英文:
Joda Time toDate() wrong result
问题
我正在使用这段代码:
date
- 来自 DatePicker
的日期对象,格式为字符串 Thu Sep 10 00:00:00 GMT+03:00 2020
mDate = DateTime(date)
.withHourOfDay(0)
.withMinuteOfHour(0)
.withSecondOfMinute(0)
.withMillisOfSecond(0)
.toDate()
结果为:
mDate
- Wed Sep 09 03:00:00 GMT+03:00 2020
这段代码有什么问题吗?
英文:
I am using this code:
date
- Date object from DatePicker
, as string Thu Sep 10 00:00:00 GMT+03:00 2020
mDate = DateTime(date)
.withHourOfDay(0)
.withMinuteOfHour(0)
.withSecondOfMinute(0)
.withMillisOfSecond(0)
.toDate()
The result
mDate
- Wed Sep 09 03:00:00 GMT+03:00 2020
What wrong with this?
答案1
得分: 2
你没有正确地将 DateTime
对象转换为 java.util.Date
。一个正确的方法是从 DateTime
对象中获取毫秒数,并使用这些毫秒数初始化 java.util.Date
。
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;
public class Main {
public static void main(String[] args) {
// 定义日期时间格式化器
DateTimeFormatter formatter = DateTimeFormat.forPattern("EEE MMM dd HH:mm:ss zZ yyyy");
// 来自DatePicker的日期时间字符串
String strDateTime = "Thu Sep 10 00:00:00 GMT+03:00 2020";
DateTime dateTime = DateTime.parse(strDateTime, formatter);
System.out.println(dateTime);
// 从 1970-01-01T00:00:00Z 开始的毫秒数
long millis = dateTime.getMillis();
System.out.println(millis);
Date mDate = new Date(millis);
// 在默认时区 (BST) 中显示 java.util.Date 对象
System.out.println(mDate);
// 在不同的时区下和使用自定义格式显示 java.util.Date
SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy");
sdf.setTimeZone(TimeZone.getTimeZone("GMT+3"));
System.out.println(sdf.format(mDate));
}
}
输出:
2020-09-09T21:00:00.000Z
1599685200000
Wed Sep 09 22:00:00 BST 2020
Thu Sep 10 00:00:00 GMT+03:00 2020
注意: java.util.Date
不表示日期/时间对象。它只表示从 1970-01-01T00:00:00Z
开始的毫秒数。它没有任何时区或区域偏移信息。当你打印它时,Java 使用你的 JVM 的时区来生成字符串。如果你想在其他时区中打印它,可以使用上面示例中展示的 SimpleDateFormat
。
我建议你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(位于 java.time.format
包中)。从 教程: 日期时间 中了解更多关于现代日期时间 API 的信息。如果你的 Android API 版本仍不符合 Java 8,可以查看 https://stackoverflow.com/questions/38922754/how-to-use-threetenabp-in-android-project 和 通过 desugaring 可用的 Java 8+ API。
下表显示了现代日期时间类的概览:
英文:
You are not converting the DateTime
object to java.util.Date
correctly. A correct way is to get the milliseconds from DateTime
object and initialize the java.util.Date
with the milliseconds.
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;
public class Main {
public static void main(String[] args) {
// Define formatter
DateTimeFormatter formatter = DateTimeFormat.forPattern("EEE MMM dd HH:mm:ss zZ yyyy");
// Date-time string from DatePicker
String strDateTime = "Thu Sep 10 00:00:00 GMT+03:00 2020";
DateTime dateTime = DateTime.parse(strDateTime, formatter);
System.out.println(dateTime);
// No. of milliseconds from the epoch of 1970-01-01T00:00:00Z
long millis = dateTime.getMillis();
System.out.println(millis);
Date mDate = new Date(millis);
// Display java.util.Date object in my default time-zone (BST)
System.out.println(mDate);
//Display java.util.Date in a different time-zone and using custom format
SimpleDateFormat sdf = new SimpleDateFormat("EEE MMM dd HH:mm:ss z yyyy");
sdf.setTimeZone(TimeZone.getTimeZone("GMT+3"));
System.out.println(sdf.format(mDate));
}
}
Output:
2020-09-09T21:00:00.000Z
1599685200000
Wed Sep 09 22:00:00 BST 2020
Thu Sep 10 00:00:00 GMT+03:00 2020
Note: java.util.Date
does not represent a Date/Time object. It simply represents the no. of milliseconds from the epoch of 1970-01-01T00:00:00Z
. It does not have any time-zone or zone-offset information. When you print it, Java prints the string obtained by applying the time-zone of your JVM. If you want to print it in some other timezone, you can do so using the SimpleDateFormat
as shown above.
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. If your Android API level is still not compliant with Java8, check https://stackoverflow.com/questions/38922754/how-to-use-threetenabp-in-android-project and Java 8+ APIs available through desugaring.
The following table shows an overview of modern date-time classes:
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