sprint data elasticsearch rest client无法处理localdatetime格式的问题

在使用HighLevelRestClient的时候，如果Document对象有LocalDateTime类的属性，那么在搜索结果转换为对象的时候就会报错，无法将long型转换为localdatetime，这时因为默认的elasticsearch converters里面不提供，所以需要我们自己添加。

@Configuration
public class ESConfiguration extends AbstractElasticsearchConfiguration {

    @Value("${elasticsearch.config.hosts}")
    private String hosts;

    @Bean
    public RestHighLevelClient elasticsearchClient() {
        ClientConfiguration configuration = ClientConfiguration.builder()
                .connectedTo(this.hosts)
                .build();

        return RestClients.create(configuration).rest();
    }

    @Bean
    @Override
    public EntityMapper entityMapper() {

        ElasticsearchEntityMapper entityMapper = new ElasticsearchEntityMapper(
                elasticsearchMappingContext(), new DefaultConversionService()
        );
        entityMapper.setConversions(elasticsearchCustomConversions());

        return entityMapper;
    }

    /**
     * 默认的converter不支持long到localdatime的转换，从elasticsearch读取的时候会报错，所以在这里添加一个。
     */
    @Bean
    @Override
    public ElasticsearchCustomConversions elasticsearchCustomConversions() {
        List<Converter> converters= new ArrayList<>();
        converters.add(LongToLocalDateTimeConverter.INSTANCE);
        return new ElasticsearchCustomConversions(converters);
    }

    @ReadingConverter
    static enum LongToLocalDateTimeConverter implements Converter<Long, LocalDateTime> {
        INSTANCE;

        private LongToLocalDateTimeConverter() {
        }

        public LocalDateTime convert(Long source) {
            return Instant.ofEpochMilli(source).atZone(ZoneId.systemDefault()).toLocalDateTime();
        }
    }
}