我有一个问题需要解决，但我不知道如何解决？
我必须这样做:
ShowCurrentTime.java, gives a program that displays the current time in GMT. Revise the program so that it prompts the user to enter the time zone offset to GMT and displays the time in the specified time zone.
这是一个示例运行:
到目前为止，我已经完成了默认的 GMT 时间，但我不知道如何做到这一点..
package ex;
import java.util.*;
import java.text.*;
public class GMT {
public static void main(String[] args) {
final Date currentTime = new Date();
final SimpleDateFormat sdf = new SimpleDateFormat("EEE, MMM d, yyyy hh:mm:ss a z");
sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
System.out.println("GMT time: " + sdf.format(currentTime));
}
}
最佳答案
简介
我已经放弃了对这个新的和改进的代码的原始答案。我从头开始重写了所有内容。
程序不仅可以根据时区id设置时区，还可以解析GMT偏移小时和分钟。您甚至可以输入部分小时(带或不带分钟)!该代码非常动态，因为它使用正则表达式来解释 GMT 偏移时间。我尝试尽可能全面。
以下输出是由下面编写的代码生成的。
Current time: Sat, Mar 22, 2014 07:12:22 PM EDT (GMT+00:00)
Enter a timezone: Africa/Cairo
Sun, Mar 23, 2014 01:12:22 AM EET (Eastern European Time)
Continue? (y/n): y
Enter a timezone: America/Los_Angeles
Sat, Mar 22, 2014 04:12:22 PM PDT (Pacific Standard Time)
Continue? (y/n): y
Enter a timezone: GMT-05:00
Sat, Mar 22, 2014 06:12:22 PM GMT-05:00 (GMT-05:00)
Continue? (y/n): y
Enter a timezone: GMT-4:30
Sat, Mar 22, 2014 06:42:22 PM GMT-04:30 (GMT-04:30)
Continue? (y/n): y
Enter a timezone: 8
Sun, Mar 23, 2014 07:12:22 AM GMT+08:00 (GMT+08:00)
Continue? (y/n): y
Enter a timezone: 11:30
Sun, Mar 23, 2014 10:42:22 AM GMT+11:30 (GMT+11:30)
Continue? (y/n): y
Enter a timezone: FooBar
[ERROR] Could not parse GMT ID!
[ERROR] Invalid GMT TimeZone ID!
Sun, Mar 23, 2014 10:42:22 AM GMT+11:30 (GMT+11:30)
Continue? (y/n): y
Enter a timezone: Asia/Tokyo
Sun, Mar 23, 2014 08:12:22 AM JST (Japan Standard Time)
Continue? (y/n): n
Done...
完整示例:
下面的代码应该可以满足您的要求甚至更多!
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import java.util.TimeZone;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class TimeZoneFormatter {
private static final DateFormat DEFAULT_DATE_FORMAT = new SimpleDateFormat("EEE, MMM d, yyyy hh:mm:ss a z");
private static final TimeZone GMT_TIME_ZONE = TimeZone.getTimeZone("GMT+00:00");
private static final Pattern GMT_PATTERN = Pattern.compile("(?:GMT)?([+-])?([012]?\\d)(:([0-5]?\\d))?");
private static final Pattern REMOVE_LEADING_ZEROS = Pattern.compile("^0+(?!$)");
private static final Set<String> VALID_IDS = new LinkedHashSet<String>(Arrays.asList(TimeZone.getAvailableIDs()));
private static final boolean DEBUG = true;
private DateFormat dateFormat;
private TimeZone timeZone;
public TimeZoneFormatter() {
this(DEFAULT_DATE_FORMAT);
}
public TimeZoneFormatter(DateFormat dateFormat) {
this.dateFormat = dateFormat;
this.timeZone = GMT_TIME_ZONE;
}
public void setDateFormat(DateFormat dateFormat) {
this.dateFormat = dateFormat;
}
public void setTimezone(boolean positive, int hours, int minutes) {
String timeZoneId = formatGmtId(positive, hours, minutes);
setTimezone(timeZoneId);
}
public void setTimezone(String timeZoneId) {
TimeZone newTimeZone = TimeZone.getTimeZone(timeZoneId);
if (timeZone.getRawOffset() != 0 && newTimeZone.getRawOffset() == 0) {
System.out.println("[ERROR] Invalid GMT TimeZone ID!");
} else {
timeZone = newTimeZone;
dateFormat.setTimeZone(timeZone);
}
}
public DateFormat getDateFormat() {
return dateFormat;
}
public String getTimezoneId() {
return timeZone.getID();
}
// -------------------------------------------------------------------------
// Begin internal parsing and formatting methods.
// -------------------------------------------------------------------------
private String parseGmtTimeZoneId(String id) {
Matcher m = GMT_PATTERN.matcher(id);
if (m.find()) {
char sign = m.group(1) != null ? m.group(1).charAt(0) : '+';
int hours = removeLeadingZeros(m.group(2));
int minutes = 0;
if (m.group(3) != null) {
minutes = removeLeadingZeros(m.group(4));
}
return formatGmtId(sign, hours, minutes);
}
if (!VALID_IDS.contains(id)) {
System.out.println("[ERROR] Could not parse GMT ID!");
}
return id;
}
private void setGmtTimezone(String gmtOffset) {
String timeZoneId = parseGmtTimeZoneId(gmtOffset);
setTimezone(timeZoneId);
}
private String formatGmtId(boolean positive, int hours, int minutes) {
return formatGmtId(positive ? '+' : '-', hours, minutes);
}
private String formatGmtId(char sign, int hours, int minutes) {
return String.format("GMT%c%02d:%02d", sign, hours, minutes);
}
private int removeLeadingZeros(String intStr) {
return Integer.parseInt(intStr.replaceAll(REMOVE_LEADING_ZEROS.pattern(), ""));
}
private String formatDate(final Date time) {
return String.format("%s (%s)", dateFormat.format(time),
timeZone.getDisplayName());
}
// -------------------------------------------------------------------------
// Begin main method and other static utility methods.
// -------------------------------------------------------------------------
public static void main(String[] args) {
if (DEBUG) {
printAllAvailableTimeZones();
}
final Date time = new Date();
TimeZoneFormatter frmt = new TimeZoneFormatter();
Scanner scan = new Scanner(System.in);
try {
System.out.printf("Current time: ");
printDate(time, frmt);
while (true) {
System.out.print("Enter a timezone: ");
frmt.setGmtTimezone(scan.nextLine());
printDate(time, frmt);
System.out.print("Continue? (y/n): ");
String response = scan.nextLine().trim();
if ((response.length() < 1 ? 'y' : response.charAt(0)) == 'n') {
break;
}
}
} catch (Exception e) {
e.printStackTrace();
} finally {
scan.close();
}
System.out.println("Done...");
}
public static void printDate(final Date date, TimeZoneFormatter formatter) {
if (date == null) {
throw new IllegalArgumentException("Please enter a non-null date.");
}
if (formatter == null) {
formatter = new TimeZoneFormatter();
}
System.out.println(formatter.formatDate(date));
}
public static void printAllAvailableTimeZones() {
System.out.println("Available Time Zones:");
List<TimeZone> timeZones = new ArrayList<TimeZone>();
for (String id : VALID_IDS) {
timeZones.add(TimeZone.getTimeZone(id));
}
Collections.sort(timeZones, new Comparator<TimeZone>() {
@Override
public int compare(TimeZone t1, TimeZone t2) {
int offsetDiff = t1.getRawOffset() - t2.getRawOffset();
if (offsetDiff == 0) {
int nameDiff = t1.getDisplayName().compareTo(t2.getDisplayName());
if (nameDiff == 0) {
return t1.getID().compareTo(t2.getID());
} else {
return nameDiff;
}
} else {
return offsetDiff;
}
}
});
for (TimeZone timeZone : timeZones) {
System.out.printf("%s : %32s : %s%n", getFormattedOffset(timeZone),
