[PATCH] Support for UTC Zones with TimeZone.getTimeZone()

[Mohamed Naufal]

Hi,

I noticed that with the following data:

LocalDateTime ldt = LocalDateTime.parse("2017-01-01T00:00:00");
ZonedDateTime dt1 = ZonedDateTime.of(ldt, ZoneId.of("GMT+10"));
ZonedDateTime dt2 = ZonedDateTime.of(ldt, ZoneId.of("UTC+10"));

dt1.equals(dt2) returns true as expected, but with:

GregorianCalendar gc1 = GregorianCalendar.from(dt1);
GregorianCalendar gc2 = GregorianCalendar.from(dt2);

gc1.equals(gc2) returns false.

Looking at the code, I see when a GregorianCalendar is being constructed,
TimeZone.getTimeZone() gets called, but it doesn't recognise UTC time-zones
with offsets, and falls back to GMT(+0), whereas ZoneId treats GMT and UTC
based zones equivalently.

PFA a patch to fix this.

Thank you,
Naufal

diff -r 65464a307408 src/java.base/share/classes/java/util/TimeZone.java
--- a/src/java.base/share/classes/java/util/TimeZone.java       Thu Aug 03 
18:56:59 2017 +0000
+++ b/src/java.base/share/classes/java/util/TimeZone.java       Sat Dec 16 
10:10:14 2017 +0000
@@ -782,7 +782,8 @@
     private static volatile TimeZone defaultTimeZone;
 
     static final String         GMT_ID        = "GMT";
-    private static final int    GMT_ID_LENGTH = 3;
+    static final String         UTC_ID        = "UTC";
+    private static final int    GMT_UTC_ID_LENGTH = 3;
 
     // a static TimeZone we can reference if no AppContext is in place
     private static volatile TimeZone mainAppContextDefault;
@@ -799,9 +800,9 @@
         int length;
 
         // Error if the length of id isn't long enough or id doesn't
-        // start with "GMT".
-        if ((length = id.length()) < (GMT_ID_LENGTH + 2) ||
-            id.indexOf(GMT_ID) != 0) {
+        // start with "GMT" or "UTC".
+        if ((length = id.length()) < (GMT_UTC_ID_LENGTH + 2) ||
+            id.indexOf(GMT_ID) != 0 && id.indexOf(UTC_ID) != 0) {
             return null;
         }
 
@@ -815,7 +816,7 @@
             return zi;
         }
 
-        int index = GMT_ID_LENGTH;
+        int index = GMT_UTC_ID_LENGTH;
         boolean negative = false;
         char c = id.charAt(index++);
         if (c == '-') {