Java日期处理

作者: Tinyspot | 来源:发表于2022-08-15 07:40 被阅读0次

1. 日期时间

1.1 TimeZone 时区

格林威治标准时间 GMT+08:00
UTC+08:00
夏令时 DST
Asia/Shanghai

1.2 如何存储时间

Epoch Time : 从 1970年1月1日零点（格林威治时区/GMT+00:00）到现在经历的秒数，例：北京 2016-11-20 8:15:01 = 1479600901
Java 中用 long 类型的整型表示毫秒数, 北京 2016-11-20 8:15:01.123 = 1479600901123

2. 日期 API

java.util.Data
java.util.Calendar

2.1 Date

java.util.Date 类中的大部分方法已被 Calendar 类方法取代
new Date()
long getTime()
toGMTString()
toLocaleString()

// Params: date – the milliseconds since January 1, 1970, 00:00:00 GMT.
public Date(long date) {
  fastTime = date;
}

private static final long ONE_DAY_MILLISECONDS = 1000 * 60 * 60 * 24;

public static void main(String[] args) {
    Date today = new Date();
    // today.toString() // Fri Aug 05 09:44:07 CST 2022
    System.out.println(today.toLocaleString());

    // Date(long date /* the milliseconds */)
    // 昨天 = 今天 减去 一天的毫秒值
    Date yesterday = new Date(today.getTime() - 24 * 60 * 60 * 1000);
    System.out.println(yesterday.toLocaleString());
}

2.2 Calendar

public abstract class Calendar implements Serializable, Cloneable, Comparable<Calendar> {

  // JANUARY which is 0
  public final static int MONTH = 2;

  // HOUR is used for the 12-hour clock (0 - 11)
  // HOUR_OF_DAY is used for the 24-hour
  public final static int HOUR_OF_DAY = 11;

  public static Calendar getInstance() {
      return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * field – the given calendar field.
   * value – the value to be set for the given calendar field.
   */
  public void set(int field, int value) {}

  public final void set(int year, int month, int date, int hourOfDay, int minute, int second) {
    set(YEAR, year);
    set(MONTH, month);
    set(DATE, date);
    set(HOUR_OF_DAY, hourOfDay);
    set(MINUTE, minute);
    set(SECOND, second);
  }
}

get(...) 获取时间

Calendar calendar = Calendar.getInstance();
Date time = calendar.getTime();
System.out.println(calendar.getTime().toLocaleString());
System.out.println(calendar.getTimeInMillis());

int year = calendar.get(Calendar.YEAR);
int month = calendar.get(Calendar.MONTH);
int day = calendar.get(Calendar.DAY_OF_MONTH);
int hour = calendar.get(Calendar.HOUR_OF_DAY);
int minute = calendar.get(Calendar.MINUTE);
int second = calendar.get(Calendar.SECOND);
// 月份从 0 开始，要 +1
System.out.println(year + "-" + (month + 1) + "-" + day + " " + hour + ":" + minute + ":" + second);

set(...) 修改时间

Calendar calendar = Calendar.getInstance();
calendar.set(Calendar.DAY_OF_MONTH, 5);
System.out.println(calendar.getTime().toLocaleString());

add(..) 修改时间

Calendar calendar = Calendar.getInstance();
// 后一小时
calendar.add(Calendar.HOUR_OF_DAY, 1);
// 前一小时
calendar.add(Calendar.HOUR_OF_DAY, -1);

最大最小值

Calendar calendar = Calendar.getInstance();
int minimum = calendar.getActualMinimum(Calendar.DAY_OF_MONTH);
int maximum = calendar.getActualMaximum(Calendar.DAY_OF_MONTH);

3. SimpleDateFormat

查看 SimpleDateFormat 源码注释文档

Letter	Date or Time Component	Examples
y	Year	√
Y	Week year	当天所在的周属于的年份，一周从周日开始，只要本周跨年，那么这周就算入下一年
M	Month in year	√
D	Day in year
d	Day in month	√
H	Hour in day (0-23)	√
h	Hour in am/pm (1-12)
m	Minute in hour	√
s	Second in minute	√
S	Millisecond
e.g.	yyyy-MM-dd HH:mm:ss	格式参考 java.text.SimpleDateFormat 的注释说明

