Serialize Java8 LocalDateTime to UTC Timestamp using Jackson

Question

I've just converted over many of my Dates to LocalDateTime per the new(ish) java 8 time package. I've enjoyed the switch so far until I started trying to serialize and deserialize.

How can I configure Jackson to support them?:

LocalDateTime --serialize--> UTC Timestamp --deserialize--> LocalDateTime?

There's plenty of material on here about converting to formatted strings, but I can't seem to find an out-of-the-box solution to utc timestamps.

Answer 1

You can custom a serializer and a deserializer for LocalDateTime, for exmaple:

CustomLocalDateTimeSerializer

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

import java.io.IOException;
import java.time.LocalDateTime;
import java.time.ZoneId;

public class CustomLocalDateTimeSerializer extends StdSerializer<LocalDateTime> {

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

    protected CustomLocalDateTimeSerializer() {
        this(null);
    }

    @Override
    public void serialize(LocalDateTime value, JsonGenerator gen, SerializerProvider sp)
            throws IOException {
        Long epoch = value.atZone(ZoneId.systemDefault()).toInstant().getEpochSecond();
        gen.writeString(epoch.toString());
    }
}

CustomLocalDateTimeDesSerializer：

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;

import java.io.IOException;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;

class CustomLocalDateTimeDesSerializer extends StdDeserializer<LocalDateTime> {

    protected CustomLocalDateTimeDesSerializer() {
        this(null);
    }

    protected CustomLocalDateTimeDesSerializer(Class<LocalDateTime> t) {
        super(t);
    }

    @Override
    public LocalDateTime deserialize(JsonParser jsonparser, DeserializationContext context)
            throws IOException {
        Long timestamp = Long.parseLong(jsonparser.getText());
        return LocalDateTime.ofInstant(Instant.ofEpochSecond(timestamp), ZoneId.systemDefault());
    }
}

And use the them:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;

import java.time.LocalDateTime;

public class RestObject {

    private LocalDateTime timestamp = LocalDateTime.now();

    @JsonSerialize(using = CustomLocalDateTimeSerializer.class)
    @JsonDeserialize(using = CustomLocalDateTimeDesSerializer.class)
    public LocalDateTime getTimestamp() {
        return timestamp;
    }

    public static void main(String[] args) throws Exception {
        ObjectMapper objectMapper = new ObjectMapper();
        // {"timestamp":"1549026058"}
        System.out.println(objectMapper.writeValueAsString(new RestObject()));
    }
}

Answer 2

The following solution solves the task of serialize/deserialise the LocalDateTime to the timestamp and relevant at least for spring-boot v1.5 and also includes next points that are not taken into account in the @xingbin's answer:

• If there is a necessity to have the same behaviour as for java.util.Date have to use the toInstant().toEpochMilli() instead the toInstant().getEpochSecond()
• Check on null the value to deserialize
• And optional point: specify this serialization/deserialization configuration for the Jackson ObjectMapper

The timestamp serializer class:

public class LocalDateTimeSerializer extends StdSerializer<LocalDateTime> {
    private static final ZoneId DEFAULT_ZONE_ID = ZoneId.of("UTC");

    public LocalDateTimeSerializer() {
        super(LocalDateTime.class);

    }

    @Override
    public void serialize(final LocalDateTime value,
                          final JsonGenerator generator,
                          final SerializerProvider provider) throws IOException {
        if (value != null) {
            final long mills = value.atZone(DEFAULT_ZONE_ID).toInstant().toEpochMilli();
            generator.writeNumber(mills);
        } else {
            generator.writeNull();
        }
    }
}

The timestamp deserializer class:

public class LocalDateTimeDeserializer extends StdDeserializer<LocalDateTime> {
    private static final ZoneId DEFAULT_ZONE_ID = ZoneId.of("UTC");

    public LocalDateTimeDeserializer() {
        super(LocalDateTime.class);
    }

    @Override
    public LocalDateTime deserialize(final JsonParser parser,
                                     final DeserializationContext context) throws IOException {
        final long value = parser.getValueAsLong();
        return LocalDateTime.ofInstant(Instant.ofEpochMilli(value), DEFAULT_ZONE_ID);
    }
}

The object mapper configuration:

@Configuration
public class ObjectMapperConfiguration {
    @Bean
    public ObjectMapper objectMapper() {
        final ObjectMapper objectMapper = new ObjectMapper();
        final SimpleModule module = new SimpleModule();
        module.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer());
        module.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer());
        objectMapper.registerModule(module);
        return objectMapper;
    }
}