Java 8 Date/Time (JSR-310) types mapping with Spring Data MongoDB

Question

I have simple document with Java 8 date/time fields

@Document
public class Token {
    private Instant createdAt;
    ...
}

that I want to persist with Spring Data MongoDB version 1.5. But fields of type java.time.Instant could not be de-serialized correctly because MappingMongoConverter lacks converters for java.time classes.

In Spring 4 I found org.springframework.format.datetime.standard.DateTimeConverters with different Converters including InstantToLongConverter and LongToInstantConverter declared as private static classes.

How can I configure MongoTemplate to use them to map Instant fields to longs?

Answer 1

I don't know if this is the best way but I added Java 8 Date/Time (JSR-310) types support to Spring Data MongoDB 1.5.0.RELEASE like this:

1. First step. Add simple Spring Converters

   public class InstantToLongConverter implements Converter<Instant, Long> {
       @Override
       public Long convert(Instant instant) {
           return instant.toEpochMilli();
       }
   }
   
   public class LongToInstantConverter implements Converter<Long, Instant> {
       @Override
       public Instant convert(Long source) {
           return Instant.ofEpochMilli(source);
       }
   }
   
   public class LocalDateToStringConverter implements Converter<LocalDate, String> {
       @Override
       public String convert(LocalDate localDate) {
           return localDate.toString();
       }
   }
   
   public class StringToLocalDateConverter implements Converter<String, LocalDate> {
       @Override
       public LocalDate convert(String source) {
           return LocalDate.parse(source);
       }
   }
   

2. Second step. Register these custom Converters with MappingMongoConverter in your AbstractMongoConfiguration implementation like this:

   @Configuration
   @EnableMongoRepositories(basePackages = {"my.app.repository"})
   public class MongoConfiguration extends AbstractMongoConfiguration {
   
       ...
   
       @Override
       public CustomConversions customConversions() {
           return new CustomConversions(Arrays.asList(
                   new InstantToLongConverter(), new LongToInstantConverter(),
                   new LocalDateToStringConverter(), new StringToLocalDateConverter()));
       }
   }
   

Now your document's Instant fields will be persisted as long values and LocalDates as Strings.