More tweaking of JDK serializability

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/ObjectMapper.java

@@ -170,12 +170,29 @@ public ObjectMapper build() {
 
         @Override
         protected MapperBuilderState _saveState() {
-            return new MapperBuilderState(this);
+            return new StateImpl(this);
         }
 
         public Builder(MapperBuilderState state) {
             super(state);
         }
+
+        /**
+         * We also need actual instance of state as base class can not implement logic
+         * for reinstating mapper (via mapper builder) from state.
+         */
+        static class StateImpl extends MapperBuilderState {
+            private static final long serialVersionUID = 3L;
+
+            public StateImpl(Builder b) {
+                super(b);
+            }
+
+            @Override
+            protected Object readResolve() {
+                return new Builder(this).build();
+            }
+        }
     }
 
     /*
@@ -341,7 +358,7 @@ public Builder(MapperBuilderState state) {
 
     /*
     /**********************************************************************
-    /* Life-cycle: constructing instance
+    /* Life-cycle: legacy constructors
     /**********************************************************************
      */
 
@@ -363,6 +380,12 @@ public ObjectMapper(TokenStreamFactory streamFactory) {
         this(new Builder(streamFactory));
     }
 
+    /*
+    /**********************************************************************
+    /* Life-cycle: builder-style construction
+    /**********************************************************************
+     */
+
     /**
      * Constructor usually called either by {@link MapperBuilder#build} or
      * by sub-class constructor: will get all the settings through passed-in
@@ -443,6 +466,27 @@ public <M extends ObjectMapper, B extends MapperBuilder<M,B>> MapperBuilder<M,B>
         return (MapperBuilder<M,B>) new ObjectMapper.Builder(_savedBuilderState);
     }
 
+    /*
+    /**********************************************************************
+    /* Life-cycle: JDK serialization support
+    /**********************************************************************
+     */
+
+    // Logic here is simple: instead of serializing mapper via its contents,
+    // we have pre-packaged `MapperBuilderState` in a way that makes serialization
+    // easier, and we go with that.
+    // But note that return direction has to be supported, then, by that state object
+    // and NOT anything in here.
+
+    Object writeReplace() {
+        return _savedBuilderState;
+    }
+
+    // Just as a sanity check verify there is no attempt at directly instantiating mapper here
+    Object readResolve() {
+        throw new IllegalStateException("Should never deserialize `ObjectMapper` directly");
+    }
+
     /*
     /**********************************************************************
     /* Versioned impl

src/main/java/com/fasterxml/jackson/databind/cfg/MapperBuilderState.java

@@ -23,8 +23,11 @@
  * {@link MapperBuilder} before modules are configured and resulting
  * {@link com.fasterxml.jackson.databind.ObjectMapper} isn't constructed.
  * It is passed to mapper to allow "re-building" via newly created builder.
+ *<p>
+ * Note that JDK serialization is supported by switching this object in place
+ * of mapper. This requires some acrobatics on return direction.
  */
-public class MapperBuilderState
+public abstract class MapperBuilderState
     implements java.io.Serializable // important!
 {
     private static final long serialVersionUID = 3L;
@@ -105,7 +108,7 @@ public class MapperBuilderState
 
     /*
     /**********************************************************************
-    /* Life-cycle
+    /* Construction
     /**********************************************************************
      */
 
@@ -161,4 +164,16 @@ private static com.fasterxml.jackson.databind.Module[] _toArray(Collection<?> co
         }
         return coll.toArray(new com.fasterxml.jackson.databind.Module[coll.size()]);
     }
+
+    /*
+    /**********************************************************************
+    /* JDK deserialization support
+    /**********************************************************************
+     */
+
+    /**
+     * Method required to support JDK deserialization; made `abstract` here to ensure
+     * sub-classes must implement it.
+     */
+    protected abstract Object readResolve();
 }

src/main/java/com/fasterxml/jackson/databind/type/TypeBindings.java

@@ -36,8 +36,6 @@ public class TypeBindings
 
     /**
      * Names of potentially unresolved type variables.
-     *
-     * @since 2.3
      */
     private final String[] _unboundVariables;