Resolves #291 (regression tests added)

api/src/main/java/io/jsonwebtoken/lang/DateFormats.java

@@ -4,6 +4,7 @@ import java.text.DateFormat;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.TimeZone;
 
 /**
  * @since 0.10.0
@@ -17,14 +18,18 @@ public class DateFormats {
     private static final ThreadLocal<DateFormat> ISO_8601 = new ThreadLocal<DateFormat>() {
         @Override
         protected DateFormat initialValue() {
-            return new SimpleDateFormat(ISO_8601_PATTERN);
+            SimpleDateFormat format = new SimpleDateFormat(ISO_8601_PATTERN);
+            format.setTimeZone(TimeZone.getTimeZone("UTC"));
+            return format;
         }
     };
 
     private static final ThreadLocal<DateFormat> ISO_8601_MILLIS = new ThreadLocal<DateFormat>() {
         @Override
         protected DateFormat initialValue() {
-            return new SimpleDateFormat(ISO_8601_MILLIS_PATTERN);
+            SimpleDateFormat format = new SimpleDateFormat(ISO_8601_MILLIS_PATTERN);
+            format.setTimeZone(TimeZone.getTimeZone("UTC"));
+            return format;
         }
     };
 

api/src/test/groovy/io/jsonwebtoken/lang/DateFormatsTest.groovy

@@ -0,0 +1,25 @@
+package io.jsonwebtoken.lang
+
+import org.junit.Test
+
+import java.text.SimpleDateFormat
+
+import static org.junit.Assert.*
+
+class DateFormatsTest {
+
+    @Test //https://github.com/jwtk/jjwt/issues/291
+    void testUtcTimezone() {
+
+        def iso8601 = DateFormats.ISO_8601.get()
+        def iso8601Millis = DateFormats.ISO_8601_MILLIS.get()
+
+        assertTrue iso8601 instanceof SimpleDateFormat
+        assertTrue iso8601Millis instanceof SimpleDateFormat
+
+        def utc = TimeZone.getTimeZone("UTC")
+
+        assertEquals utc, iso8601.getTimeZone()
+        assertEquals utc, iso8601Millis.getTimeZone()
+    }
+}