Java 8 中 Date与LocalDateTime、LocalDate、LocalTime互转

Java 8中 java.util.Date 类新增了两个方法，分别是from(Instant instant)和toInstant()方法
// Obtains an instance of Date from an Instant object.

public static Date from(Instant instant) {
    try {
        return new Date(instant.toEpochMilli());
    } catch (ArithmeticException ex) {
        throw new IllegalArgumentException(ex);
    }
}

// Converts this Date object to an Instant.

public Instant toInstant() {
    return Instant.ofEpochMilli(getTime());
}

这两个方法使我们可以方便的实现将旧的日期类转换为新的日期类，具体思路都是通过Instant当中介，然后通过Instant来创建LocalDateTime（这个类可以很容易获取LocalDate和LocalTime），新的日期类转旧的也是如此，将新的先转成LocalDateTime，然后获取Instant，接着转成Date，具体实现细节如下：

// 01. java.util.Date --> java.time.LocalDateTime

public void DateToLocalDateTime() {
        Date date = new Date();
        Instant instant = date.toInstant();
        ZoneId zoneId = ZoneId.systemDefault();
//        LocalDateTime localDateTime = instant.atZone(zoneId).toLocalDateTime();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zoneId);
        System.out.println(localDateTime);
    }

// 02. java.util.Date --> java.time.LocalDate

public void DateToLocalDate() {
        Date date = new Date();
        Instant instant = date.toInstant();
        ZoneId zoneId = ZoneId.systemDefault();
//        LocalDateTime localDateTime = instant.atZone(zoneId).toLocalDateTime();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zoneId);
        LocalDate localDate = localDateTime.toLocalDate();
        System.out.println(localDate);
    }

// 03. java.util.Date --> java.time.LocalTime

public void DateToLocalTime() {
        Date date = new Date();
        Instant instant = date.toInstant();
        ZoneId zoneId = ZoneId.systemDefault();
//        LocalDateTime localDateTime = instant.atZone(zoneId).toLocalDateTime();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zoneId);
        LocalTime localTime = localDateTime.toLocalTime();
        System.out.println(localTime);
    }

// 04. java.time.LocalDateTime --> java.util.Date

public void LocalDateTimeToDate() {
        LocalDateTime localDateTime = LocalDateTime.now();
        ZoneId zoneId = ZoneId.systemDefault();
        Instant instant = localDateTime.atZone(zoneId).toInstant();
        Date date = Date.from(instant);
        System.out.println(date);
    }

// 05. java.time.LocalDate --> java.util.Date

public void LocalDateToDate() {
        LocalDate localDate = LocalDate.now();
        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDate.atStartOfDay().atZone(zone).toInstant();
        Date date = Date.from(instant);
        System.out.println(date);
    }

// 06. java.time.LocalTime --> java.util.Date

public void LocalTimeToDate() {
        LocalTime localTime = LocalTime.now();
        LocalDate localDate = LocalDate.now();
        LocalDateTime localDateTime = LocalDateTime.of(localDate, localTime);
        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDateTime.atZone(zone).toInstant();
        Date date = Date.from(instant);
        System.out.println(date);
    }