java实现日历打印

小灰灰 2022-12-30 10:51 121阅读 0赞

### 目录 ###

*  前言
 *  实现思路
 *   *  代码
     *  MonthUtils.java
     *  TimeUtils.java
     *  main方法

# 前言 #

> 最新项目需要实现月变化效果，能通过月日历查看每一天的变化情况。下面来说一说实现逻辑。

# 实现思路 #

![20201225094219583.png][]  
查看过去一年的每个月的日历，查询规律

*  日历由6行7列组成，42个单元格
 *  日历包含上个月、本月、下个月的数据。
 *  上个月的数据，先找出本月的第一周为周几，假设为周二，则上个月有一天。
 *  下个月的数据，因为固定是42个单元格，42-上个月count-本月count,则为下个月有多少天

话不多说，先看看效果  
![20201225095039338.png][]

## 代码 ##

## MonthUtils.java ##

public static  List<String> getMonthDay(String str){ 
            List<String> list = new ArrayList<>();
            String zeroStr = str+"-01 00:00:00";
    
            String firstMonthDay = TimeUtils.getFirstMonthDay(zeroStr);
            String lastMonthDay = TimeUtils.getLastMonthDay(zeroStr);
    
            int count =0;  //count计数，达到42说明月份的日历已完整
    
            //第一周为星期几
            int firstMonthDayByWeek = TimeUtils.getFirstMonthDayByWeek(zeroStr);
            //当月第一天
            Date startTime = TimeUtils.convertDate(firstMonthDay, "yyyy-MM-dd");
            Date endTime = TimeUtils.convertDate(lastMonthDay, "yyyy-MM-dd");
            for (int i = firstMonthDayByWeek - 1; i > 0; i--) { 
                String yyyyMMdd =TimeUtils.converStringDate(TimeUtils.getAfterDay(startTime, i),"yyyy-MM-dd");
                list.add(yyyyMMdd);
                count++;
            }
    
            //打印本月数据
            List<String> dateList = TimeUtils.getAscDateList(firstMonthDay, lastMonthDay,"yyyy-MM-dd");
            for (String s : dateList) { 
                list.add(s);
                count++;
            }
    
            int endDay = 42 - count;
            for (int i = 1; i <= endDay; i++) { 
                String yyyyMMdd =TimeUtils.converStringDate(TimeUtils.getAfterDay(endTime, -i),"yyyy-MM-dd");
                list.add(yyyyMMdd);
                count++;
            }
            return  list;
        }

## TimeUtils.java ##

/** * 获取当月的第一天 * @return */
    	public static final String getFirstMonthDay(String dateTime){ 
    		LocalDate localDate = getLocalDate(dateTime);
    		LocalDate with = localDate.with(TemporalAdjusters.firstDayOfMonth());
    		String firstDay = with+" 00:00:00";
    		return firstDay;
    	}
    	private static LocalDate getLocalDate(String dateTime) { 
    		DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
    		//2.把字符串转成localDate
    		return LocalDateTime.parse(dateTime, df).toLocalDate();
    	}	
    	/** * 获取当月的最后一天 * @return */
    	public static final String getLastMonthDay(String dateTime){ 
    		LocalDate localDate = getLocalDate(dateTime);
    		LocalDate with = localDate.with(TemporalAdjusters.lastDayOfMonth());
    		String firstDay = with+" 00:00:00";
    		return firstDay;
    	}
    	
    	/** * 获取当月的第一天(周几) * @return */
    	public static final int getFirstMonthDayByWeek(String dateTime){ 
    		LocalDate localDate = getLocalDate(dateTime);
    		LocalDate with = localDate.with(TemporalAdjusters.firstDayOfMonth());
    		DayOfWeek dayOfWeek = with.getDayOfWeek();
    		return  dayOfWeek.getValue();
    	}
    
    public static String converStringDate(Date date, String format) { 
    		SimpleDateFormat sdf = new SimpleDateFormat(format);
    		try { 
    			return sdf.format(date);
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}
    		return null;
    	}
    
    /** * 从小到大(取一个月的数据) * @ param formate 日期格式 */
    	public static List<String> getAscDateList(String startTime, String endTime,String formate) { 
    		LocalDate startDate = getLocalDate(startTime);
    		LocalDate endDate = getLocalDate(endTime);
    
    		List<String> result = new ArrayList<>();
    		LocalDate tempDate = null;//用户存储中间变量
    		Long num = endDate.toEpochDay() - startDate.toEpochDay();
    		for (int i = 0; i <= num; i++) { 
    			tempDate = startDate;
    			if (tempDate.toEpochDay() - endDate.toEpochDay() <= 0) { 
    				Date yyyyMMdd = TimeUtils.convertDate(startDate.toString(), "yyyy-MM-dd");
    				//14点整，取一张图片
    				result.add(TimeUtils.converStringDate(yyyyMMdd,formate));
    				startDate = tempDate.plusDays(1);
    			}
    		}
    		//System.out.println(result);
    		return result;
    	}
    
    /** * date和format格式必须一直 * * @param data * @param format * @return */
    	public static Date convertDate(String data, String format) { 
    		SimpleDateFormat sdf = new SimpleDateFormat(format);
    		Date langDate;
    		try { 
    			langDate = sdf.parse(data);
    			return langDate;
    		} catch (Exception e) { 
    			e.printStackTrace();
    		}
    		return null;
    	}
    
      /** * 获取几天之前的数据 * * @param endDate * @param day * @return */
    	public static Date getAfterDay(Date endDate, int day) { 
    		Calendar calc = Calendar.getInstance();
    		calc.setTime(endDate);
    		calc.add(calc.DATE, -day);
    		Date minDate = calc.getTime();
    		return minDate;
    	}

## main方法 ##

String str = "2020-12";
            List<String> monthDay = getMonthDay(str);
            System.out.println("星期一\t\t\t星期二\t\t\t星期三\t\t\t星期四\t\t\t星期五\t\t\t星期六\t\t\t星期日");
            int count = 1;
            for (String s : monthDay) { 
                if(count % 7 == 0){ 
                    System.out.println(s);
                }else{ 
                    System.out.print(s+"\t\t");
                }
                count++;
            }

![20201225095615331.png][]

[20201225094219583.png]: /images/20221120/7e230211ede74259a654ed4b6f56260b.png
[20201225095039338.png]: https://img-blog.csdnimg.cn/20201225095039338.png
[20201225095615331.png]: https://img-blog.csdnimg.cn/20201225095615331.png