在 Java 中获取带有允许的文件名字符的完整语言环境日期和小时字符串的好方法是什么？

Question

I want to build a string with the locale date and hour, concatenated, that must be human readable and compatible with the most common OS file allowed characters as well. Something like:

6-23-20_03-06-50

I am using this as an automated filename suggestion for the user. To achieve this, I have written the following code:

public class CustomDateProvider {

    private static final String TWO_DIGIT_PATTERN = "%02d";

    public static String getDashedDateAndHourFromDate(Date date) {
        ZonedDateTime dateTime = date.toInstant().atZone(ZoneId.systemDefault());
        int hour = dateTime.getHour();
        int minute = dateTime.getMinute();
        int second = dateTime.getSecond();

        DateFormat dateFormat = DateFormat.getDateInstance(DateFormat.SHORT, Locale.getDefault());
        String localeDate = dateFormat.format(date);
        String dashedDate = localeDate.replace("/", "-");

        return dashedDate
                + "_"
                + String.format(TWO_DIGIT_PATTERN, hour)
                + "-"
                + String.format(TWO_DIGIT_PATTERN, minute)
                + "-"
                + String.format(TWO_DIGIT_PATTERN, second);
    }
}

Thus, I am assuming the date separator char will always be " / ", and I am not sure if this is always correct. Either way, there are probably better ways to achieve my goal, and I would appreciate any improvement.

Answer 1

java.time

You are using terrible date-time classes that were years ago supplanted by the modern java.time classes.

Avoid localized formats

You asked for text representing the date-time value in various localized formats. That approach is unwise in a file name.

• Localized formats may well contain characters that would be problematic on various file systems. Your example MM/dd/yyyy format using slash characters might cause problems on some Unix/ POSIX -oriented file systems.
• Localized formats may be misinterpreted by humans who assume a different custom.
• Localized formats may make difficult or impossible parsing that string back to a date-time value.

Instead, I strongly recommend using only standard ISO 8601 formats.

“Basic” variant of ISO 8601

You asked for:

must be human readable and compatible

I suggest sticking with the "basic" variant of ISO 8601 format that makes minimal use of delimiters. For compatibility with various filesystems you want to avoid slash, backslash, colon, and space characters.

The ISO 8601 format is in order of significance: year, month, day, hour, minute, second, fractional second. An uppercase T separates the date portion from the time-of-day portion. Such strings sort alphabetically as chronological.

UTC

I also suggest you stick with UTC (an offset of zero hours-minutes-seconds). For this, use Instant (or OffsetDateTime set to UTC).

Instant instant = Instant.now() ; // Capture current moment as seen in UTC.

Truncate if you do not want fractional seconds or minutes.

Instant instant = Instant.now().truncatedTo( ChronoUnit.MINUTES ) ;

You would do string manipulation to remove the hyphens between the year-month-day and the colons between the hour-minute-second.

String output = instant.replace( "-" , "" ).replace( ":" , "" ) ;

For 2021-01-23T12:30:35Z that would be:

20210123T123035Z

The trailing Z means UTC, and is pronounced “Zulu”.

Zoned moment

If you insist on using the date-time as seen in a particular time zone, use ZonedDateTime .

ZoneId z = ZoneId.systemDefault() ;  // Or ZoneId.of( "Africa/Tunis" ) and such.
ZonedDateTime zdt = ZonedDateTime.now().truncatedTo( ChronoUnit.MINUTES ) ;

Specify a formatting pattern.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "uuuuMMdd'T'HHmmss" ) ;
String output = zdt.format( f ) ;

Example:

20210123T123035

I do not recommend omitting the zone or offset, but there you go if you insist.

If you insist your example format of 6-23-20_03-06-50 , define a DateTimeFormatter to match.

DateTimeFormatter f = DateTimeFormatter.ofPattern( "M-d-uu'_'HH-mm-ss" ) ;

Allowing single-digit month or day is yet another thing I recommend against. As is the use of a two-digit year.

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About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date , Calendar , & SimpleDateFormat .

To learn more, see the Oracle Tutorial . And search Stack Overflow for many examples and explanations. Specification is JSR 310 .

The Joda-Time project, now in maintenance mode , advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes. Hibernate 5 & JPA 2.2 support java.time .

Where to obtain the java.time classes?

• Java SE 8 , Java SE 9 , Java SE 10 , Java SE 11 , and later - Part of the standard Java API with a bundled implementation.
• Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
• Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport .
• Android
• Later versions of Android bundle implementations of the java.time classes.
• For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP… .

Answer 2

Here is how you can get the locale Date_Time-

import java.time.LocalDateTime;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

public class CurrentDateTimeExample {
   public static void main(String[] args) {
       LocalDateTime currentDateTime = LocalDateTime.now();
       System.out.println("Current Date and Time: "+currentDateTime);

       DateTimeFormatter pattern = DateTimeFormatter.ofPattern("uuuu-MM-dd_hh-mm-ss");
       System.out.println("Date Time in 12 Hour format - " + currentDateTime.format(pattern));
   }
}

For more details please see this Get Locale Date_Time