Java8提供的新的时间类库LocalDateTime用法

╰半夏微凉° 2023-03-13 05:21 2阅读 0赞

Java8提供了LocalDateTime来替代传统的Date来处理时间,如下

1.获取当前时间

@Test
    public void testNow() { 
     LocalDateTime localDateTime = LocalDateTime.now();
     System.out.println(localDateTime);
    }
    
    输出结果:2020-05-06T22:25:07.309

2.根据时间戳初始化时间

@Test
    public void testNewFromTimestamp() { 
     Instant instant = Instant.ofEpochMilli(System.currentTimeMillis());
     LocalDateTime dateTime = LocalDateTime.ofInstant(instant, ZoneId.of("+8"));
     System.out.println(dateTime);
    }
    
    输出结果：2020-05-06T22:27:34.567

3.根据字符串获取时间  
可以使用LocalDateTime.parse方法对字符串进行转化成时间，如果不传pattern，默认是2020-05-06T11:16:12.361格式。

@Test
    public void testNewFromString() { 
    	 // 1.默认格式 2020-05-06T11:16:12.361
    	 String dateStr = "2020-05-06T11:16:12.361";
    	 LocalDateTime localDateTime = LocalDateTime.parse(dateStr);
    	 System.out.println(localDateTime);
    	 // 2. 自定义格式
    	 String pattern = "yyyy-MM-dd HH:mm:ss";
    	 dateStr = "2020-01-01 12:12:12";
    	 localDateTime = LocalDateTime.parse(dateStr, DateTimeFormatter.ofPattern(pattern));
    	 System.out.println(localDateTime);
    }
    
    输出结果：
    2020-05-06T11:16:12.361
    2020-01-01T12:12:12

4.时间转化成字符串  
可以通过DateTimeFormatter的format方法，将LocalDateTime转化成字符串。

@Test
    public void testToString() { 
    	 LocalDateTime now = LocalDateTime.now(ZoneId.of("+8"));
    	 String pattern = "yyyy-MM-dd HH:mm:ss";
    	 DateTimeFormatter formatter = DateTimeFormatter.ofPattern(pattern);
    	 String format = formatter.format(now);
    	 System.out.println(format);
    }
    
    输出结果：2020-05-06 22:33:03

5.LocalDateTime转时间戳

@Test
    public void testDateToTimeMillis() { 
    	 LocalDateTime dateTime = LocalDateTime.now();
    	 long epochMilli = dateTime.toInstant(ZoneOffset.of("+8")).toEpochMilli();
    	 System.out.println(epochMilli);
    }
    
    输出结果：1557153504304

总结:  
DateTimeFormatter是线程安全的，所以在实际使用LocalDateTime的时候，可以把DateTimeFormatter定义成静态常量的方式进行使用。以上列举了比较常用的时间操作，LocalDateTime还可以做很多事情可以自行查阅.

import java.time.Instant;
    import java.time.LocalDateTime;
    import java.time.ZoneOffset;
    import java.time.format.DateTimeFormatter;
    
    public class DateTimeUtils { 
    
     private DateTimeUtils() { 
     }
    
     private final static String COMMON_PATTERN = "yyyy-MM-dd HH:mm:ss";
    
     private final static DateTimeFormatter COMMON_FORMATTER = DateTimeFormatter.ofPattern(COMMON_PATTERN);
    
     private final static ZoneOffset DEFAULT_ZONE_OFFSET = ZoneOffset.of("+8");
    
     /** * 默认 yyyy-MM-dd HH:mm:ss 格式 */
     public static String dateToString(LocalDateTime dateTime) { 
     assert dateTime != null;
     return COMMON_FORMATTER.format(dateTime);
     }
    
     /** * 默认 yyyy-MM-dd HH:mm:ss 格式 */
     public static LocalDateTime stringToDate(String dateStr) { 
     assert dateStr != null;
     return LocalDateTime.parse(dateStr, COMMON_FORMATTER);
     }
    
     public static String dateToString(LocalDateTime dateTime, DateTimeFormatter formatter) { 
     assert dateTime != null;
     return formatter.format(dateTime);
     }
    
     public static LocalDateTime stringToDate(String dateStr, DateTimeFormatter formatter) { 
     assert dateStr != null;
     return LocalDateTime.parse(dateStr, formatter);
     }
    
     public static long dateToTimeMillis(LocalDateTime dateTime) { 
     assert dateTime != null;
     return dateTime.toInstant(DEFAULT_ZONE_OFFSET).toEpochMilli();
     }
    
     public static LocalDateTime timeMillisToDate(long timeMillis) { 
     Instant instant = Instant.ofEpochMilli(timeMillis);
     return LocalDateTime.ofInstant(instant, DEFAULT_ZONE_OFFSET);
     }
    
     public static void main(String[] args) { 
     String s = dateToString(LocalDateTime.now());
     System.out.println(s);
     System.out.println();
     String dateStr = "2019-01-01 12:12:12";
     LocalDateTime localDateTime = stringToDate(dateStr);
     System.out.println(localDateTime);
     System.out.println();
     System.out.println(dateToTimeMillis(localDateTime));
     System.out.println();
     System.out.println(timeMillisToDate(System.currentTimeMillis()));
     }
    }