3.1 使用示例

public class SimpleDateFormat extends DateFormat{
  public SimpleDateFormat(String pattern) {
     this(pattern, Locale.getDefault(Locale.Category.FORMAT));
  }
  public SimpleDateFormat(String pattern, Locale locale) {
  }
}

格式化：日期 -> 文本
解析：文本 -> 日期

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String time = sdf.format(new Date());
System.out.println(Timestamp.valueOf(time + " 00:00:00"));
System.out.println(Timestamp.valueOf(time + " 23:59:59"));

SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy/MM/dd");
// 2022/01/01 要与 yyyy/MM/dd 格式保持一致
Date date = simpleDateFormat.parse("2022/01/01");
System.out.println(date.toString());

时间戳就是一个 int 类型的数值，并不是什么timestamp字段，
字段是 timestamp 存的就是时间格式的值，你要存成 1504064065 就用 int

Timestamp ts = new Timestamp(System.currentTimeMillis());
// ts = Timestamp.valueOf(time);
System.out.println(ts);
System.out.println(Timestamp.valueOf(time));
System.out.println( new Timestamp(System.currentTimeMillis()));

3.2 线程不安全

public void demo() throws Exception {
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
    ExecutorService executorService = Executors.newFixedThreadPool(10);

    Callable caller = new Caller(simpleDateFormat);
    List<Future<Date>> list = new ArrayList<>();
    for (int i = 0; i < 10; i++) {
        Future<Date> future = executorService.submit(caller);
        list.add(future);
    }
    for (Future<Date> future : list) {
        System.out.println(future.get());
    }

    executorService.shutdown();
}

class Caller implements Callable<Date> {
    private SimpleDateFormat simpleDateFormat;
    public Caller(SimpleDateFormat simpleDateFormat) {
        this.simpleDateFormat = simpleDateFormat;
    }
    @Override
    public Date call() throws Exception {
        // 线程不安全
        return simpleDateFormat.parse("2022-01-01");
    }
}

改进：

@Override
public Date call() throws Exception {
    // 加锁
    synchronized (simpleDateFormat) {
        return simpleDateFormat.parse("2022-01-01");
    }
}

3.3 使用线程安全的DateTimeFormatter

public void demo() throws Exception {
    DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    ExecutorService executorService = Executors.newFixedThreadPool(10);

    Callable caller = new Caller(dateTimeFormatter);
    List<Future<LocalDate>> list = new ArrayList<>();
    for (int i = 0; i < 10; i++) {
        Future<LocalDate> future = executorService.submit(caller);
        list.add(future);
    }
    for (Future<LocalDate> future : list) {
        System.out.println(future.get());
    }

    executorService.shutdown();
}

class Caller implements Callable<LocalDate> {
    private DateTimeFormatter dateTimeFormatter;
    public Caller(DateTimeFormatter dateTimeFormatter) {
        this.dateTimeFormatter = dateTimeFormatter;
    }
    @Override
    public LocalDate call() throws Exception {
        return LocalDate.parse("2022-01-01", dateTimeFormatter);
    }
}

3.4 线程不安全的原因

public class SimpleDateFormat extends DateFormat{
  public SimpleDateFormat(String pattern) {
     this(pattern, Locale.getDefault(Locale.Category.FORMAT));
  }
  // java.text.DateFormat#format(java.util.Date)
  public final String format(Date date) {}
  // java.text.DateFormat#parse(java.lang.String)
  public Date parse(String source) throws ParseException {}
}

public final class LocalDate
        implements Temporal, TemporalAdjuster, ChronoLocalDate, Serializable {}

Reference

网友评论

本文标题：Java日期处理

本文链接：https://www.haomeiwen.com/subject/xjwmvrtx.html

延伸阅读

深度阅读

您也可以注册成为美文阅读网的作者，发表您的原创作品、分享您的心情！