Date时间

使用jackson对Date类型数据进行处理时候，会自动转换为距离1970年1月1日的毫秒数，如1534128602500，其实是2018-08-13 10:50:02的时间。

import com.fasterxml.jackson.databind.ObjectMapper;
import java.text.SimpleDateFormat;
ObjectMapper mapper = new ObjectMapper();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ssZ");
sdf.setTimeZone(TimeZone.getTimeZone("Asia/Shanghai"));
mapper.setDateFormat(sdf);
byte[] json = mapper.writeValueAsBytes(schema);

在elasticsearch中，对于Date格式的数据，如果不加上上面的格式转换，并且没有事先对elasticsearch中index mapping字段类型进行定义，那么新的字段将会默认是number类型的。

Date datatype
JSON doesn’t have a date datatype, so dates in Elasticsearch can either be:

• strings containing formatted dates, e.g. "2015-01-01" or "2015/01/01 12:10:30".
• a long number representing milliseconds-since-the-epoch.
• an integer representing seconds-since-the-epoch.

Internally, dates are converted to UTC (if the time-zone is specified) and stored as a long number representing milliseconds-since-the-epoch.

Queries on dates are internally converted to range queries on this long representation, and the result of aggregations and stored fields is converted back to a string depending on the date format that is associated with the field.

其他方法，可供参考（未验证）：
1.默认是转成timestamps形式的，通过下面方式可以取消timestamps。

objectMapper.configure(SerializationConfig.Feature.WRITE_DATES_AS_TIMESTAMPS, false);

2. annotaion
   @JsonIgnoreProperties
   @JsonIgnore
   @JsonFormat
   @JsonSerialize
   具体见：https://blog.csdn.net/u013614451/article/details/39699007

3.参考https://www.baeldung.com/jackson-serialize-dates，这里提供了很多方法函数

其他参考
Date format Mapping to JSON Jackson
ElasticSearch Spring-Data Date format always is long

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSXXX");
System.out.println(sdf.parse("2015-08-01T06:51:14.000+08:00"));
Date date = sdf.parse("2015-08-01T06:51:14.000+08:00");


//OffsetDateTime offsetDateTime = LocalDateTime.parse("2018-02-14T06:30").atOffset(ZoneOffset.ofHours(2));
// Uses DateTimeFormatter.ISO_OFFSET_DATE_TIME for which the default format is
// ISO_LOCAL_DATE_TIME followed by the offset ("+HH:mm:ss").
OffsetDateTime offsetDateTime = OffsetDateTime.parse("2019-03-04T03:30:53+08:00");
long dddd = offsetDateTime.getLong(ChronoField.INSTANT_SECONDS);

SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String formatStr =formatter.format(new Date(dddd*1000));
System.out.println(formatStr);