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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 with Jackson
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
Clearly serializing to this terse timestamp format is not optimal. Let’s now serialize the Date to the ISO-8601 format.
If we disable the use of timestamps, ISO-8601 will be automatically used instead as in the following example:
@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);
String result = mapper.writeValueAsString(event);
assertThat(result, containsString("1970-01-01T02:30:00.000+0000"));
}
Note how the representation of the date is now much more readable – though maybe not as clean as it could be.
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 own 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 in terms of 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 JsonSerializer<Date> {
private static SimpleDateFormat formatter =
new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
@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));
}
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>2.4.0</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 JsonSerializer<DateTime> {
private static DateTimeFormatter formatter =
DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");
@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>2.4.0</version>
</dependency>
Now, all we need to do is register the JSR310Module 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 JSR310Module());
mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
String result = mapper.writeValueAsString(date);
assertThat(result, containsString("2014-12-20T02:30"));
}
10. Serialize Java 8 Date with Jackson
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 JsonSerializer<LocalDateTime> {
private static DateTimeFormatter formatter =
DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
@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.reader(Event.class).readValue(json);
assertEquals("20-12-2014 02:30:00", df.format(event.eventDate));
}
12. 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 JsonDeserializer<Date> {
private static SimpleDateFormat formatter =
new SimpleDateFormat("dd-MM-yyyy hh:mm:ss");
@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.reader(Event.class).readValue(json);
assertEquals("20-12-2014 02:30:00", df.format(event.eventDate));
}
13. Conclusion
In this extensive Date article we looked at most relevant ways Jackson can help marshalling and unmarshall a date to JSON using a sensible format we have control over.
I usually post about Jackson and JSON stuff on Google+ - you can follow me there: