Java基础：JDK 8 之 LocalDate,LocalTime,LocalDateTime 使用

因为 Date 实在不方便，特别是在日期计算时难用，并且格式化是非线程安全的。

JDK 8 提供 LocalDate, LocalTime, LocalDateTime 可以更方便操作日期时间，是线程安全的。

在 JDK 8 出来之前，大多会使用第三方库 Joda 来操作日期时间，GitHub joda-time。

国内工具类 Hutool 也提供了日期时间工具类，可以方便操作。

LocalDate

1. LocalDate，LocalTime，LocalDateTime

   import java.time.*;
   import java.time.format.DateTimeFormatter;
   import java.time.temporal.ChronoField;
   import java.time.temporal.ChronoUnit;
   
   public class LocalDateDemo {
   
       public static void main(String[] args) {
   
           //2019-10-30
           LocalDate localDate = LocalDate.now();
           //2019-09-10
           LocalDate localDate1 = LocalDate.of(2019, 9, 10);
           //2019-10-30T19:58:29.519
           LocalDateTime localDateTime = LocalDateTime.now();
           //19:58:29.520
           LocalTime localTime = LocalTime.now();
   
           //获取年:2019
           int year = localDate.getYear();
           //获取年:2019
           int year1 = localDate.get(ChronoField.YEAR);
           //获取月:OCTOBER
           Month month = localDate.getMonth();
           //获取月:10
           int month1 = localDate.get(ChronoField.MONTH_OF_YEAR);
           //获取天:30
           int day = localDate.getDayOfMonth();
           //获取天:30
           int day1 = localDate.get(ChronoField.DAY_OF_MONTH);
           //获取星期:WEDNESDAY
           DayOfWeek dayOfWeek = localDate.getDayOfWeek();
           int dayOfMonth = localDate.getDayOfMonth();
           int dayOfYear = localDate.getDayOfYear();
           //获取星期:3
           int dayOfWeek1 = localDate.get(ChronoField.DAY_OF_WEEK);
   
           /**
            * LocalDateTime
            * 获取年月日时分秒，等于LocalDate+LocalTime
            */
           //2019-10-30T20:01:30.666
           LocalDateTime localDateTime0 = LocalDateTime.now();
           //2019-09-10T14:46:56
           LocalDateTime localDateTime1 = LocalDateTime.of(2019, Month.SEPTEMBER, 10, 14, 46, 56);
           //2019-10-30T20:01:30.665
           LocalDateTime localDateTime2 = LocalDateTime.of(localDate, localTime);
           //2019-10-30T20:01:30.665
           LocalDateTime localDateTime3 = localDate.atTime(localTime);
           //2019-10-30T20:01:30.665
           LocalDateTime localDateTime4 = localTime.atDate(localDate);
   
           /**
            * 获取LocalDate
            */
           //2019-10-30
           LocalDate localDate2 = localDateTime.toLocalDate();
   
           /**
            * 获取LocalTime
            */
           //20:03:45.084
           LocalTime localTime2 = localDateTime.toLocalTime();
   
           /**
            * 获取秒数
            */
           Instant instant = Instant.now();
           //秒数:1572437086
           long currentSecond = instant.getEpochSecond();
           //毫秒:1572437086198
           long currentMilli = instant.toEpochMilli();
           long nowMilli = System.currentTimeMillis();//更方便
   
           /**
            * 日期计算
            */
           //2019-09-10T14:46:56
           LocalDateTime localDateTime11 = LocalDateTime.of(2019, Month.SEPTEMBER, 10,
                   14, 46, 56);
           //增加一年:2020-09-10T14:46:56
           LocalDateTime localDateTime12 = localDateTime11.plusYears(1);
           //增加一年:2020-09-10T14:46:56
           LocalDateTime localDateTime13 = localDateTime11.plus(1, ChronoUnit.YEARS);
           //减少一个月:2019-08-10T14:46:56
           LocalDateTime localDateTime14 = localDateTime11.minusMonths(1);
           //减少一个月:2019-08-10T14:46:56
           LocalDateTime localDateTime15 = localDateTime11.minus(1, ChronoUnit.MONTHS);
   
           /**
            * 通过With修改值
            */
           //修改年2020:2020-10-30T20:11:54.369
           LocalDateTime localDateTime16 = localDateTime.withYear(2020);
           //修改为2022:2022-10-30T20:11:54.369
           LocalDateTime localDateTime17 = localDateTime.with(ChronoField.YEAR, 2022);
   
           /**
            * 格式化时间
            */
           //2019-09-10
           LocalDate localDate11 = LocalDate.of(2019, 9, 10);
           //20191030
           String s1 = localDate.format(DateTimeFormatter.BASIC_ISO_DATE);
           //2019-10-30
           String s2 = localDate.format(DateTimeFormatter.ISO_LOCAL_DATE);
           //自定义格式化
           DateTimeFormatter dateTimeFormatter =   DateTimeFormatter.ofPattern("dd/MM/yyyy");
           //30/10/2019
           String s3 = localDate.format(dateTimeFormatter);
   
           //解析时间
           //2019-09-10
           LocalDate localDate12 = LocalDate.parse("20190910", DateTimeFormatter.BASIC_ISO_DATE);
           //2019-09-10
           LocalDate localDate13= LocalDate.parse("2019-09-10", DateTimeFormatter.ISO_LOCAL_DATE);
   
       }
   }

入参与出参

这种方式在入参时，根据需要格式添加日期时间格式化注解（@DateTimeFormat），灵活。

@JsonDeserialize(using = LocalDateTimeDeserializer.class)  //application/json
@JsonSerialize(using = LocalDateTimeSerializer.class) //application/json
@DateTimeFormat(pattern = "yyyy-MM-dd")//入参转换,对 form 或 url 传进来的起效
@JsonFormat(shape=JsonFormat.Shape.STRING, pattern="yyyy/MM/dd")//输出转换
private LocalDate birthday;

但如果能统一日期或时间的入参格式，且不想在每个属性上添加日期格式化注解，则可以自定义转换器，并注册为 Bean，就可自动将日期或时间格式化传入，如下：

@Configuration
public class LocalDateTimeConverter {

    @Bean
    public Converter<String, LocalDate> localDateConverter() {
        return new Converter<String, LocalDate>() {
            @Override
            public LocalDate convert(String source) {
                return LocalDate.parse(source, DateTimeFormatter.ofPattern("yyyy-MM-dd"));
            }
        };
    }

    @Bean
    public Converter<String, LocalDateTime> localDateTimeConverter() {
        return new Converter<String, LocalDateTime>() {
            @Override
            public LocalDateTime convert(String source) {
                return LocalDateTime.parse(source, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
            }
        };
    }
}

其它参考

1. SpringMvc Json LocalDateTime 互转,form urlencoded @ModelAttribute 转换