Java获取当前时间详解

/** 
     * 获取当前时间 
     *  
     * @param args 
     */ 
    public static String getNowTime() { 
        Calendar cal = Calendar.getInstance(); 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        String lastMonth = dft.format(cal.getTime()); 
        return lastMonth; 
    } 
 
    /** 
     * 判断当天是否为本月第一天 
     *  
     * @return 
     */ 
    public static boolean isFirstDayOfMonth() { 
        boolean flag = false; 
        Calendar calendar = Calendar.getInstance(); 
        int today = calendar.get(calendar.DAY_OF_MONTH); 
        if (1 == today) { 
            flag = true; 
        } 
        return flag; 
    } 
 
    /** 
     * 获取当前月份最后一天 
     *  
     * @param date 
     * @return 
     * @throws ParseException 
     */ 
    public static String getMaxMonthDate() { 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        Calendar calendar = Calendar.getInstance(); 
        calendar.setTime(new Date()); 
        // calendar.add(Calendar.MONTH, -1); 
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); 
        return dft.format(calendar.getTime()); 
    } 
 
    /** 
     *  
     * 描述:获取下一个月的第一天. 
     *  
     * @return 
     */ 
    public static String getPerFirstDayOfMonth() { 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        Calendar calendar = Calendar.getInstance(); 
        calendar.add(Calendar.MONTH, 1); 
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMinimum(Calendar.DAY_OF_MONTH)); 
        return dft.format(calendar.getTime()); 
    } 
 
    /** 
     *  
     * 描述:获取上个月的最后一天. 
     *  
     * @return 
     */ 
    public static String getLastMaxMonthDate() { 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        Calendar calendar = Calendar.getInstance(); 
        calendar.setTime(new Date()); 
        calendar.add(Calendar.MONTH, -1); 
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); 
        return dft.format(calendar.getTime()); 
    } 
 
    /** 
     * 获取上一个月 
     *  
     * @return 
     */ 
    public static String getLastMonth() { 
        Calendar cal = Calendar.getInstance(); 
        cal.add(cal.MONTH, -1); 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMM"); 
        String lastMonth = dft.format(cal.getTime()); 
        return lastMonth; 
    } 
 
    /** 
     *  
     * 描述:获取下一个月. 
     *  
     * @return 
     */ 
    public static String getPreMonth() { 
        Calendar cal = Calendar.getInstance(); 
        cal.add(cal.MONTH, 1); 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMM"); 
        String preMonth = dft.format(cal.getTime()); 
        return preMonth; 
    } 
 
// 是否是最后一天 
    public static boolean isLastDayOfMonth() { 
        boolean flag = false; 
        if (StringUtils.isNotBlank(getNowTime()) && StringUtils.isNotBlank(getMaxMonthDate()) && StringUtils.equals(getNowTime(), getMaxMonthDate())) { // getMaxMonthDate().equals(getNowTime()) 
            flag = true; 
        } 
        return flag; 
    } 
     
    /** 
     * 获取任意时间的下一个月 
     * 描述:<描述函数实现的功能>. 
     * @param repeatDate 
     * @return 
     */ 
    public static String getPreMonth(String repeatDate) { 
        String lastMonth = ""; 
        Calendar cal = Calendar.getInstance(); 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMM"); 
        int year = Integer.parseInt(repeatDate.substring(0, 4)); 
        String monthsString = repeatDate.substring(4, 6); 
        int month; 
        if ("0".equals(monthsString.substring(0, 1))) { 
            month = Integer.parseInt(monthsString.substring(1, 2)); 
        } else { 
            month = Integer.parseInt(monthsString.substring(0, 2)); 
        } 
        cal.set(year,month,Calendar.DATE); 
        lastMonth = dft.format(cal.getTime()); 
        return lastMonth; 
    } 
     
