Java 日期比較與計算工具類：比大小、差天數、差小時、重疊區間

Java 日期比較與計算工具類：比大小、差天數、差小時、重疊區間

整理常用日期操作靜態方法，基於 SimpleDateFormat、Calendar（JDK 7 風格），JDK 8+ 建議改用 java.time 套件。

工具類完整程式碼

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;

public class DateUtils {

    private static final String DATETIME_PATTERN = "yyyy-MM-dd HH:mm:ss";
    private static final String DATE_PATTERN = "yyyy-MM-dd";
    private static final String HOUR_PATTERN = "yyyy-MM-dd HH";

    /** 1. 比較兩個日期字串大小
     * @return 1: date1 > date2, -1: date1 < date2, 0: 相等 */
    public static int compareDate(String date1, String date2) {
        DateFormat df = new SimpleDateFormat(DATETIME_PATTERN);
        try {
            Date d1 = df.parse(date1);
            Date d2 = df.parse(date2);
            long diff = d1.getTime() - d2.getTime();
            return Long.compare(diff, 0);
        } catch (ParseException e) {
            throw new IllegalArgumentException("日期格式錯誤", e);
        }
    }

    /** 2. 計算兩個日期相差天數 (忽略時分秒) */
    public static int daysBetween(String startDate, String endDate) {
        SimpleDateFormat sdf = new SimpleDateFormat(DATE_PATTERN);
        Calendar cal = Calendar.getInstance();
        try {
            cal.setTime(sdf.parse(startDate));
            long t1 = cal.getTimeInMillis();
            cal.setTime(sdf.parse(endDate));
            long t2 = cal.getTimeInMillis();
            return (int) ((t2 - t1) / (1000 * 3600 * 24));
        } catch (ParseException e) {
            throw new IllegalArgumentException("日期格式錯誤", e);
        }
    }

    /** 3. 計算兩個日期時間相差小時數 */
    public static int hoursBetween(String startTime, String endTime) {
        SimpleDateFormat sdf = new SimpleDateFormat(HOUR_PATTERN);
        Calendar cal = Calendar.getInstance();
        try {
            cal.setTime(sdf.parse(startTime));
            long t1 = cal.getTimeInMillis();
            cal.setTime(sdf.parse(endTime));
            long t2 = cal.getTimeInMillis();
            return (int) ((t2 - t1) / (1000 * 3600));
        } catch (ParseException e) {
            throw new IllegalArgumentException("日期格式錯誤", e);
        }
    }

    /** 4. 計算兩個日期區間的重疊部分
     * @return Map 包含 startDate、endDate (重疊區間)，無重疊返回空字串 */
    public static Map<String, String> overlap(String s1, String e1, String s2, String e2) {
        SimpleDateFormat sdf = new SimpleDateFormat(DATE_PATTERN);
        Map<String, String> result = new HashMap<>();
        result.put("startDate", "");
        result.put("endDate", "");
        try {
            Date d1 = sdf.parse(s1);
            Date d2 = sdf.parse(e1);
            Date d3 = sdf.parse(s2);
            Date d4 = sdf.parse(e4);

            long maxStart = Math.max(d1.getTime(), d3.getTime());
            long minEnd = Math.min(d2.getTime(), d4.getTime());

            if (maxStart <= minEnd) {
                Calendar c = Calendar.getInstance();
                c.setTimeInMillis(maxStart);
                result.put("startDate", sdf.format(c.getTime()));
                c.setTimeInMillis(minEnd);
                result.put("endDate", sdf.format(c.getTime()));
            }
        } catch (ParseException ex) {
            throw new IllegalArgumentException("日期格式錯誤", ex);
        }
        return result;
    }
}

使用範例

public static void main(String[] args) {
    System.out.println(DateUtils.compareDate("2023-01-01 10:00:00", "2023-01-01 09:00:00")); // 1
    System.out.println(DateUtils.daysBetween("2023-01-01", "2023-01-10")); // 9
    System.out.println(DateUtils.hoursBetween("2023-01-01 10", "2023-01-01 15")); // 5

    Map<String, String> ov = DateUtils.overlap("2023-01-01", "2023-01-10", "2023-01-05", "2023-01-15");
    System.out.println("重疊: " + ov.get("startDate") + " ~ " + ov.get("endDate")); // 2023-01-05 ~ 2023-01-10
}

遷移建議：JDK 8+ 使用 java.time

// 比較
LocalDateTime d1 = LocalDateTime.parse("2023-01-01T10:00:00");
LocalDateTime d2 = LocalDateTime.parse("2023-01-01T09:00:00");
int cmp = d1.compareTo(d2);

// 差天數
long days = ChronoUnit.DAYS.between(LocalDate.parse("2023-01-01"), LocalDate.parse("2023-01-10"));

// 差小時
long hours = ChronoUnit.HOURS.between(
    LocalDateTime.parse("2023-01-01T10:00"), LocalDateTime.parse("2023-01-01T15:00"));

// 區間重疊
LocalDate maxStart = LocalDate.parse("2023-01-01").isAfter(LocalDate.parse("2023-01-05")) ?
    LocalDate.parse("2023-01-01") : LocalDate.parse("2023-01-05");
// ... 類似邏輯

java.time 不可變、執行緒安全、API 豐富，新專案優先採用。