From d9608d20a22907ac4ccd49c7b9e6465ed7916709 Mon Sep 17 00:00:00 2001
From: Holger Steinhauer <hlibrenz@gmail.com>
Date: Sun, 19 Nov 2017 18:02:25 +0000
Subject: [PATCH] BAEL-1317: Display All Time Zones With GMT and UTC

---
 .../timezonedisplay/TimezoneDisplay.java      | 50 +++++++++++++++++++
 .../timezonedisplay/TimezoneDisplayApp.java   | 19 +++++++
 2 files changed, 69 insertions(+)
 create mode 100644 core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java
 create mode 100644 core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayApp.java

diff --git a/core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java b/core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java
new file mode 100644
index 0000000000..296f8b82f8
--- /dev/null
+++ b/core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplay.java
@@ -0,0 +1,50 @@
+package com.baeldung.timezonedisplay;
+
+import sun.util.calendar.ZoneInfo;
+
+import java.time.LocalDateTime;
+import java.time.ZoneId;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Set;
+import java.util.TimeZone;
+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) {
+            TimeZone tz1 = ZoneInfo.getTimeZone(zoneId1);
+            TimeZone tz2 = ZoneInfo.getTimeZone(zoneId2);
+
+            return Integer.compare(tz1.getRawOffset(), tz2.getRawOffset());
+        }
+    }
+
+}
diff --git a/core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayApp.java b/core-java-8/src/main/java/com/baeldung/timezonedisplay/TimezoneDisplayApp.java
new file mode 100644
index 0000000000..42a7a2ba85
--- /dev/null
+++ b/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);
+    }
+
+}