Java: Convert "Europe/London" to 3 digit timezone

Question

How can I convert the timezone identifiers to the corresponding 3 digit string? For example "Europe/London" => "GMT"

Solution

See the String getDisplayName(boolean daylight,int style) method in java.util.TimeZone. The style may be TimeZone.LONG or TimeZone.SHORT with the short style returning the short name of the time zone.

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A more long winded approach is to check the output of String[] TimeZone.getAvailableIDs(int offset). The short time zone codes can be ambiguous or redundant, so maybe you might want to be more thorough about it:

TimeZone tz = TimeZone.getTimeZone("Europe/London");
for (String s : TimeZone.getAvailableIDs(tz.getOffset(System.currentTimeMillis()))) {
    System.out.print(s + ",");
}

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Africa/Abidjan,Africa/Accra,Africa/Bamako,Africa/Banjul,Africa/Bissau,
Africa/Casablanca,Africa/Conakry,Africa/Dakar,Africa/El_Aaiun,Africa/Freetown,
Africa/Lome,Africa/Monrovia,Africa/Nouakchott,Africa/Ouagadougou,Africa/Sao_Tome,
Africa/Timbuktu,America/Danmarkshavn,Atlantic/Canary,Atlantic/Faeroe,
Atlantic/Faroe,Atlantic/Madeira,Atlantic/Reykjavik,Atlantic/St_Helena,
Eire,Etc/GMT,Etc/GMT+0,Etc/GMT-0,Etc/GMT0,Etc/Greenwich,Etc/UCT,
Etc/UTC,Etc/Universal,Etc/Zulu,Europe/Belfast,
Europe/Dublin,Europe/Guernsey,Europe/Isle_of_Man,Europe/Jersey,Europe/Lisbon,
Europe/London,GB,GB-Eire,GMT,GMT0,Greenwich,Iceland,Portugal,UCT,UTC,
Universal,WET,Zulu,