Optimize InstantDeserializer replaceZeroOffsetAsZIfNecessary

Avoid expensive regex matcher allocations when replacing zero offset
with 'Z'.

OpenJDK 17 on x64 Intel(R) Xeon(R) Platinum 8259CL CPU @ 2.50GHz
Benchmark                           Mode  Cnt    Score   Error  Units
InstantDeserializerBenchmark.index  avgt    5   19.543 ± 1.384  ns/op
InstantDeserializerBenchmark.regex  avgt    5  155.081 ± 3.234  ns/op

OpenJDK 17 on aarch64 Apple M1 Pro aarch64
Benchmark                           Mode  Cnt   Score   Error  Units
InstantDeserializerBenchmark.index  avgt    5  16.855 ± 0.537  ns/op
InstantDeserializerBenchmark.regex  avgt    5  58.155 ± 1.444  ns/op

Author: schlosna

datetime/src/main/java/com/fasterxml/jackson/datatype/jsr310/deser/InstantDeserializer.java

@@ -54,13 +54,6 @@ public class InstantDeserializer<T extends Temporal>
 {
     private static final long serialVersionUID = 1L;
 
-    /**
-     * Constants used to check if the time offset is zero. See [jackson-modules-java8#18]
-     *
-     * @since 2.9.0
-     */
-    private static final Pattern ISO8601_UTC_ZERO_OFFSET_SUFFIX_REGEX = Pattern.compile("\\+00:?(00)?$");
-
     /**
      * Constants used to check if ISO 8601 time string is colonless. See [jackson-modules-java8#131]
      *
@@ -226,7 +219,7 @@ public T deserialize(JsonParser parser, DeserializationContext context) throws I
                 return (T) parser.getEmbeddedObject();
 
             case JsonTokenId.ID_START_ARRAY:
-            	return _deserializeFromArray(parser, context);
+                return _deserializeFromArray(parser, context);
         }
         return _handleUnexpectedToken(context, parser, JsonToken.VALUE_STRING,
                 JsonToken.VALUE_NUMBER_INT, JsonToken.VALUE_NUMBER_FLOAT);
@@ -337,12 +330,31 @@ private ZoneId getZone(DeserializationContext context)
     private String replaceZeroOffsetAsZIfNecessary(String text)
     {
         if (replaceZeroOffsetAsZ) {
-            return ISO8601_UTC_ZERO_OFFSET_SUFFIX_REGEX.matcher(text).replaceFirst("Z");
+            return replaceZeroOffsetAsZ(text);
         }
 
         return text;
     }
 
+    private static String replaceZeroOffsetAsZ(String text)
+    {
+        int plusIndex = text.lastIndexOf('+');
+        if (plusIndex < 0) {
+            return text;
+        }
+        int maybeOffsetIndex = plusIndex + 1;
+        int remaining = text.length() - maybeOffsetIndex;
+        if (remaining < 2 || remaining == 3 || remaining > 5) {
+            return text;
+        }
+
+        String maybeOffset = text.substring(maybeOffsetIndex);
+        if ("00".equals(maybeOffset) || "0000".equals(maybeOffset) || "00:00".equals(maybeOffset)) {
+            return text.substring(0, plusIndex) + 'Z';
+        }
+        return text;
+    }
+
     // @since 2.13
     private String addInColonToOffsetIfMissing(String text)
     {