Minor tweaks after #2556 (no functional changes)

src/main/java/com/fasterxml/jackson/databind/jsontype/impl/TypeNameIdResolver.java

@@ -15,46 +15,55 @@ public class TypeNameIdResolver extends TypeIdResolverBase
     protected final MapperConfig<?> _config;
 
     /**
-     * Mappings from class name to type id, used for serialization
+     * Mappings from class name to type id, used for serialization.
+     *<p>
+     * Since lazily constructed will require synchronization (either internal
+     * by type, or external)
      */
-    protected final Map<String, String> _typeToId;
+    protected final ConcurrentHashMap<String, String> _typeToId;
 
     /**
-     * Mappings from type id to JavaType, used for deserialization
+     * Mappings from type id to JavaType, used for deserialization.
+     *<p>
+     * Eagerly constructed, not modified, can use regular unsynchronized {@link Map}.
      */
     protected final Map<String, JavaType> _idToType;
 
     protected TypeNameIdResolver(MapperConfig<?> config, JavaType baseType,
-            Map<String, String> typeToId, Map<String, JavaType> idToType)
+            ConcurrentHashMap<String, String> typeToId,
+            HashMap<String, JavaType> idToType)
     {
         super(baseType, config.getTypeFactory());
         _config = config;
-        _typeToId = new ConcurrentHashMap<String, String>(typeToId);
-        _idToType = new ConcurrentHashMap<String, JavaType>(idToType);
+        _typeToId = typeToId;
+        _idToType = idToType;
     }
- 
+
     public static TypeNameIdResolver construct(MapperConfig<?> config, JavaType baseType,
             Collection<NamedType> subtypes, boolean forSer, boolean forDeser)
     {
         // sanity check
         if (forSer == forDeser) throw new IllegalArgumentException();
-        Map<String, String> typeToId = null;
-        Map<String, JavaType> idToType = null;
+
+        final ConcurrentHashMap<String, String> typeToId;
+        final HashMap<String, JavaType> idToType;
 
         if (forSer) {
-            typeToId = new HashMap<String, String>();
-        }
-        if (forDeser) {
-            idToType = new HashMap<String, JavaType>();
+            // Only need Class-to-id for serialization; but synchronized since may be
+            // lazily built (if adding type-id-mappings dynamically)
+            typeToId = new ConcurrentHashMap<>();
+            idToType = null;
+        } else {
+            idToType = new HashMap<>();
             // 14-Apr-2016, tatu: Apparently needed for special case of `defaultImpl`;
-            //    see [databind#1198] for details.
-            typeToId = new TreeMap<String, String>();
+            //    see [databind#1198] for details: but essentially we only need room
+            //    for a single value.
+            typeToId = new ConcurrentHashMap<>(4);
         }
         if (subtypes != null) {
             for (NamedType t : subtypes) {
-                /* no name? Need to figure out default; for now, let's just
-                 * use non-qualified class name
-                 */
+                // no name? Need to figure out default; for now, let's just
+                // use non-qualified class name
                 Class<?> cls = t.getType();
                 String id = t.hasName() ? t.getName() : _defaultTypeId(cls);
                 if (forSer) {

src/test/java/com/fasterxml/jackson/databind/jsontype/ext/ExternalTypeId198Test.java → src/test/java/com/fasterxml/jackson/databind/jsontype/ext/ExternalTypeId1198Test.java

@@ -6,7 +6,8 @@
 
 import com.fasterxml.jackson.databind.*;
 
-public class ExternalTypeId198Test extends BaseMapTest
+// [databind#1198]
+public class ExternalTypeId1198Test extends BaseMapTest
 {
     public enum Attacks { KICK, PUNCH }