由于java版本的迭代，一个使用java开发的项目中可能出现多种日期对象，例如LocalDateTime、LocalDate、Date，不像C#只有一个DateTime，因此在各种日期格式或者对象之间的转换显得有点复杂，总是记不住，在需要用到时总是需要依靠搜索引擎，有点浪费时间，所以特意把常用的转换场景总结如下：

1、LocalDateTime转为String、TimeStamp、Long、Instant、 Date

System.out.println("----------------LocalDateTime----------------");

// LocalDateTime -> String
String localDateTimeToString = LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
System.out.println("LocalDateTime -> String:  " + localDateTimeToString);

// LocalDateTime -> TimeStamp
Timestamp localDateTimeToTimeStamp = Timestamp.valueOf(LocalDateTime.now());
System.out.println("LocalDateTime -> TimeStamp:  " + localDateTimeToTimeStamp);

// LocalDateTime -> Long
Long localDateTimeToLong = Timestamp.valueOf(LocalDateTime.now()).getTime();
System.out.println("LocalDateTime -> Long:  " + localDateTimeToLong);

// LocalDateTime -> Instant
Instant localDateTimeToInstant = LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant();
System.out.println("LocalDateTime -> Instant:  " + localDateTimeToInstant);

// LocalDateTime -> Date
Date LocalDateTimeToDate = Date.from(LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant());
System.out.println("LocalDateTime -> Date:  " + LocalDateTimeToDate);

2、String转为LocalDateTime、 Date

System.out.println("----------------String----------------");

// String -> LocalDateTime
LocalDateTime stringToLocalDateTime =LocalDateTime.parse("2018-03-11 15:30:11", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
System.out.println("String -> LocalDateTime:  " + stringToLocalDateTime);

// String -> Date
try {
    Date stringToDate = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").parse("2018-03-11 15:30:11");
    System.out.println("String -> Date:  " + stringToDate);
} catch (ParseException ex) {
 
}

3、Timestamp转为LocalDateTime、 Date

System.out.println("---------------Timestamp-----------------");

// Timestamp -> LocalDateTime
LocalDateTime timeStampToLocalDateTime =
        LocalDateTime.ofInstant(new Timestamp(1520754566856L).toInstant(), ZoneId.systemDefault());
System.out.println("Timestamp -> LocalDateTime:  " + timeStampToLocalDateTime);

// Timestamp -> Date
Date timestampToDate = Date.from(new Timestamp(1520754566856L).toInstant());
System.out.println("Timestamp -> Date:  " + timestampToDate);

4、Long转为LocalDateTime、 Date

System.out.println("---------------Long-----------------");

// Long -> LocalDateTime
LocalDateTime longToLocalDateTime =
        LocalDateTime.ofInstant(Instant.ofEpochMilli(1520754566856L), ZoneId.systemDefault());
System.out.println("Long -> LocalDateTime:  " + longToLocalDateTime);

// Long -> Date
Date longToDate = new Date(1520754566856L);
System.out.println("Long -> Date: " + longToDate);

5、Instant转为LocalDateTime、 Date

System.out.println("----------------Instant----------------");

// Instant -> LocalDateTime
LocalDateTime instantToLocalDateTime = LocalDateTime.ofInstant(Instant.now(), ZoneId.systemDefault());
System.out.println("Instant -> LocalDateTime:  " + instantToLocalDateTime);

// Instant -> Date
Date instantToDate = Date.from(Instant.now());
System.out.println("Instant -> Date:  " + instantToDate);

6、Date转为LocalDateTime、String、TimeStamp、Long、Instant

System.out.println("----------------Date----------------");

// Date -> String
String dateToString = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
System.out.println("Date -> String:  " + dateToString);

// Date -> LocalDateTime
LocalDateTime dateToLocalDateTime = LocalDateTime.ofInstant(new Date().toInstant(), ZoneId.systemDefault());
System.out.println("Date -> LocalDateTime:  " + dateToLocalDateTime);

// Date -> Timestamp
Timestamp dateToTimestamp = new Timestamp(new Date().getTime());
System.out.println("Date -> Timestamp:  " + dateToTimestamp);

// Date -> Long
Long dateToLong = new Date().getTime();
System.out.println("Date -> Long: " + dateToLong);

// Date -> Instant
Instant dateToInstant = new Date().toInstant();
System.out.println("Date -> Instant:  " + dateToInstant);

Q.E.D.