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Jackson's preface to serialization and deserialization of Java8 time types

By default, the new time types of Jackson serialization / deserialization Java8 are not serialized into strings or timestamps, because there is no corresponding serialization policy, so we can configure the serialization and deserialization policies of objects ourselves, or we can refer to jackson-datatype-jsr310 's jar package for processing. Let's take LocalDateTime as an example.

Introduce JSR310 dependency

Within the project, we refer to the dependency

Com.fasterxml.jackson.datatype jackson-datatype-jsr310 2.8.11JSR310 default configuration

By default, JSR310 provides us with serialization / deserialization classes that are converted to strings, which are LocalDateTimeSerializer/LocalDateTimeDeserializer, which we can serialize using the existing implementation.

We register a JavaTimeModule module provided by JSR310 in the ObjectMapper of Jackson. In JavaTimeModule, we need to configure the serialization policy of LocalDateTime. The specific code is as follows

ObjectMapper objectMapper = new ObjectMapper (); JavaTimeModule javaTimeModule = new JavaTimeModule (); javaTimeModule.addSerializer (LocalDateTime.class,new LocalDateTimeSerializer (DateTimeFormatter.ofPattern ("yyyy-MM-dd HH:mm:ss") .addroomializer (LocalDateTime.class,new LocalDateTimeDeserializer (DateTimeFormatter.ofPattern ("yyyy-MM-dd HH:mm:ss")); objectMapper.registerModule (javaTimeModule); Custom configuration serialization / deserialization of Java8 time types

This time, we customize the conversion to a second timestamp. Jackson provides two abstract classes, JsonDeserializer and JsonSerializer, which are the parents of deserialization and serialization, respectively. We inherit it and implement the abstract method. The specific code is as follows

Public class InstantSerializer extends JsonSerializer {@ Override public void serialize (LocalDateTime value, JsonGenerator gen, SerializerProvider serializers) throws IOException, JsonProcessingException {gen.writeNumber (DateUtils.toSecond (value));}} public class InstantDeserializer extends JsonDeserializer {@ Override public LocalDateTime deserialize (JsonParser p, DeserializationContext txt) throws IOException, JsonProcessingException {return Instant.ofEpochSecond (p.getLongValue ()) .atZone (ZoneId.systemDefault ()). ToLocalDateTime ();}}

Register the defined serialization specification with ObjectMapper

ObjectMapper objectMapper = new ObjectMapper (); JavaTimeModule javaTimeModule = new JavaTimeModule (); javaTimeModule.addSerializer (LocalDateTime.class,new InstantSerializer ()) .addroomializer (LocalDateTime.class,new InstantDeserializer ()); objectMapper.registerModule (javaTimeModule); Summary

At this point, we have roughly introduced two methods of configuration, one is already provided by jsr310, and the other is implemented by ourselves by inheriting the abstract classes provided by jackson. The two are similar in implementation, but they are more flexible and controllable through inheritance, and it is more convenient to use jsr310.

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