Deserialization will no longer call the default constructor or InstanceCreator if the object being deserialized has a custom deserializer.

gson/src/main/java/com/google/gson/JsonDeserializationContextDefault.java

@@ -70,8 +70,7 @@ final class JsonDeserializationContextDefault implements JsonDeserializationCont
       JsonDeserializationContext context) throws JsonParseException {
     JsonObjectDeserializationVisitor<T> visitor = new JsonObjectDeserializationVisitor<T>(
         jsonObject, typeOfT, navigatorFactory, objectConstructor, deserializers, context);
-    Object target = visitor.getTarget();
-    ObjectNavigator on = navigatorFactory.create(target, typeOfT);
+    ObjectNavigator on = navigatorFactory.create(null, typeOfT);
     on.accept(visitor);
     return visitor.getTarget();
   }

gson/src/main/java/com/google/gson/JsonDeserializationVisitor.java

@@ -52,7 +52,7 @@ abstract class JsonDeserializationVisitor<T> implements ObjectNavigator.Visitor
     this.context = context;
   }
 
-  T getTarget() {
+  public T getTarget() {
     if (target == null) {
       target = constructTarget();
     }

gson/src/main/java/com/google/gson/JsonSerializationVisitor.java

@@ -44,6 +44,10 @@ final class JsonSerializationVisitor implements ObjectNavigator.Visitor {
     this.serializers = serializers;
     this.context = context;
   }
+  
+  public Object getTarget() {
+    return null;
+  }
 
   public void startVisitingObject(Object node) {
     assignToRoot(new JsonObject());

gson/src/main/java/com/google/gson/ObjectNavigator.java

@@ -59,6 +59,11 @@ final class ObjectNavigator {
      * This is called to visit a field of the current object using a custom handler
      */
     public boolean visitFieldUsingCustomHandler(Field f, Type actualTypeOfField, Object parent);
+    
+    /**
+     * Retrieve the current target
+     */
+    Object getTarget();
   }
 
   private final ExclusionStrategy exclusionStrategy;
@@ -88,38 +93,39 @@ final class ObjectNavigator {
    * If a field is null, it does not get visited.
    */
   public void accept(Visitor visitor) {
-    if (obj == null) {
-      return;
-    }
-    TypeInfo objTypeInfo = new TypeInfo(objType);
-    if (exclusionStrategy.shouldSkipClass(objTypeInfo.getRawClass())) {
-      return;
-    }
-
-    if (ancestors.contains(obj)) {
-      throw new IllegalStateException("Circular reference found: " + obj);
-    }
-    ancestors.push(obj);
-
-    try {
-      boolean visitedWithCustomHandler = visitor.visitUsingCustomHandler(obj, objType);
-      if (!visitedWithCustomHandler) {
+    boolean visitedWithCustomHandler = visitor.visitUsingCustomHandler(obj, objType);
+    if (!visitedWithCustomHandler) {
+      Object objectToVisit = (obj == null) ? visitor.getTarget() : obj;
+      if (objectToVisit == null) {
+        return;
+      }
+      TypeInfo objTypeInfo = new TypeInfo(objType);
+      if (exclusionStrategy.shouldSkipClass(objTypeInfo.getRawClass())) {
+        return;
+      }
+  
+      if (ancestors.contains(objectToVisit)) {
+        throw new IllegalStateException("Circular reference found: " + objectToVisit);
+      }
+      ancestors.push(objectToVisit);
+  
+      try {
         if (objTypeInfo.isArray()) {
-          visitor.visitArray(obj, objType);
+          visitor.visitArray(objectToVisit, objType);
         } else {
-          visitor.startVisitingObject(obj);
+          visitor.startVisitingObject(objectToVisit);
           // For all classes in the inheritance hierarchy (including the current class),
           // visit all fields
           for (Class<?> curr = objTypeInfo.getRawClass();
           curr != null && !curr.equals(Object.class); curr = curr.getSuperclass()) {
             if (!curr.isSynthetic()) {
-              navigateClassFields(obj, curr, visitor);
+              navigateClassFields(objectToVisit, curr, visitor);
             }
           }
         }
+      } finally {
+        ancestors.pop();
       }
-    } finally {
-      ancestors.pop();
     }
   }
 

gson/src/test/java/com/google/gson/functional/CustomDeserializerTest.java

@@ -0,0 +1,105 @@
+/*
+ * Copyright (C) 2008 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.functional;
+
+import java.lang.reflect.Type;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+
+import junit.framework.TestCase;
+
+/**
+ * Functional Test exercising custom deserialization only.  When test applies to both 
+ * serialization and deserialization then add it to CustomTypeAdapterTest.
+ *
+ * @author Joel Leitch
+ */
+public class CustomDeserializerTest extends TestCase {
+  private static final String DEFAULT_VALUE = "test123";
+  private static final String SUFFIX = "blah";
+  
+  private Gson gson;
+  
+  @Override
+  protected void setUp() throws Exception {
+    super.setUp();
+    gson = new GsonBuilder().registerTypeAdapter(DataHolder.class, new DataHolderDeserializer()).create();
+  }
+  
+  public void testDefaultConstructorNotCalledOnObject() throws Exception {
+    DataHolder data = new DataHolder(DEFAULT_VALUE);
+    String json = gson.toJson(data);
+    
+    DataHolder actual = gson.fromJson(json, DataHolder.class);
+    assertEquals(DEFAULT_VALUE + SUFFIX, actual.getData());
+  }
+  
+  public void testDefaultConstructorNotCalledOnField() throws Exception {
+    DataHolderWrapper dataWrapper = new DataHolderWrapper(new DataHolder(DEFAULT_VALUE));
+    String json = gson.toJson(dataWrapper);
+    
+    DataHolderWrapper actual = gson.fromJson(json, DataHolderWrapper.class);
+    assertEquals(DEFAULT_VALUE + SUFFIX, actual.getWrappedData().getData());
+  }
+
+  private static class DataHolder {
+    private final String data;
+
+    public DataHolder() {
+      throw new IllegalStateException();
+    }
+    
+    public DataHolder(String data) {
+      this.data = data;
+    }
+    
+    public String getData() {
+      return data;
+    }
+  }
+  
+  private static class DataHolderWrapper {
+    private final DataHolder wrappedData;
+    
+    public DataHolderWrapper() {
+      this(new DataHolder(DEFAULT_VALUE));
+    }
+    
+    public DataHolderWrapper(DataHolder data) {
+      this.wrappedData = data;
+    }
+
+    public DataHolder getWrappedData() {
+      return wrappedData;
+    }
+  }
+  
+  private static class DataHolderDeserializer implements JsonDeserializer<DataHolder> {
+    public DataHolder deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
+        throws JsonParseException {
+      JsonObject jsonObj = json.getAsJsonObject();
+      String dataString = jsonObj.get("data").getAsString();
+      return new DataHolder(dataString + SUFFIX);
+    }
+  }
+}