feat: 健康管理系统，代码提交。

ruoyi-common/ruoyi-common-core/src/main/java/com/ruoyi/common/core/utils/DateUtils.java

@@ -220,7 +220,26 @@ public class DateUtils extends org.apache.commons.lang3.time.DateUtils
         calendar.set(Calendar.DAY_OF_MONTH, calendar.getActualMaximum(Calendar.DAY_OF_MONTH));
         return  sdf.format(calendar.getTime());
     }
+    /**
+     * 获取选取日期的当前月的第一天
+     */
+    public static String getAgeByBirthday(Date birthday)
+    {
+       // 假设生日是2000年1月1日
+        Calendar birthdayDate = Calendar.getInstance();
+        birthdayDate.setTime(birthday);
+        Calendar currentDate = Calendar.getInstance();
 
+        // 方法三：使用Calendar类计算年龄差距
+        int ageInYears = currentDate.get(Calendar.YEAR) - birthdayDate.get(Calendar.YEAR);
+
+        if (birthdayDate.get(Calendar.MONTH) > currentDate.get(Calendar.MONTH) ||
+                (birthdayDate.get(Calendar.MONTH) == currentDate.get(Calendar.MONTH)
+                        && birthdayDate.get(Calendar.DATE) > currentDate.get(Calendar.DATE))) {
+            ageInYears--;
+        }
+       return  ageInYears + "周岁";
+    }
 
 
 }