Java 如何确定日期正则表达式？

我试图将正则表达式仅用于dd/MM/yyyy日期格式，但如果输入dd/MM/yy值，它会接受。我想知道如何使其仅接受dd/MM/yyyy值

如果我使用

new SimpleDateFormat("dd/MM/yyyy").parse(value); 

代码继续接受dd/MM/yy格式

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我建议您从过时且容易出错的java.util日期时间API和SimpleDataFormat切换到java.time日期时间API和相应的格式化API包java.time.format。从了解有关现代日期时间API的更多信息

示例运行：

正则表达式解决方案：

示例运行：

正则表达式的解释：

\d指定一个数字 X{n}X，正好n次

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请在这里用英语提问或继续提问。顺便问一下，为什么要用正则表达式重新格式化日期字符串？您可以使用java.time.LocalDate和合适的java.time.format.DateTimeFormatters。我尝试使用但仍然接受值dd/mm/yyyyyy您需要一个DateTimeFormatter.ofPatterndd/mm/uu.WithResolversTyle.STRICT；，只接受两位数的年份。DateTimeFormatter with Resolverstyle=DateTimeFormatter.of模式dd/MM/yyyy。withResolverStyle Resolverstyle.STRICT；LocalDate.parsevalue，带ResolverStyle@德哈尔，谢谢你

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
    
public class Main {
    public static void main(String[] args) {
        String value = "10/02/20";
                    
        Pattern pattern = Pattern.compile("^([0-2][0-9]||3[0-1])/(0[0-9]||1[0-2])/([0-9][0-9])?[0-9][0-9]$");
                        
        Matcher matcher = pattern.matcher(value);
            
        System.out.println(matcher.find());
    }
}

import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeParseException;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Define the format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");

        String dateString;
        LocalDate date = null;
        boolean valid;

        do {
            valid = true;
            System.out.print("Enter a date in dd/MM/yyyy format: ");
            dateString = scanner.nextLine();
            try {
                // Try to parse the input string
                date = LocalDate.parse(dateString, formatter);
            } catch (DateTimeParseException e) {
                System.out.println("Invalid format");
                // Set `valid` to false in case of exception
                valid = false;
            }
        } while (!valid);// Loop as long as valid is false

        System.out.println("Date in ISO-8601 format: " + date);
        System.out.println("Date in dd/MM/yyyy format: " + date.format(formatter));
    }
}

Enter a date in dd/MM/yyyy format: 09/09/20
Invalid format
Enter a date in dd/MM/yyyy format: 09/09/2020
Date in ISO-8601 format: 2020-09-09
Date in dd/MM/yyyy format: 09/09/2020

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String dateString;
        boolean valid;
        do {
            valid = true;
            System.out.print("Enter a date in dd/MM/yyyy format: ");
            dateString = scanner.nextLine();
            if (!dateString.matches("\\d{2}\\/\\d{2}\\/\\d{4}")) {
                System.out.println("Invalid format");
                valid = false;
            }
        } while (!valid);// Loop as long as valid is false
        System.out.println(dateString);
    }
}

Enter a date in dd/MM/yyyy format: 09/09/20
Invalid format
Enter a date in dd/MM/yyyy format: 09/09/2020
09/09/2020