英文:
how to fix the date regex?
问题
我试图仅使用正则表达式匹配`dd/MM/yyyy`日期格式，但如果我输入`dd/MM/yy`值，它也会被接受。我想知道如何使其只接受`dd/MM/yyyy`格式的值。
如果我使用
```Java
new SimpleDateFormat("dd/MM/yyyy").parse(value);
代码仍然会接受dd/MM/yy格式。
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]$");
Matcher matcher = pattern.matcher(value);
System.out.println(matcher.find());
}
}
<details>
<summary>英文:</summary>
I'm trying to use the regex only for the `dd/MM/yyyy` date format but if I enter the `dd/MM/yy` value it accepts. I would like to know how to make it accept only the `dd/MM/yyyy` values.
If I use
```Java
new SimpleDateFormat("dd/MM/yyyy").parse(value);
the code continues to accept dd/MM/yy format.
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static void main(String[] args) {
String value = "10/02/20";
Pattern pattern = Pattern.compile("^([0-2][0-9]||3[0-1])/(0[0-9]||1[0-2])/([0-9][0-9])?[0-9][0-9]$");
Matcher matcher = pattern.matcher(value);
System.out.println(matcher.find());
}
}
答案1
得分: 1
我建议您从过时且容易出错的 java.util 日期时间 API 和 SimpleDateFormat 切换到现代的 java.time 日期时间 API 和相应的格式化 API（包名为 java.time.format）。从 Trail: Date Time 了解更多关于现代日期时间 API 的信息。
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);
// 定义格式
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy");
String dateString;
LocalDate date = null;
boolean valid;
do {
valid = true;
System.out.print("输入格式为 dd/MM/yyyy 的日期：");
dateString = scanner.nextLine();
try {
// 尝试解析输入字符串
date = LocalDate.parse(dateString, formatter);
} catch (DateTimeParseException e) {
System.out.println("无效格式");
// 异常时将 `valid` 设置为 false
valid = false;
}
} while (!valid); // 只要 valid 为 false 就循环
System.out.println("以 ISO-8601 格式的日期：" + date);
System.out.println("以 dd/MM/yyyy 格式的日期：" + date.format(formatter));
}
}
示例运行：
输入格式为 dd/MM/yyyy 的日期：09/09/20
无效格式
输入格式为 dd/MM/yyyy 的日期：09/09/2020
以 ISO-8601 格式的日期：2020-09-09
以 dd/MM/yyyy 格式的日期：09/09/2020
正则表达式解决方案：
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("输入格式为 dd/MM/yyyy 的日期：");
dateString = scanner.nextLine();
if (!dateString.matches("\\d{2}/\\d{2}/\\d{4}")) {
System.out.println("无效格式");
valid = false;
}
} while (!valid); // 只要 valid 为 false 就循环
System.out.println(dateString);
}
}
示例运行：
输入格式为 dd/MM/yyyy 的日期：09/09/20
无效格式
输入格式为 dd/MM/yyyy 的日期：09/09/2020
09/09/2020
正则表达式解释：
\d表示数字X{n}表示X恰好出现n次
英文:
I recommend you switch from the outdated and error-prone java.util date-time API and SimpleDateFormat to the modern java.time date-time API and the corresponding formatting API (package, java.time.format). Learn more about the modern date-time API from Trail: Date Time.
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));
}
}
A sample run:
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
Regex Solution:
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);
}
}
A sample run:
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
Explanation of the regex:
\dspecifies a digitX{n}speciifiesX, exactly n times
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