[Java知识库]LocalDateTime、LocalDate、Date的相互转换及与String类型的相互转换

目录

前言：LocalDateTime 及 LocalDate 是 Java8 的新特性，有时为了兼容 Date 类型需要进行转换，以及与String之间的相互转换。

LocalDateTime 转 LocalDate:

LocalDateTime localDateTime = LocalDateTime.now();
LocalDate localDate = localDateTime.toLocalDate();

LocalDateTime 转 Date

在LocalDateTime 转 Date 时，需要使用到 Java 8的几个类：

• ZoneId/ZoneOffset：表示时区
• ZonedDateTime： 表示特定时区的日期和时间
• Instant：表示时刻，不直接对应年月日信息，需要通过时区转换

LocalDateTime localDateTime = LocalDateTime.now();
//获取系统默认时区
ZoneId zoneId = ZoneId.systemDefault();
//时区的日期和时间
ZonedDateTime zonedDateTime = localDateTime.atZone(zoneId);
//获取时刻
Date date = Date.from(zonedDateTime.toInstant());
System.out.println("格式化前：localDateTime:" + localDateTime + "  Date:" + date);
//格式化LocalDateTime、Date
DateTimeFormatter localDateTimeFormat = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
System.out.println("格式化后：localDateTime:" + localDateTimeFormat.format(localDateTime) 
                + "  Date:" + dateFormat.format(date));

输出结果如下：

格式化前：localDateTime:2020-10-27T11:35:09.969  Date:Tue Oct 27 11:35:09 CST 2020
格式化后：localDateTime:2020-10-27 11:35:09  Date:2020-10-27 11:35:09

LocalDate 转 LocalDateTime

LocalDate localDate = LocalDate.now();
LocalDateTime localDateTime1 = localDate.atStartOfDay();
LocalDateTime localDateTime2 = localDate.atTime(8,8,8);
LocalDateTime localDateTime3 = localDate.atTime(LocalTime.now());

LocalDate 转 Date

LocalDate localDate = LocalDate.now();
ZoneId zoneId = ZoneId.systemDefault();
Date date = Date.from(localDate.atStartOfDay().atZone(zoneId).toInstant());

Date 转 LocalDateTime

Date date = new Date();
ZoneId zoneId = ZoneId.systemDefault();
LocalDateTime localDateTime = date.toInstant().atZone(zoneId).toLocalDateTime();

Date 转 LocalDate

Date date = new Date();
ZoneId zoneId = ZoneId.systemDefault();
LocalDate localDate = date.toInstant().atZone(zoneId).toLocalDate();

LocalDateTime、LocalDate、Date 转String

//Date转String
Date date = new Date();
//常见使用格式：yyyy-MM-dd hh:mm:ss ； yyyy/MM/dd;yyyy年MM月dd日；yyyy-MM
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
String dateString = sdf.format(date);

//LocalDateTime转String
LocalDateTime localDateTime = LocalDateTime.now();
DateTimeFormatter dtf1 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
String localDateTimeString = dtf1.format(localDateTime);

//LocalDate转String
LocalDate localDate = LocalDate.now();
DateTimeFormatter dtf2 = DateTimeFormatter.ofPattern("yyyy-MM-dd");
String localDateString = dtf2.format(localDate);

String 转 Date、LocalDateTime、LocalDate

//String转Date
String dateString = "2021-9-22 08:08:08";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
Date date = sdf.parse(dateString);

//String转LocalDateTime
String localDateTimeString = "2021-9-22 08:08:08";
DateTimeFormatter dtf1 = ofPattern("yyyy-MM-dd hh:mm:ss");
LocalDateTime localDateTime = LocalDateTime.parse(localDateTimeString, dtf1);

//String转LocalDate
String localDateString = "2021-9-22";
DateTimeFormatter dtf2 = ofPattern("yyyy-MM-dd");
LocalDate localDate = LocalDate.parse(localDateString, dtf2);