JAVA日期時間如何比較

    Timestamp crsd = verifyItem.getRequestshipdate();
                Calendar cal = Calendar.getInstance();
                Calendar now = Calendar.getInstance();
                Calendar calCrsd = Calendar.getInstance();
                calCrsd.setTimeInMillis(crsd.getTime());
                cal.set(calCrsd.get(Calendar.YEAR),
                        calCrsd.get(Calendar.MONTH),
                        calCrsd.get(Calendar.DATE), 0, 0, 0);
                cal.add(Calendar.DATE, -leadtime);// 如果允許提前3天發貨，而客戶請求8日發貨，則最早可以允許5日發貨。
                now.set(now.get(Calendar.YEAR), now.get(Calendar.MONTH), now.get(Calendar.DATE), 0, 0, 0);

                if (now.compareTo(cal) < 0) {
                    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
                    infos.add("訂單[單號：" + so + "，行號：" + soline
                            + "]未排入計劃！原因：要排入計劃的訂單只允許提前" + leadtime
                            + "天發貨[客戶請求發貨日期為" + df.format(calCrsd.getTime())
                            + "，允許發貨的最早日期為" + df.format(cal.getTime()) + "]！");
                    fails.add(verifyItem.getId());
                    removeIds.add(verifyItem);
                    continue;
                }