timeZone.getID(), timeZone.getDisplayName());
}
System.out.println();
}
private static String getFormattedOffset(TimeZone timeZone) {
int offset = timeZone.getRawOffset();
char sign = offset < 0 ? '-' : '+';
if (offset < 0) {
offset *= -1;
}
int hours = offset / 3600000;
int mins = (offset % 3600000) / 60000;
return String.format("%c%02d:%02d", sign, hours, mins);
}
}
打印时区偏移和显示名称:
这里是所有比 GMT 时间晚 5 小时的时区的快速打印输出。这可以通过调用 printAllAvailableTimeZones() 方法来实现。这会在 DEBUG 模式下自动调用。
-05:00 : America/Bogota : Colombia Time
-05:00 : America/Havana : Cuba Standard Time
-05:00 : Cuba : Cuba Standard Time
-05:00 : America/Atikokan : Eastern Standard Time
-05:00 : America/Cayman : Eastern Standard Time
-05:00 : America/Coral_Harbour : Eastern Standard Time
-05:00 : America/Detroit : Eastern Standard Time
-05:00 : America/Fort_Wayne : Eastern Standard Time
-05:00 : America/Grand_Turk : Eastern Standard Time
-05:00 : America/Indiana/Indianapolis : Eastern Standard Time
-05:00 : America/Indiana/Marengo : Eastern Standard Time
-05:00 : America/Indiana/Petersburg : Eastern Standard Time
-05:00 : America/Indiana/Vevay : Eastern Standard Time
-05:00 : America/Indiana/Vincennes : Eastern Standard Time
-05:00 : America/Indiana/Winamac : Eastern Standard Time
-05:00 : America/Indianapolis : Eastern Standard Time
-05:00 : America/Iqaluit : Eastern Standard Time
-05:00 : America/Jamaica : Eastern Standard Time
-05:00 : America/Kentucky/Louisville : Eastern Standard Time
-05:00 : America/Kentucky/Monticello : Eastern Standard Time
-05:00 : America/Louisville : Eastern Standard Time
-05:00 : America/Montreal : Eastern Standard Time
-05:00 : America/Nassau : Eastern Standard Time
-05:00 : America/New_York : Eastern Standard Time
-05:00 : America/Nipigon : Eastern Standard Time
-05:00 : America/Panama : Eastern Standard Time
-05:00 : America/Pangnirtung : Eastern Standard Time
-05:00 : America/Port-au-Prince : Eastern Standard Time
-05:00 : America/Thunder_Bay : Eastern Standard Time
-05:00 : America/Toronto : Eastern Standard Time
-05:00 : Canada/Eastern : Eastern Standard Time
-05:00 : EST : Eastern Standard Time
-05:00 : EST5EDT : Eastern Standard Time
-05:00 : IET : Eastern Standard Time
-05:00 : Jamaica : Eastern Standard Time
-05:00 : SystemV/EST5 : Eastern Standard Time
-05:00 : SystemV/EST5EDT : Eastern Standard Time
-05:00 : US/East-Indiana : Eastern Standard Time
-05:00 : US/Eastern : Eastern Standard Time
-05:00 : US/Michigan : Eastern Standard Time
-05:00 : America/Guayaquil : Ecuador Time
-05:00 : Etc/GMT+5 : GMT-05:00
-05:00 : America/Lima : Peru Time
其他资源:
以下 Oracle 教程:Time Zone and Offset Classes可以进一步帮助您解决问题。
ZoneId and ZoneOffset
The Date-Time API provides two classes for specifying a time zone or an offset:
- ZoneId specifies a time zone identifier and provides rules for converting between an Instant and a LocalDateTime.
- ZoneOffset specifies a time zone offset from Greenwich/UTC time.
关于Java GMT 显示，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22577923/