I wrote this little bit of code for all 4 of these conversion options:

• DateToLocalDateTimeConverter
• DateToLocalDateConverter
• LocalDateTimeToDateConverter
• LocalDateToDateConverter

Here is an example

public class DateToLocalDateTimeConverter implements Converter<Date, LocalDateTime> {

    @Override 
    public LocalDateTime convert(Date source) { 
        return source == null ? null : LocalDateTime.ofInstant(source.toInstant(), ZoneId.systemDefault()); 
    }
}

Then by including this in the xml configuration for the mongodb connection I was able to work in java 8 dates with mongodb (remember to add all the converters):

<mongo:mapping-converter>
    <mongo:custom-converters>
        <mongo:converter>
            <bean class="package.DateToLocalDateTimeConverter" />
        </mongo:converter>
    </mongo:custom-converters>
</mongo:mapping-converter>