Java LocalDateTime 在解析时丢弃零？ [重复]

Question

我正在将

String

解析为

LocalDateTime

并以相反的方式返回。但解析器正在删除时间的 seconds 部分的零。

这个问题与另一个问题相关（不相同）。不过，我再次发布它，因为接受的响应提到使用

DateTimeFormatter

，我已经在使用它，您可以在下面的代码中看到我在

ISO_8601_PATTERN

变量中指定秒数。

我不确定我错过了什么或者我做错了什么。

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;

public class Main
{
    private final static String DEFAULT_PATTERN = "yyyy/MM/dd";
    private final static String ISO_8601_PATTERN = "yyyy-MM-dd'T'HH:mm:ss'Z'";
    private final static String UTC_ZONE_ID = "UTC";
    
    public static void main(String[] args) {
        String stringDateTime = "2022-03-14T21:38:00Z";
        LocalDateTime dateTime = fromIso8601(stringDateTime);
        stringDateTime = toIso8601(dateTime);
        System.out.println(stringDateTime);
        // Prints: 2022-03-14T21:38Z
        // Should print: 2022-03-14T21:38:00Z
    }
    
    public static LocalDateTime fromIso8601(String dateTimeString) {
        return LocalDateTime.parse(dateTimeString, 
            DateTimeFormatter.ofPattern(ISO_8601_PATTERN).withZone(ZoneId.of(UTC_ZONE_ID)));
    }

    public static String toIso8601(LocalDateTime dateTime) {
        return dateTime.atZone(ZoneOffset.UTC).toString();
    }
    
}

Answer 1

使用 DateTimeFormatter 而不是 toString：

private final static String ISO_8601_PATTERN = "yyyy-MM-dd'T'HH:mm:ss'Z'";
public static String toIso8601(LocalDateTime dateTime) {
    return DateTimeFormatter.ofPattern(ISO_8601_PATTERN).format(dateTime);
    
}

toString()

方法不添加零值：

//-----------------------------------------------------------------------
/**
 * Outputs this time as a {@code String}, such as {@code 10:15}.
 * <p>
 * The output will be one of the following ISO-8601 formats:
 * <ul>
 * <li>{@code HH:mm}</li>
 * <li>{@code HH:mm:ss}</li>
 * <li>{@code HH:mm:ss.SSS}</li>
 * <li>{@code HH:mm:ss.SSSSSS}</li>
 * <li>{@code HH:mm:ss.SSSSSSSSS}</li>
 * </ul>
 * The format used will be the shortest that outputs the full value of
 * the time where the omitted parts are implied to be zero.
 *
 * @return a string representation of this time, not null
 */
@Override
public String toString() {
    StringBuilder buf = new StringBuilder(18);
    int hourValue = hour;
    int minuteValue = minute;
    int secondValue = second;
    int nanoValue = nano;
    buf.append(hourValue < 10 ? "0" : "").append(hourValue)
        .append(minuteValue < 10 ? ":0" : ":").append(minuteValue);
    if (secondValue > 0 || nanoValue > 0) {
        buf.append(secondValue < 10 ? ":0" : ":").append(secondValue);
        if (nanoValue > 0) {
            buf.append('.');
            if (nanoValue % 1000_000 == 0) {
                buf.append(Integer.toString((nanoValue / 1000_000) + 1000).substring(1));
            } else if (nanoValue % 1000 == 0) {
                buf.append(Integer.toString((nanoValue / 1000) + 1000_000).substring(1));
            } else {
                buf.append(Integer.toString((nanoValue) + 1000_000_000).substring(1));
            }
        }
    }
    return buf.toString();
}