JAVA中的SimpleDateFormat是非线程安全的，所有在1.8的JDK版本里提供了线程安全的DateTimeFormatter类，由于是线程安全的，故我们可以将此类缓存起来多次利用提高效率。
同时在JDK8中提供了LocalDate、LocalTime、LocalDateTime，下面的工具类也对这3个新类提供了格式化和反格式化的支持。
package com.longge.util; import java.time.Instant; import java.time.LocalDate; import java.time.LocalDateTime; import java.time.Period; import java.time.ZoneId; import java.time.format.DateTimeFormatter; import java.util.Calendar; import java.util.Date; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.TimeUnit; import org.apache.commons.lang3.StringUtils; import com.longge.exception.TimeUnitNotSupportException; import lombok.NonNull; /** * 带缓存的基于DateTimeFormatter的日期格式化工具类 * @author yangzhilong * @date 6/21/2019 */ public class DateUtils { private static final Map<String, DateTimeFormatter> FORMATTER_CACHE = new ConcurrentHashMap<>(); private DateUtils() {} /** * 日期的格式化定义 * @author yangzhilong * @date 6/21/2019 */ public static class Pattern { private Pattern() {} public static class Date { private Date() {} /** * yyyy-MM-dd */ public static final String YYYY_MM_DD = "yyyy-MM-dd"; /** * yyyy-M-dd */ public static final String YYYY_M_DD = "yyyy-M-dd"; /** * yyyy-M-d */ public static final String YYYY_M_D = "yyyy-M-d"; /** * yyyy/MM/dd */ public static final String YYYY_MM_DD_2 = "yyyy/MM/dd"; /** * yyyy/M/dd */ public static final String YYYY_M_DD_2 = "yyyy/M/dd"; /** * yyyy/M/d */ public static final String YYYY_M_D_2 = "yyyy/M/d"; /** * yyyyMMdd */ public static final String YYYYMMDD = "yyyyMMdd"; /** * yyyyMdd */ public static final String YYYYMDD = "yyyyMdd"; /** * yyyyMd */ public static final String YYYYMD = "yyyyMd"; /** * MM-dd-yyyy */ public static final String MM_DD_YYYY = "MM-dd-yyyy"; /** * M-dd-yyyy */ public static final String M_DD_YYYY = "M-dd-yyyy"; /** * M-d-yyyy */ public static final String M_D_YYYY = "M-d-yyyy"; /** * MM/dd/yyyy */ public static final String MM_DD_YYYY_2 = "MM/dd/yyyy"; /** * M/dd/yyyy */ public static final String M_DD_YYYY_2 = "M/dd/yyyy"; /** * M/d/yyyy */ public static final String M_D_YYYY_2 = "M/d/yyyy"; /** * MMddyyyy */ public static final String MMDDYYYY = "MMddyyyy"; /** * Mddyyyy */ public static final String MDDYYYY = "Mddyyyy"; /** * Mdyyyy */ public static final String MDYYYY = "Mdyyyy"; } public static class DateTime { private DateTime() {} /** * yyyy-MM-dd HH:mm:ss */ public static final String YYYY_MM_DD_SPACE_HH_MM_SS = "yyyy-MM-dd HH:mm:ss"; /** * yyyy-M-d H:m:s */ public static final String YYYY_M_D_SPACE_H_M_S = "yyyy-M-d H:m:s"; /** * yyyy/MM/dd HH:mm:ss */ public static final String YYYY_MM_DD_SPACE_HH_MM_SS2 = "yyyy/MM/dd HH:mm:ss"; /** * HH:mm yyyy-MM-dd */ public static final String HH_MM_SPACE_YYYY_MM_DD = "HH:mm yyyy-MM-dd"; /** * HH:mm yyyy/MM/dd */ public static final String HH_MM_SPACE_YYYY_MM_DD2 = "HH:mm yyyy/MM/dd"; /** * H:mm yyyy-MM-dd */ public static final String H_MM_SPACE_YYYY_MM_DD = "H:mm yyyy-MM-dd"; /** /** * H:mm yyyy/MM/dd */ public static final String H_MM_SPACE_YYYY_MM_DD2 = "H:mm yyyy/MM/dd"; /** * H:mm,yyyy-MM-dd */ public static final String H_MM_COMMA_YYYY_MM_DD = "H:mm,yyyy-MM-dd"; /** * H:mm,yyyy-MM-dd */ public static final String H_MM_COMMA_YYYY_MM_DD2 = "H:mm,yyyy/MM/dd"; /** * H:mm,yyyy-M-d */ public static final String H_MM_COMMA_YYYY_M_D = "H:mm,yyyy-M-d"; /** * H:m,yyyy-M-d */ public static final String H_M_COMMA_YYYY_M_D = "H:m,yyyy-M-d"; /** * H:mm,yyyy-M-d */ public static final String H_MM_COMMA_YYYY_M_D2 = "H:mm,yyyy/M/d"; /** * H:m,yyyy-M-d */ public static final String H_M_COMMA_YYYY_M_D2 = "H:m,yyyy/M/d"; } } /** * 格式化不带时分秒的日期 * @param date * @param pattern {@link DateUtils.Pattern.Date} * @return */ public static String formatDate(@NonNull Date date, @NonNull String pattern) { Instant instant = date.toInstant(); ZoneId zone = ZoneId.systemDefault(); LocalDate localDate = LocalDateTime.ofInstant(instant, zone).toLocalDate(); return formatDate(localDate, pattern); } /** * 格式化不带时分秒的LocalDate * @param localDate * @param pattern {@link DateUtils.Pattern.Date} * @return */ public static String formatDate(@NonNull LocalDate localDate, @NonNull String pattern) { if(StringUtils.isBlank(pattern)) { throw new