java8 Date LocalDate LocaDateTime 互相转化

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：

    @Test

    public void method3(){

        LocalDateTime localDateTime  = LocalDateTime.now();

        System.out.println("localDateTime: "+localDateTime);

        Instant instant =  localDateTime.atZone(ZoneId.systemDefault()).toInstant();

        Date date = Date.from(instant);

        System.out.println("date: "+date);

    }

输出结果

localDateTime: 2018-11-19T10:22:00.712

date: Mon Nov 19 10:22:00 CST 2018

LocalDateTime---------->Date

    @Test

    public void method4(){

        LocalDate localDate = LocalDate.now();

        System.out.println("localDate: "+localDate);

        Instant instant =  localDate.atStartOfDay(ZoneId.systemDefault()).toInstant();

        Date date = Date.from(instant);

        System.out.println("date: "+date);

    }

输出结果

localDate: 2018-11-19

date: Mon Nov 19 00:00:00 CST 2018

LocalDate------->Date

    @Test

    public void method5(){

        LocalDateTime localDateTime = LocalDateTime.now();

        LocalDate localDate = localDateTime.toLocalDate();

        System.out.println(localDate);

    }

    @Test

    public void method6(){

        LocalDate localDate = LocalDate.now();

        LocalDateTime localDateTime = localDate.atStartOfDay();

        System.out.println(localDateTime);

    }

LocalDate LocalDateTime

    @Test

    public void method1(){

        Date d1 = new Date();

        System.out.println("date: "+d1);

        Instant instant =  d1.toInstant();

        LocalDateTime local1 = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());

        System.out.println("LocalDateTime: "+local1);

    }

输出结果

date: Mon Nov 19 09:37:14 CST 2018

LocalDateTime: 2018-11-19T09:37:14.063

Date ----->LocalDateTime

    @Test

    public void method2(){

        Date d1 = new Date();

        System.out.println("date: "+d1);

        Instant instant =  d1.toInstant();

        LocalDateTime ldt = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());

        LocalDate ld = ldt.toLocalDate();

        System.out.println("LocalDate: "+ld);

    }

输出结果

date: Mon Nov 19 09:46:30 CST 2018

LocalDate: 2018-11-19

Date ------>LocalDate

巴特西

java8 Date LocalDate LocaDateTime 互相转化

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