PDFBOX-6107: format year with 4 digits

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1930067 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

xmpbox/src/main/java/org/apache/xmpbox/DateConverter.java

@@ -295,7 +295,7 @@ public static String toISO8601(Calendar cal, boolean printMillis)
     {
         StringBuilder retval = new StringBuilder();
 
-        retval.append(cal.get(Calendar.YEAR));
+        retval.append(String.format(Locale.US, "%04d", cal.get(Calendar.YEAR)));
         retval.append('-');
         retval.append(String.format(Locale.US, "%02d", cal.get(Calendar.MONTH) + 1));
         retval.append('-');

xmpbox/src/test/java/org/apache/xmpbox/DateConverterTest.java

@@ -133,5 +133,9 @@ void testDateFormatting() throws IOException
         assertEquals(dateFormat.format(cal.getTime()), 
                     dateFormat.format(DateConverter.toCalendar(DateConverter.toISO8601(cal,true)).getTime())
                 );
+
+        // PDFBOX-6107
+        cal = DateConverter.toCalendar("0000-01-01");
+        assertEquals("0001-01-01T00:00:00+01:00", DateConverter.toISO8601(cal));
     }
 }