Java 8 中 Date与LocalDateTime、LocalDate、LocalTime互转

叁歲伎倆 2022-03-27 03:46 172阅读 0赞

> 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.
    //从即时对象中获取日期的实例。新时间转旧时间用到
    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.
    //将此日期对象转换为一个瞬间。旧时间转新时间用到
    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 UDateToLocalDateTime() { 
        java.util.Date date = new java.util.Date();
        Instant instant = date.toInstant();
        ZoneId zone = ZoneId.systemDefault();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
    }
    
    // 02. java.util.Date --> java.time.LocalDate
    public void UDateToLocalDate() { 
        java.util.Date date = new java.util.Date();
        Instant instant = date.toInstant();
        ZoneId zone = ZoneId.systemDefault();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
        LocalDate localDate = localDateTime.toLocalDate();
    }
    
    // 03. java.util.Date --> java.time.LocalTime
    public void UDateToLocalTime() { 
        java.util.Date date = new java.util.Date();
        Instant instant = date.toInstant();
        ZoneId zone = ZoneId.systemDefault();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, zone);
        LocalTime localTime = localDateTime.toLocalTime();
    }
    
    
    // 04. java.time.LocalDateTime --> java.util.Date
    public void LocalDateTimeToUdate() { 
        LocalDateTime localDateTime = LocalDateTime.now();
        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDateTime.atZone(zone).toInstant();
        java.util.Date date = Date.from(instant);
    }
    
    
    // 05. java.time.LocalDate --> java.util.Date
    public void LocalDateToUdate() { 
        LocalDate localDate = LocalDate.now();
        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDate.atStartOfDay().atZone(zone).toInstant();
        java.util.Date date = Date.from(instant);
    }
    
    // 06. java.time.LocalTime --> java.util.Date
    public void LocalTimeToUdate() { 
        LocalTime localTime = LocalTime.now();
        LocalDate localDate = LocalDate.now();
        LocalDateTime localDateTime = LocalDateTime.of(localDate, localTime);
        ZoneId zone = ZoneId.systemDefault();
        Instant instant = localDateTime.atZone(zone).toInstant();
        java.util.Date date = Date.from(instant);
    }

> 参考：[https://www.cnblogs.com/exmyth/p/6425878.html][https_www.cnblogs.com_exmyth_p_6425878.html]

[https_www.cnblogs.com_exmyth_p_6425878.html]: https://www.cnblogs.com/exmyth/p/6425878.html