    /** 
     * 获取任意时间的上一个月 
     * 描述:<描述函数实现的功能>. 
     * @param repeatDate 
     * @return 
     */ 
    public static String getLastMonth(String repeatDate) { 
        String lastMonth = ""; 
        Calendar cal = Calendar.getInstance(); 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMM"); 
        int year = Integer.parseInt(repeatDate.substring(0, 4)); 
        String monthsString = repeatDate.substring(4, 6); 
        int month; 
        if ("0".equals(monthsString.substring(0, 1))) { 
            month = Integer.parseInt(monthsString.substring(1, 2)); 
        } else { 
            month = Integer.parseInt(monthsString.substring(0, 2)); 
        } 
        cal.set(year,month-2,Calendar.DATE); 
        lastMonth = dft.format(cal.getTime()); 
        return lastMonth; 
    } 
     // 
    /** 
     * 获取任意时间的月的最后一天 
     * 描述:<描述函数实现的功能>. 
     * @param repeatDate 
     * @return 
     */ 
    private static String getMaxMonthDate(String repeatDate) { 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        Calendar calendar = Calendar.getInstance(); 
        try { 
            if(StringUtils.isNotBlank(repeatDate) && !"null".equals(repeatDate)){ 
                calendar.setTime(dft.parse(repeatDate)); 
            } 
        } catch (ParseException e) { 
            e.printStackTrace(); 
        } 
        // calendar.add(Calendar.MONTH, -1); 
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH)); 
        return dft.format(calendar.getTime()); 
    } 
     
    /** 
     * 获取任意时间的月第一天 
     * 描述:<描述函数实现的功能>. 
     * @param repeatDate 
     * @return 
     */ 
    private static String getMinMonthDate(String repeatDate){ 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        Calendar calendar = Calendar.getInstance(); 
        try { 
            if(StringUtils.isNotBlank(repeatDate) && !"null".equals(repeatDate)){ 
                calendar.setTime(dft.parse(repeatDate)); 
            } 
        } catch (ParseException e) { 
            e.printStackTrace(); 
        } 
        // calendar.add(Calendar.MONTH, -1); 
        calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMinimum(Calendar.DAY_OF_MONTH)); 
       return dft.format(calendar.getTime());         
    } 
/** 
     * 不论是当前时间，还是历史时间  皆是时间点的前天 
     * repeatDate  任意时间 
     */ 
    public static String getModify2DaysAgo(String repeatDate) { 
        Calendar cal = Calendar.getInstance(); 
        String daysAgo = ""; 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        if (repeatDate == null || "".equals(repeatDate)) { 
            cal.set(Calendar.DATE, cal.get(Calendar.DATE) - 2); 
 
        } else { 
            int year = Integer.parseInt(repeatDate.substring(0, 4)); 
            String monthsString = repeatDate.substring(4, 6); 
            int month; 
            if ("0".equals(monthsString.substring(0, 1))) { 
                month = Integer.parseInt(monthsString.substring(1, 2)); 
            } else { 
                month = Integer.parseInt(monthsString.substring(0, 2)); 
            } 
            String dateString = repeatDate.substring(6, 8); 
            int date; 
            if ("0".equals(dateString.subSequence(0, 1))) { 
                date = Integer.parseInt(dateString.substring(1, 2)); 
            } else { 
                date = Integer.parseInt(dateString.substring(0, 2)); 
            } 
            cal.set(year, month-1, date - 1); 
            System.out.println(dft.format(cal.getTime())); 
        } 
        daysAgo = dft.format(cal.getTime()); 
        return daysAgo; 
    } 
     
    /** 
     * 不论是当前时间，还是历史时间  皆是时间点的T-N天 
    * repeatDate 任意时间    param 数字 可以表示前几天 
     */ 
    public static String getModifyNumDaysAgo(String repeatDate,int param) { 
        Calendar cal = Calendar.getInstance(); 
        String daysAgo = ""; 
        SimpleDateFormat dft = new SimpleDateFormat("yyyyMMdd"); 
        if (repeatDate == null || "".equals(repeatDate)) { 
            cal.set(Calendar.DATE, cal.get(Calendar.DATE) - param); 
 
        } else { 
            int year = Integer.parseInt(repeatDate.substring(0, 4)); 
            String monthsString = repeatDate.substring(4, 6); 
            int month; 
            if ("0".equals(monthsString.substring(0, 1))) { 
                month = Integer.parseInt(monthsString.substring(1, 2)); 
            } else { 
                month = Integer.parseInt(monthsString.substring(0, 2)); 
            } 
            String dateString = repeatDate.substring(6, 8); 
            int date; 
            if ("0".equals(dateString.subSequence(0, 1))) { 
                date = Integer.parseInt(dateString.substring(1, 2)); 
            } else { 
                date = Integer.parseInt(dateString.substring(0, 2)); 
            } 
            cal.set(year, month-1, date - param+1); 
            System.out.println(dft.format(cal.getTime())); 
        } 
        daysAgo = dft.format(cal.getTime()); 
        return daysAgo; 
    }