日期工具类

package com.hq.alp.util;

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

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 日期工具类(使用了ThreadLocal获取SimpleDateFormat)
 * 
 * @author xianglong
 * @date 2019年5月14日 下午4:49:46
 */
public class DateUtil {

	private static Map<String, ThreadLocal<SimpleDateFormat>> sdfMap = new HashMap<String, ThreadLocal<SimpleDateFormat>>();

	private static Logger logger = LoggerFactory.getLogger(DateUtil.class);

	public final static String MDHMSS = "MMddHHmmssSSS";
	public final static String YMDHMS = "yyyyMMddHHmmss";
	public final static String YMDHMS_ = "yyyy-MM-dd HH:mm:ss";
	public final static String YMD = "yyyyMMdd";
	public final static String YMD_ = "yyyy-MM-dd";
	public final static String HMS = "HHmmss";

	/**
	 * 根据map中的key得到对应线程的sdf实例
	 * 
	 * @param pattern
	 *            map中的key
	 * @return 该实例
	 */
	private static SimpleDateFormat getSdf(final String pattern) {
		ThreadLocal<SimpleDateFormat> sdfThread = sdfMap.get(pattern);
		if (sdfThread == null) {
			// 双重检验,防止sdfMap被多次put进去值,和双重锁单例原因是一样的
			synchronized (DateUtil.class) {
				sdfThread = sdfMap.get(pattern);
				if (sdfThread == null) {
					logger.debug("put new sdf of pattern " + pattern + " to map");
					sdfThread = new ThreadLocal<SimpleDateFormat>() {
						@Override
						protected SimpleDateFormat initialValue() {
							logger.debug("thread: " + Thread.currentThread() + " init pattern: " + pattern);
							return new SimpleDateFormat(pattern);
						}
					};
					sdfMap.put(pattern, sdfThread);
				}
			}
		}
		return sdfThread.get();
	}

	/**
	 * 按照指定pattern解析日期
	 * 
	 * @param date
	 *            要解析的date
	 * @param pattern
	 *            指定格式
	 * @return 解析后date实例
	 */
	public static Date parseDate(String date, String pattern) {
		if (date == null) {
			throw new IllegalArgumentException("The date must not be null");
		}
		try {
			return getSdf(pattern).parse(date);
		} catch (ParseException e) {
			e.printStackTrace();
			logger.error("解析的格式不支持:" + pattern);
		}
		return null;
	}

	/**
	 * 按照指定pattern格式化日期
	 * 
	 * @param date
	 *            要格式化的date
	 * @param pattern
	 *            指定格式
	 * @return 解析后格式
	 */
	public static String formatDate(Date date, String pattern) {
		if (date == null) {
			throw new IllegalArgumentException("The date must not be null");
		} else {
			return getSdf(pattern).format(date);
		}
	}

	//测试
	public static void main(String[] args) {
		DateUtil.formatDate(new Date(), MDHMSS);
		new Thread(() -> {
			DateUtil.formatDate(new Date(), MDHMSS);
		}).start();
		new Thread(() -> {
			DateUtil.formatDate(new Date(), MDHMSS);
		}).start();
	}

}