java 格式转换:输入日期格式和日期字符串，返回yyyy-MM-dd格式的日期

输入日期格式和日期字符串，实现返回yyyy-MM-dd格式的日期。

YYYY，YY   ，DD，WW   自由组合。

YYYY，YY  ，MM    自由组合。

最后返回yyyy-MM-dd格式的日期

前提条件是 日期格式和日期字符串配备才可以。

比如：

日期格式："DD/MM/YYYY"  ；  日期字符串 ： "21112024" ；  返回 2024-21-11

日期格式："YYWW"  ；  日期字符串 ： "2250"

日期格式："yyMMdd"  ；  日期字符串 ： "221224"

这样的。

实现代码

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.time.temporal.TemporalAdjusters;
import java.util.Date;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

public class DateFormatConvert {

    public static LocalDate formatDatetime(String dtStr, String format, int weekRule) throws Exception {

        LocalDate date = LocalDate.now();
        try {
            // Map to store the extracted date components
            Map<String, String> dateComponents = new HashMap<>();
            String dateStr = dtStr;
            String formatStr = format.replace("/", "").toUpperCase();
            dtStr = dtStr.replace("/", "");
            int year = 0;int month = 0;int day = 0;

            // Handle special case for 'D' at the beginning
            if (dtStr.startsWith("D")) {
                //format = format.substring(1);
                dtStr = dtStr.substring(1);
            }

            if(format.equalsIgnoreCase("YYYY-MM-DD")){
                DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
                try {
                    LocalDate localDate = LocalDate.parse(dtStr, formatter);
                    System.out.println("The date string is valid: " + localDate);
                    return localDate;
                } catch (DateTimeParseException e) {
                    System.out.println("The date string is invalid: " + e.getMessage());
                    throw new Exception("Format(" + format + ") and DateCode( " + dtStr + " ) do not match ");
                }
            }
            if(formatStr.length() != dtStr.length()){
                throw new Exception("Format and DateCode do not match ");
            }
            // Extract date components based on the format
            if (formatStr.contains("YYYY")) {
                int yyyy = formatStr.indexOf("YYYY");
                dateComponents.put("year", dtStr.substring(yyyy, yyyy+4));
                year = Integer.parseInt(dtStr.substring(yyyy, yyyy+4));
            } else if (formatStr.contains("YY")) {
                int yy = formatStr.indexOf("YY");
                String yearStr = "20" + dtStr.substring(yy, yy+2);
                year = Integer.parseInt(yearStr); // Convert YY to YYYY
                dateComponents.put("year", yearStr);
            }
            if (formatStr.contains("MM")) {
                int mm = formatStr.indexOf("MM");
                month = Integer.parseInt(dtStr.substring(mm, mm+2));
                dateComponents.put("month", dtStr.substring(mm, mm+2));
            }
            if (formatStr.contains("DD")) {
                int dd = formatStr.indexOf("DD");
                day = Integer.parseInt(dtStr.substring(dd, dd+2));
                dateComponents.put("day", dtStr.substring(dd, dd+2));
            } else if (formatStr.contains("D")) {
                // Remaining 'D' case, should be handled last
                int d = formatStr.indexOf("D");
                day =  Integer.parseInt("0" + dtStr.charAt(d));
                dateComponents.put("day", String.valueOf(day)); // Only one digit day
            }

