JaVersConfiguration.java

import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import org.javers.core.ChangesByCommit;
import org.javers.core.diff.Change;
import org.javers.core.json.BasicStringTypeAdapter;
import org.javers.core.json.typeadapter.util.UtilTypeCoreAdapters;
import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilderCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import java.time.Instant;
import java.time.temporal.ChronoField;
import java.util.List;

@Configuration
public class JaVersConfiguration {

    @Bean
    InstantTruncatedTypeAdapter instantTruncatedTypeAdapter() {
        return new InstantTruncatedTypeAdapter();
    }

    /**
     * The Jackson2ObjectMapperBuilder context can be customized by one or more Jackson2ObjectMapperBuilderCustomizer beans.
     * Such customizer beans can be ordered (the Boot customizer has an order of 0), letting additional customization
     * be applied both before and after the Boot customization.
     */
    @Bean
    Jackson2ObjectMapperBuilderCustomizer jacksonJaVersCustomizer() {
        return (Jackson2ObjectMapperBuilder jacksonObjectMapperBuilder) ->
                jacksonObjectMapperBuilder
                        .mixIn(ChangesByCommit.class, JaVersChangesMixIn.class)
                        .mixIn(Change.class, ClassNameTypeMixIn.class);
    }
    
    /**
     * Truncated to microseconds {@link Instant} type adapter.
     * Instant precision is 9 while PostgreSQL timestamp precision is 6 (rounded).
     * See {@link org.javers.java8support.InstantTypeAdapter}.
     */
    static class InstantTruncatedTypeAdapter extends BasicStringTypeAdapter<Instant> {
        @Override
        public String serialize(Instant sourceValue) {
            return UtilTypeCoreAdapters.serialize(sourceValue
                    .with(ChronoField.MICRO_OF_SECOND,
                            Math.round((double) sourceValue.get(ChronoField.NANO_OF_SECOND) / 1000)));
        }

        @Override
        public Instant deserialize(String serializedValue) {
            return UtilTypeCoreAdapters.deserializeToInstant(serializedValue);
        }

        @Override
        public Class<?> getValueType() {
            return Instant.class;
        }

    }

    /**
     * Makes `changes` returned by non-standard `get()` method serializable by Jackson.
     */
    abstract static class JaVersChangesMixIn {
        @JsonProperty("changes")
        abstract List<Change> get();
    }

    /**
     * Instructs Jackson to serialize class name as `type` attribute.
     * Useful for JaVers Change subclasses, especially org.javers.core.diff.changetype.NewObject.
     */
    @JsonTypeInfo(use = JsonTypeInfo.Id.SIMPLE_NAME, property = "type")
    abstract static class ClassNameTypeMixIn {
    }

}

InstantTruncatedTypeAdapter - Java Instant precision is 9 while PostgreSQL timestamp precision is 6 (rounded). As the result, JaVers reports created Instant as updated for an update after an insert (which JaVers records with nanos).

• repository.save(entity) is called for a new entity
  • new Instant value with nanos is generated by @org.springframework.data.annotation.CreatedDate annotation processor
  • JaVers intercepts the entity.created value passed to repository.save(entity)
  • actual value stored in the PostgreSQL is set to rounded micros
• repository.findById(id) is called to retrieve an entity
  • entity is returned with entity.created set to rounded micros (as retrieved from PostgreSQL)
• an entity property is modified (e.g. name) and repository.save(entity) is called for an updated entity
• JaVers intercepts the entity.created value passed repository.save(entity)
  • JaVers reports the entity.created value changed because the insert save call contained nanos and a subsequent update save call contained rounded micros retrieved from PostgreSQL