NullPointerException("pattern is null"); } DateTimeFormatter formatter = createCacheFormatter(pattern); return localDate.format(formatter); } /** * 格式化带时分秒的日期 * @param date * @param pattern {@link DateUtils.Pattern.DateTime} * @return */ public static String formatDateTime(@NonNull Date date, @NonNull String pattern) { LocalDateTime formatDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault()); return formatDateTime(formatDateTime, pattern); } /** * 格式化带时分秒的LocalDateTime * @param localDateTime * @param pattern {@link DateUtils.Pattern.DateTime} * @return */ public static String formatDateTime(@NonNull LocalDateTime localDateTime, @NonNull String pattern) { if(StringUtils.isBlank(pattern)) { throw new NullPointerException("pattern is null"); } DateTimeFormatter formatter = createCacheFormatter(pattern); return localDateTime.format(formatter); } /** * 转换不带时分秒的字符串到Date * @param date * @param pattern {@link DateUtils.Pattern.Date} * @return */ public static Date parseDate(@NonNull String date, @NonNull String pattern) { LocalDate localDate = parseLocalDate(date, pattern); Instant instant = localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant(); return Date.from(instant); } /** * 转换不带时分秒的字符串到LocalDate * @param date * @param pattern {@link DateUtils.Pattern.Date} * @return */ public static LocalDate parseLocalDate(@NonNull String date, @NonNull String pattern) { if(StringUtils.isBlank(date)) { throw new NullPointerException("date is null"); } if(StringUtils.isBlank(pattern)) { throw new NullPointerException("pattern is null"); } DateTimeFormatter formatter = createCacheFormatter(pattern); return LocalDate.parse(date, formatter); } /** * 转换带时分秒的字符串到Date * @param dateTime * @param pattern {@link DateUtils.Pattern.Date} * @return */ public static Date parseDateTime(@NonNull String dateTime, @NonNull String pattern) { if(StringUtils.isBlank(dateTime)) { throw new NullPointerException("date is null"); } if(StringUtils.isBlank(pattern)) { throw new NullPointerException("pattern is null"); } LocalDateTime localDateTime = parseLocalDateTime(dateTime, pattern); Instant instant = localDateTime.atZone(ZoneId.systemDefault()).toInstant(); return Date.from(instant); } /** * 转换带时分秒的字符串到LocalDateTime * @param dateTime * @param pattern {@link DateUtils.Pattern.DateTime} * @return */ public static LocalDateTime parseLocalDateTime(@NonNull String dateTime, @NonNull String pattern) { DateTimeFormatter formatter = createCacheFormatter(pattern); return LocalDateTime.parse(dateTime, formatter); } /** * 日期的加减(仅支持天/小时/分/秒) * @param date * @param addValue * @param unit * @return */ public static Date dateAdd(@NonNull Date date, int addValue, TimeUnit unit) { Calendar cal = Calendar.getInstance(); cal.setTime(date); if (TimeUnit.DAYS.equals(unit)) { cal.add(Calendar.DAY_OF_YEAR, addValue); } else if (TimeUnit.HOURS.equals(unit)) { cal.add(Calendar.HOUR_OF_DAY, addValue); } else if (TimeUnit.MINUTES.equals(unit)) { cal.add(Calendar.MINUTE, addValue); } else if (TimeUnit.SECONDS.equals(unit)) { cal.add(Calendar.SECOND, addValue); } else { throw new TimeUnitNotSupportException(); } return cal.getTime(); } /** * 计算2个日期的差 * @param begin * @param end * @return */ public static Period calculationPeriod(@NonNull Date begin, Date end) { Calendar beginCal = Calendar.getInstance(); beginCal.setTime(begin); Calendar endCal = Calendar.getInstance(); endCal.setTime(end); LocalDate beginLocal = LocalDate.of(beginCal.get(Calendar.YEAR), beginCal.get(Calendar.MONTH), beginCal.get(Calendar.DAY_OF_YEAR)); LocalDate endLocal = LocalDate.of(beginCal.get(Calendar.YEAR), beginCal.get(Calendar.MONTH), beginCal.get(Calendar.DAY_OF_YEAR)); return Period.between(beginLocal, endLocal); } /** * DateTimeFormatter缓存处理 * @param begin * @param end * @return */ private static DateTimeFormatter createCacheFormatter(String pattern) { if (pattern == null || pattern.length() == 0) { throw new IllegalArgumentException("Invalid pattern specification"); } DateTimeFormatter formatter = FORMATTER_CACHE.get(pattern); if(null == formatter) { formatter = DateTimeFormatter.ofPattern(pattern); FORMATTER_CACHE.put(pattern, formatter); } return formatter; } }