            // Handle week number (WW) if present 算法规则： 1月1日是星期一则为第一周，不是后一周为第一周。
            if (formatStr.contains("WW") && weekRule == 0) {
                int ww = formatStr.indexOf("WW");
                String week = dtStr.substring(ww, ww+2);
                dateComponents.put("week", week);
                int weekNumber = Integer.parseInt(week);
                // 验证周数是否在有效范围内
                if (weekNumber < 1 || weekNumber > 53) {
                    throw new Exception("week in 1-53 !!!");
                }
                if(year != 0){
                    date = date.withYear(year);
                }
                LocalDate firstDayOfYear = date.withDayOfYear(1);
                //从第一周的星期一开始算起。
                LocalDate dateOfWeek = firstDayOfYear.with(TemporalAdjusters.nextOrSame(java.time.DayOfWeek.MONDAY))
                        .plusWeeks(weekNumber - 1);
                // Adjust year if the calculated date falls in the next year due to week number being late in the year
                if (dateOfWeek.getYear() != date.getYear()) {
                    date = dateOfWeek.withYear(date.getYear());
                    if (date.isAfter(dateOfWeek)) {
                        date = dateOfWeek;
                        System.out.println(" 三  1 该周的开始日期是: " + date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
                    } else {
                        LocalDate correctDate = LocalDate.of(date.getYear(), 1, 1)
                                .with(TemporalAdjusters.nextOrSame(java.time.DayOfWeek.MONDAY))
                                .plusWeeks(weekNumber - 1);
                        date = correctDate;
                        System.out.println(" 三  2 该周的开始日期是: " + date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
                    }
                } else {
                    date = dateOfWeek;
                }
                System.out.println(" 三  3 该周的开始日期是: " + date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
                return LocalDate.parse(date.format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));

            }
            //算法规则： 如果第一个星期四不在第一周，我们需要回退到前一周的星期四
            if(formatStr.contains("WW") && weekRule == 1){
                int ww = formatStr.indexOf("WW");
                String week = dtStr.substring(ww, ww+2);
                dateComponents.put("week", week);
                int weekNumber = Integer.parseInt(week);
                // 验证周数是否在有效范围内
                if (weekNumber < 1 || weekNumber > 53) {
                    throw new Exception("week in 1-53 !!!");
                }
                if(year != 0){
                    date = date.withYear(year);
                }
                // 获取ISO周字段（考虑周一为一周的第一天）
                //WeekFields weekFields = WeekFields.of(Locale.getDefault()); // 1表示周一为一周的第一天
                WeekFields weekFields = WeekFields.of(DayOfWeek.MONDAY,1); // 1表示周一为一周的第一天
                // 由于我们不知道第一周的确切日期，我们需要找到该年的第一个星期四（ISO 8601标准）
                // 然后我们可以计算出第一周的起始日期
                LocalDate firstThursdayOfYear = LocalDate.of(year, 1, 1)
                        .with(ChronoField.ALIGNED_WEEK_OF_MONTH, 1) // 这通常会给我们1月的第一周，但不一定是ISO周
                        .with(TemporalAdjusters.nextOrSame(java.time.DayOfWeek.THURSDAY)); // 找到第一个星期四

                // 如果第一个星期四不在第一周，我们需要回退到前一周的星期四
                LocalDate firstWeekStart = firstThursdayOfYear;
                if (firstThursdayOfYear.get(weekFields.weekOfWeekBasedYear()) != 1) {
                    firstWeekStart = firstThursdayOfYear.minusWeeks(1).with(TemporalAdjusters.previousOrSame(java.time.DayOfWeek.THURSDAY));
                }

                // 现在我们知道第一周的起始日期，我们可以加上所需的周数来找到目标日期
                //int weekNumber = Integer.parseInt(ww);
                LocalDate targetDate = firstWeekStart.plusWeeks(weekNumber - 1); // 减1是因为我们已经有了第一周的起始日期
                // 格式化输出日期
                DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
                System.out.println(" 五 该周的开始日期是: " + targetDate.format(formatter));
                return LocalDate.parse(targetDate.format(formatter));
            }

            // Format the final date
            String formattedDate = String.format("%s-%s-%s",
                    dateComponents.getOrDefault("year", "2024"),
                    dateComponents.getOrDefault("month", "01"),
                    dateComponents.getOrDefault("day", "01"));

            // Validate the formatted date (optional, for robustness)
            DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
            LocalDate dt = LocalDate.parse(formattedDate, formatter);

            System.out.println(" TEST 该周的开始日期是: " + dt);
            return dt;
        }  catch (ParseException e) {
            throw new Exception(e.getMessage()); // Or handle the error appropriately
        }catch (Exception ex) {
            throw new Exception(ex.getMessage());
        }
    }
}