() {
        this(null);
    }

    public CustomLocalDateTimeSerializer(Class<LocalDateTime> t) {
        super(t);
    }

    @Override
    public void serialize(
      LocalDateTime value,
      JsonGenerator gen,
      SerializerProvider arg2)
      throws IOException, JsonProcessingException {

        gen.writeString(formatter.format(value));
    }
}

Next – let’s use the serializer for our “eventDate” field:

public class Event {
    public String name;

    @JsonSerialize(using = CustomLocalDateTimeSerializer.class)
    public LocalDateTime eventDate;
}

Now – let’s test it:

@Test
public void whenSerializingJava8DateWithCustomSerializer_thenCorrect()
  throws JsonProcessingException {

    LocalDateTime date = LocalDateTime.of(2014, 12, 20, 2, 30);
    Event event = new Event("party", date);

    ObjectMapper mapper = new ObjectMapper();
    String result = mapper.writeValueAsString(event);
    assertThat(result, containsString("2014-12-20 02:30"));
}

11. Deserialize Date

Next – let’s see how to deserialize a Date with Jackson. In the following example – we deserialize an “Event” instance containing a date:

@Test
public void whenDeserializingDateWithJackson_thenCorrect()
  throws JsonProcessingException, IOException {

    String json = "{"name":"party","eventDate":"20-12-2014 02:30:00"}";

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
    ObjectMapper mapper = new ObjectMapper();
    mapper.setDateFormat(df);

    Event event = mapper.readerFor(Event.class).readValue(json);
    assertEquals("20-12-2014 02:30:00", df.format(event.eventDate));
}

12. Deserialize Joda ZonedDateTime with Time Zone Preserved

In its default configuration, Jackson adjusts the time zone of a Joda ZonedDateTime to the time zone of the local context. As, by default, the time zone of the local context is not set and has to be configured manually, Jackson adjusts the time zone to GMT:

@Test
public void whenDeserialisingZonedDateTimeWithDefaults_thenNotCorrect()
  throws IOException {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.findAndRegisterModules();
    objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
    ZonedDateTime now = ZonedDateTime.now(ZoneId.of("Europe/Berlin"));
    String converted = objectMapper.writeValueAsString(now);

    ZonedDateTime restored = objectMapper.readValue(converted, ZonedDateTime.class);
    System.out.println("serialized: " + now);
    System.out.println("restored: " + restored);
    assertThat(now, is(restored));
}

This test case will fail with output:

serialized: 2017-08-14T13:52:22.071+02:00[Europe/Berlin]
restored: 2017-08-14T11:52:22.071Z[UTC]

Fortunately, there is a quick and simple fix for this odd default-behavior: we just have to tell Jackson, not to adjust the time zone.

This can be done by adding the below line of code to the above test case:

objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);

Note that, to preserve time zone we also have to disable the default behavior of serializing the date to the timestamp.

13. Custom Date Deserializer

Let’s also see how to use a custom Date deserializer; we’ll write a custom deserializer for the property “eventDate“:

public class CustomDateDeserializer extends StdDeserializer<Date> {

    private SimpleDateFormat formatter =
      new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");

    public CustomDateDeserializer() {
        this(null);
    }

    public CustomDateDeserializer(Class<?> vc) {
        super(vc);
    }

    @Override
    public Date deserialize(JsonParser jsonparser, DeserializationContext context)
      throws IOException, JsonProcessingException {
        String date = jsonparser.getText();
        try {
            return formatter.parse(date);
        } catch (ParseException e) {
            throw new RuntimeException(e);
        }
    }
}

Next – let’s use it as the “eventDate” deserializer:

public class Event {
    public String name;

    @JsonDeserialize(using = CustomDateDeserializer.class)
    public Date eventDate;
}

And finally – let’s test it:

@Test
public void whenDeserializingDateUsingCustomDeserializer_thenCorrect()
  throws JsonProcessingException, IOException {

    String json = "{"name":"party","eventDate":"20-12-2014 02:30:00"}";

    SimpleDateFormat df = new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
    ObjectMapper mapper = new ObjectMapper();

    Event event = mapper.readerFor(Event.class).readValue(json);
    assertEquals("20-12-2014 02:30:00", df.format(event.eventDate));
}

14. Conclusion

In this extensive Date article, we looked at most relevant ways Jackson can help marshalli and unmarshall a date to JSON using a sensible format we have control over.

The implementation of all these examples and code snippets can be found in my GitHub project – this is a Maven-based project, so it should be easy to import and run as it is.

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