Merge pull request #3084 from steinhauer-software/BAEL-1317

BAEl-1317: Display All Time Zones With GMT and UTC

core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java

@@ -0,0 +1,55 @@
+package com.baeldung.timezonedisplay;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.time.ZoneOffset;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class TimezoneDisplay {
+
+    public enum OffsetBase {
+        GMT, UTC
+    }
+
+    public List<String> compileListFor(OffsetBase base) {
+        Set<String> availableZoneIds = ZoneId.getAvailableZoneIds();
+
+        LocalDateTime now = LocalDateTime.now();
+        return availableZoneIds
+          .stream()
+          .map(ZoneId::of)
+          .sorted(new ZoneComparator())
+          .map(id -> String.format("(%s%s) %s", base, getOffset(now, id), id.getId()))
+          .collect(Collectors.toList());
+    }
+
+    private String getOffset(LocalDateTime dateTime, ZoneId id) {
+        return dateTime
+          .atZone(id)
+          .getOffset()
+          .getId()
+          .replace("Z", "+00:00");
+    }
+
+    private class ZoneComparator implements Comparator<ZoneId> {
+
+        @Override
+        public int compare(ZoneId zoneId1, ZoneId zoneId2) {
+            LocalDateTime now = LocalDateTime.now();
+
+            ZoneOffset offset1 = now
+              .atZone(zoneId1)
+              .getOffset();
+
+            ZoneOffset offset2 = now
+              .atZone(zoneId2)
+              .getOffset();
+
+            return offset1.compareTo(offset2);
+        }
+    }
+
+}

core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayApp.java

@@ -0,0 +1,19 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.List;
+
+public class TimezoneDisplayApp {
+
+    public static void main(String... args) {
+        TimezoneDisplay display = new TimezoneDisplay();
+
+        System.out.println("Time zones in UTC:");
+        List<String> utc = display.compileListFor(TimezoneDisplay.OffsetBase.UTC);
+        utc.forEach(System.out::println);
+
+        System.out.println("Time zones in GMT:");
+        List<String> gmt = display.compileListFor(TimezoneDisplay.OffsetBase.GMT);
+        gmt.forEach(System.out::println);
+    }
+
+}

core-java/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayJava7.java

@@ -0,0 +1,43 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
+
+public class TimezoneDisplayJava7 {
+
+    public enum OffsetBase {
+        GMT, UTC
+    }
+
+    public List<String> compileListFor(TimezoneDisplayJava7.OffsetBase base) {
+        String[] availableZoneIds = TimeZone.getAvailableIDs();
+        List<String> result = new ArrayList<>(availableZoneIds.length);
+
+        for (String zoneId : availableZoneIds) {
+            TimeZone curTimeZone = TimeZone.getTimeZone(zoneId);
+
+            String offset = calculateOffset(curTimeZone.getRawOffset());
+
+            result.add(String.format("(%s%s) %s", base, offset, zoneId));
+        }
+
+        Collections.sort(result);
+
+        return result;
+    }
+
+    private String calculateOffset(int rawOffset) {
+        if (rawOffset == 0) {
+            return "+00:00";
+        }
+        long hours = TimeUnit.MILLISECONDS.toHours(rawOffset);
+        long minutes = TimeUnit.MILLISECONDS.toMinutes(rawOffset);
+        minutes = Math.abs(minutes - TimeUnit.HOURS.toMinutes(hours));
+
+        return String.format("%+03d:%02d", hours, Math.abs(minutes));
+    }
+
+}

core-java/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayJava7App.java

@@ -0,0 +1,23 @@
+package com.baeldung.timezonedisplay;
+
+import java.util.List;
+
+public class TimezoneDisplayJava7App {
+
+    public static void main(String... args) {
+        TimezoneDisplayJava7 display = new TimezoneDisplayJava7();
+
+        System.out.println("Time zones in UTC:");
+        List<String> utc = display.compileListFor(TimezoneDisplayJava7.OffsetBase.UTC);
+        for (String timeZone : utc) {
+            System.out.println(timeZone);
+        }
+
+        System.out.println("Time zones in GMT:");
+        List<String> gmt = display.compileListFor(TimezoneDisplayJava7.OffsetBase.GMT);
+        for (String timeZone : gmt) {
+            System.out.println(timeZone);
+        }
+    }
+
+}