Don't return incorrect date format instance (#3576)

Author: mattcreaser

aws-android-sdk-core/src/main/java/com/amazonaws/transform/SimpleTypeJsonUnmarshallers.java

@@ -249,7 +249,7 @@ public static ByteJsonUnmarshaller getInstance() {
      */
     public static class DateJsonUnmarshaller implements Unmarshaller<Date, JsonUnmarshallerContext> {
         private static final int DATE_MULTIPLIER = 1000;
-        private final TimestampFormat format;
+        final TimestampFormat format;
 
         private DateJsonUnmarshaller(TimestampFormat format) {
             this.format = format;
@@ -286,10 +286,7 @@ public Date unmarshall(JsonUnmarshallerContext unmarshallerContext) throws Excep
          * @return the instance.
          */
         public static DateJsonUnmarshaller getInstance() {
-            if (instance == null) {
-                instance = new DateJsonUnmarshaller(TimestampFormat.UNIX_TIMESTAMP);
-            }
-            return instance;
+            return getInstance(TimestampFormat.UNIX_TIMESTAMP);
         }
 
         /**

aws-android-sdk-core/src/test/java/com/amazonaws/transform/SimpleTypeJsonUnmarshallerTest.java

@@ -256,6 +256,15 @@ public void testDateRfc822JsonUnmarshaller() throws Exception {
         assertEquals(unmarshalledDate.getTime(), date.getTime());
     }
 
+    @Test
+    public void defaultFunctionAlwaysReturnsUnixTimestampUnmarshaller() {
+        SimpleTypeJsonUnmarshallers.DateJsonUnmarshaller first =
+                SimpleTypeJsonUnmarshallers.DateJsonUnmarshaller.getInstance(TimestampFormat.ISO_8601);
+        SimpleTypeJsonUnmarshallers.DateJsonUnmarshaller second =
+                SimpleTypeJsonUnmarshallers.DateJsonUnmarshaller.getInstance();
+        assertEquals(TimestampFormat.UNIX_TIMESTAMP, second.format);
+    }
+
     @Test
     public void testDoubleJsonUnmarshaller() throws Exception {
         Double dub = new Double(5.5);