Fix the map type adapter to support array serialization natively.

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

@@ -170,8 +170,8 @@ public final class Gson {
     this(DEFAULT_EXCLUSION_STRATEGY, DEFAULT_EXCLUSION_STRATEGY, DEFAULT_NAMING_POLICY,
         DefaultTypeAdapters.getDefaultInstanceCreators(),
         false, DefaultTypeAdapters.getAllDefaultSerializers(),
-        DefaultTypeAdapters.getAllDefaultDeserializers(), DEFAULT_JSON_NON_EXECUTABLE, true, false,
+        DefaultTypeAdapters.getAllDefaultDeserializers(), false, DEFAULT_JSON_NON_EXECUTABLE, true,
-        false, LongSerializationPolicy.DEFAULT);
+        false, false, LongSerializationPolicy.DEFAULT);
   }
 
   Gson(final ExclusionStrategy deserializationExclusionStrategy,
@@ -180,8 +180,9 @@ public final class Gson {
       final ParameterizedTypeHandlerMap<InstanceCreator<?>> instanceCreators, boolean serializeNulls,
       final ParameterizedTypeHandlerMap<JsonSerializer<?>> serializers,
       final ParameterizedTypeHandlerMap<JsonDeserializer<?>> deserializers,
-      boolean generateNonExecutableGson, boolean htmlSafe, boolean prettyPrinting,
+      boolean complexMapKeySerialization, boolean generateNonExecutableGson, boolean htmlSafe,
-      boolean serializeSpecialFloatingPointValues, LongSerializationPolicy longSerializationPolicy) {
+      boolean prettyPrinting, boolean serializeSpecialFloatingPointValues,
+      LongSerializationPolicy longSerializationPolicy) {
     this.deserializationExclusionStrategy = deserializationExclusionStrategy;
     this.serializationExclusionStrategy = serializationExclusionStrategy;
     this.fieldNamingPolicy = fieldNamingPolicy;
@@ -245,12 +246,12 @@ public final class Gson {
         .factory(TypeAdapters.INET_ADDRESS_FACTORY)
         .typeAdapter(BigDecimal.class, new BigDecimalTypeAdapter())
         .typeAdapter(BigInteger.class, new BigIntegerTypeAdapter())
-        .factory(new MapTypeAdapterFactory(constructorConstructor))
         .factory(new CollectionTypeAdapterFactory(constructorConstructor))
         .factory(ObjectTypeAdapter.FACTORY)
         .factory(new GsonToMiniGsonTypeAdapterFactory(serializers, deserializers,
             new JsonDeserializationContext(this), new JsonSerializationContext(this), serializeNulls
         ))
+        .factory(new MapTypeAdapterFactory(constructorConstructor, complexMapKeySerialization))
         .factory(ArrayTypeAdapter.FACTORY)
         .factory(reflectiveTypeAdapterFactory);
 

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

@@ -28,7 +28,6 @@ import java.util.Date;
 import java.util.HashSet;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
 import java.util.Set;
 
 /**
@@ -65,8 +64,6 @@ import java.util.Set;
  * @author Joel Leitch
  */
 public final class GsonBuilder {
-  private static final MapAsArrayTypeAdapter COMPLEX_KEY_MAP_TYPE_ADAPTER =
-      new MapAsArrayTypeAdapter();
   private static final InnerClassExclusionStrategy innerClassExclusionStrategy =
       new InnerClassExclusionStrategy();
   private static final ExposeAnnotationDeserializationExclusionStrategy
@@ -94,6 +91,7 @@ public final class GsonBuilder {
   private String datePattern;
   private int dateStyle;
   private int timeStyle;
+  private boolean complexMapKeySerialization = false;
   private boolean serializeSpecialFloatingPointValues;
   private boolean escapeHtmlChars;
   private boolean prettyPrinting;
@@ -273,7 +271,7 @@ public final class GsonBuilder {
    * @since 1.7
    */
   public GsonBuilder enableComplexMapKeySerialization() {
-    registerTypeHierarchyAdapter(Map.class, COMPLEX_KEY_MAP_TYPE_ADAPTER);
+    complexMapKeySerialization = true;
     return this;
   }
 
@@ -694,8 +692,9 @@ public final class GsonBuilder {
     return new Gson(new DisjunctionExclusionStrategy(deserializationStrategies),
         new DisjunctionExclusionStrategy(serializationStrategies),
         fieldNamingPolicy, instanceCreators, serializeNulls,
-        customSerializers, customDeserializers, generateNonExecutableJson, escapeHtmlChars,
+        customSerializers, customDeserializers, complexMapKeySerialization,
-        prettyPrinting, serializeSpecialFloatingPointValues, longSerializationPolicy);
+        generateNonExecutableJson, escapeHtmlChars, prettyPrinting,
+        serializeSpecialFloatingPointValues, longSerializationPolicy);
   }
 
   private static void addTypeAdaptersForDate(String datePattern, int dateStyle, int timeStyle,

