serialize/deserialize java 8 java.time with Jackson JSON mapper

Question

How do I use Jackson JSON mapper with Java 8 LocalDateTime?

org.codehaus.jackson.map.JsonMappingException: Can not instantiate value of type [simple t

Answer 1

Update: Leaving this answer for historical reasons, but I don't recommend it. Please see the accepted answer above.

Tell Jackson to map using your custom [de]serialization classes:

@JsonSerialize(using = LocalDateTimeSerializer.class)
@JsonDeserialize(using = LocalDateTimeDeserializer.class)
private LocalDateTime ignoreUntil;

provide custom classes:

public class LocalDateTimeSerializer extends JsonSerializer<LocalDateTime> {
    @Override
    public void serialize(LocalDateTime arg0, JsonGenerator arg1, SerializerProvider arg2) throws IOException {
        arg1.writeString(arg0.toString());
    }
}

public class LocalDateTimeDeserializer extends JsonDeserializer<LocalDateTime> {
    @Override
    public LocalDateTime deserialize(JsonParser arg0, DeserializationContext arg1) throws IOException {
        return LocalDateTime.parse(arg0.getText());
    }
}

random fact: if i nest above classes and don't make them static, the error message is weird: org.springframework.web.HttpMediaTypeNotSupportedException: Content type 'application/json;charset=UTF-8' not supported

Answer 2

If you consider using fastjson, you can solve your problem, note the version

 <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>fastjson</artifactId>
        <version>1.2.56</version>
 </dependency>

Answer 3

I had a similar problem while using Spring boot. With Spring boot 1.5.1.RELEASE all I had to do is to add dependency:

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

Answer 4

If you can't use jackson-modules-java8 for whatever reasons you can (de-)serialize the instant field as long using @JsonIgnore and @JsonGetter & @JsonSetter:

public class MyBean {

    private Instant time = Instant.now();

    @JsonIgnore
    public Instant getTime() {
        return this.time;
    }

    public void setTime(Instant time) {
        this.time = time;
    }

    @JsonGetter
    private long getEpochTime() {
        return this.time.toEpochMilli();
    }

    @JsonSetter
    private void setEpochTime(long time) {
        this.time = Instant.ofEpochMilli(time);
    }
}

Example:

@Test
public void testJsonTime() throws Exception {
    String json = new ObjectMapper().writeValueAsString(new MyBean());
    System.out.println(json);
    MyBean myBean = new ObjectMapper().readValue(json, MyBean.class);
    System.out.println(myBean.getTime());
}

yields

{"epochTime":1506432517242}
2017-09-26T13:28:37.242Z

Answer 5

For those who use Spring Boot 2.x

There is no need to do any of the above - Java 8 LocalDateTime is serialised/de-serialised out of the box. I had to do all of the above in 1.x, but with Boot 2.x, it works seamlessly.

See this reference too JSON Java 8 LocalDateTime format in Spring Boot