Save and load Guava Optional <?> S in MongoDB using Spring -Data

Question

How to customize the display of Guava Optional(or later JDK8) using Spring -Data-MongoDb?

As an example, the following class should display as json below.

@Data
public class Test
{
    Optional<String> stringOptionalNull    = null;
    Optional<String> stringOptionalAbsent  = Optional.absent();
    Optional<String> stringOptionalPresent = Optional.of("ExampleValue");   
}

Json (Note: null and missing cases are handled in the same way):

{
   "stringOptionalPresent" : "ExampleValue"
}

When they return again in java, nulland absentshould be translated to Optional.absent().

From Spring Data MongoDB Docs I read that org.springframework...Converterthis is the way to go. But with the API, I was not able to process the tags correctly null.

This is the full test version to reproduce the problem. It passes nulland verifies that the loaded object contains only Optional.absent().

public class OptionalMongoDbTest
{
    @Data
    @AllArgsConstructor
    static class ClassWithOptionals
    {
        private final Optional<String> stringOptionalNull;
        private final Optional<String> stringOptionalPresent;
        private final Optional<String> stringOptionalAbsent;
    }

    public static class OptionalToStringConverter<T> implements Converter<Optional<T>, String>
    {
        @Override
        public String convert(final Optional<T> arg0)
        {
            return arg0.isPresent() ? arg0.get().toString() : null;
        }
    }

    public static class StringToOptionalConverter implements Converter<String, Optional<String>>
    {
        @Override
        public Optional<String> convert(final String arg0)
        {
            return Optional.fromNullable(arg0);
        }
    }

    @Test
    public void persisted_object_should_be_equal() throws Exception
    {
        // Setup Mongodb connection
        final SimpleMongoDbFactory mongoDbFactory = new SimpleMongoDbFactory(new Mongo(), "test");
        final MappingMongoConverter converter = new MappingMongoConverter(mongoDbFactory, new MongoMappingContext());

        // Register Custom Converter
        converter.setCustomConversions(new CustomConversions(Arrays.asList(new OptionalToStringConverter(), new StringToOptionalConverter())));
        converter.afterPropertiesSet();

        final MongoTemplate mongoTemplate = new MongoTemplate(mongoDbFactory, converter);
        mongoTemplate.setWriteConcern(WriteConcern.SAFE);

        // Test the mapping
        mongoTemplate.dropCollection(ClassWithOptionals.class);

        final ClassWithOptionals objectToSave = new ClassWithOptionals(null, Optional.of("ExampleValue"), Optional.<String> absent());
        mongoTemplate.save(objectToSave);

        final ClassWithOptionals objectFromMongo = mongoTemplate.findAll(ClassWithOptionals.class).get(0);

        // TODO: That test fails because there are null values comming from the databases
        assertThat(objectFromMongo, is(new ClassWithOptionals(Optional.<String> absent(), Optional.of("ExampleValue"), Optional.<String> absent())));
    }
}

, json, , :

{
    "_id" : ObjectId("5343d8a5e4b0215d78a322d0"),
    "stringOptionalPresent" : "ExampleValue",
    "stringOptionalAbsent" : null // this line should be removed.
}

Edit

, , spring data mongo . - : https://github.com/spring-projects/spring-data-mongodb/blob/master/spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java#L1037-L1041

Answer 1

Spring, , , "" getter :

public Optional<String> getFoo()
{
    return Optional.fromNullable(foo);
}

foo - null, Optional.absent(), .isPresent() false.

Java 8 ( "" Optional Guava) API ; Optional.absent(), Optional.empty(), .fromNullable() .ofNullable().