SimpleDateFormat 转为线程安全

多线程调用是会报错。

解决方案：

/**

  * 将字符串转换为日期(与时间)

  */

 public static Date parseDatetime(String datetime) throws BusinessException {

  try {

   if (datetime.indexOf(' ') > 0) {

       return getSdf("yyyy-MM-dd HH:mm:ss").parse(datetime);

   } else {

    return getSdf("yyyy-MM-dd").parse(datetime);

   }

  } catch (Exception e) {

      e.printStackTrace();

   throw new BusinessException(ResultMsg.BEAN_COPY_EXCEPTION, "日期字符串格式错误：" + datetime);

  }

 }

/**

     * 返回一个ThreadLocal的sdf,每个线程只会new一次sdf

     */

    public static SimpleDateFormat getSdf(final String pattern) {

        ThreadLocal<SimpleDateFormat> tl = sdfMap.get(pattern);

        if (tl == null) {

            synchronized (lockObj) {

                tl = sdfMap.get(pattern);

                if (tl == null) {

                    tl = new ThreadLocal<SimpleDateFormat>() {

                     @Override

                        protected SimpleDateFormat initialValue() {

                            return new SimpleDateFormat(pattern);

                        }

                    };

                    sdfMap.put(pattern, tl);

                }

            }

        }

        return tl.get();

    }

 /** 锁对象 */

    private static final Object lockObj = new Object();

    /** 存放不同的日期模板格式的sdf的Map */

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