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

@@ -1,102 +0,0 @@
-/*
- * Copyright (C) 2010 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;
-
-import java.lang.reflect.Type;
-import java.util.Map;
-
-/**
- * Adapts maps containing complex keys as arrays of map entries.
- *
- * <h3>Maps as JSON objects</h3>
- * The standard GSON map type adapter converts Java {@link Map Maps} to JSON
- * Objects. This requires that map keys can be serialized as strings; this is
- * insufficient for some key types. For example, consider a map whose keys are
- * points on a grid. The default JSON form encodes reasonably: <pre>   {@code
- *   Map<Point, String> original = new LinkedHashMap<Point, String>();
- *   original.put(new Point(5, 6), "a");
- *   original.put(new Point(8, 8), "b");
- *   System.out.println(gson.toJson(original, type));
- * }</pre>
- * The above code prints this JSON object:<pre>   {@code
- *   {
- *     "(5,6)": "a",
- *     "(8,8)": "b"
- *   }
- * }</pre>
- * But GSON is unable to deserialize this value because the JSON string name is
- * just the {@link Object#toString() toString()} of the map key. Attempting to
- * convert the above JSON to an object fails with a parse exception:
- * <pre>com.google.gson.JsonParseException: Expecting object found: "(5,6)"
- *   at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
- *   at com.google.gson.ObjectNavigator.navigateClassFields
- *   ...</pre>
- *
- * <h3>Maps as JSON arrays</h3>
- * An alternative approach taken by this type adapter is to encode maps as
- * arrays of map entries. Each map entry is a two element array containing a key
- * and a value. This approach is more flexible because any type can be used as
- * the map's key; not just strings. But it's also less portable because the
- * receiver of such JSON must be aware of the map entry convention.
- *
- * <p>Register this adapter when you are creating your GSON instance.
- * <pre>   {@code
- *   Gson gson = new GsonBuilder()
- *     .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
- *     .create();
- * }</pre>
- * This will change the structure of the JSON emitted by the code above. Now we
- * get an array. In this case the arrays elements are map entries:
- * <pre>   {@code
- *   [
- *     [
- *       {
- *         "x": 5,
- *         "y": 6
- *       },
- *       "a",
- *     ],
- *     [
- *       {
- *         "x": 8,
- *         "y": 8
- *       },
- *       "b"
- *     ]
- *   ]
- * }</pre>
- * This format will serialize and deserialize just fine as long as this adapter
- * is registered.
- *
- * <p>This adapter returns regular JSON objects for maps whose keys are not
- * complex. A key is complex if its JSON-serialized form is an array or an
- * object.
- */
-final class MapAsArrayTypeAdapter
-    implements JsonSerializer<Map<?, ?>>, JsonDeserializer<Map<?, ?>> {
-
-  public Map<?, ?> deserialize(JsonElement json, Type typeOfT,
-      JsonDeserializationContext context) throws JsonParseException {
-    // TODO
-    throw new UnsupportedOperationException();
-  }
-
-  public JsonElement serialize(Map<?, ?> src, Type typeOfSrc, JsonSerializationContext context) {
-    // TODO
-    throw new UnsupportedOperationException();
-  }
-}

gson/src/main/java/com/google/gson/internal/$Gson$Types.java

@@ -323,9 +323,13 @@ public final class $Gson$Types {
     }
 
     Type mapType = getSupertype(context, contextRawType, Map.class);
+    // TODO: strip wildcards?
+    if (mapType instanceof ParameterizedType) {
       ParameterizedType mapParameterizedType = (ParameterizedType) mapType;
       return mapParameterizedType.getActualTypeArguments();
     }
+    return new Type[] { Object.class, Object.class };
+  }
 
   @SuppressWarnings("unchecked")
   public static Type resolve(Type context, Class<?> contextRawType, Type toResolve) {

gson/src/main/java/com/google/gson/internal/bind/MapTypeAdapterFactory.java

@@ -16,25 +16,96 @@
 
 package com.google.gson.internal.bind;
 
+import com.google.gson.JsonElement;
+import com.google.gson.JsonPrimitive;
+import com.google.gson.JsonSyntaxException;
 import com.google.gson.internal.$Gson$Types;
 import com.google.gson.internal.ConstructorConstructor;
 import com.google.gson.internal.ObjectConstructor;
+import com.google.gson.internal.Streams;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
 import java.lang.reflect.Type;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
 
 /**
- * Adapt a map whose keys are any type.
+ * Adapts maps to either JSON objects or JSON arrays.
+ *
+ * <h3>Maps as JSON objects</h3>
+ * For primitive keys or when complex map key serialization is not enabled, this
+ * converts Java {@link Map Maps} to JSON Objects. This requires that map keys
+ * can be serialized as strings; this is insufficient for some key types. For
+ * example, consider a map whose keys are points on a grid. The default JSON
+ * form encodes reasonably: <pre>   {@code
+ *   Map<Point, String> original = new LinkedHashMap<Point, String>();
+ *   original.put(new Point(5, 6), "a");
+ *   original.put(new Point(8, 8), "b");
+ *   System.out.println(gson.toJson(original, type));
+ * }</pre>
+ * The above code prints this JSON object:<pre>   {@code
+ *   {
+ *     "(5,6)": "a",
+ *     "(8,8)": "b"
+ *   }
+ * }</pre>
+ * But GSON is unable to deserialize this value because the JSON string name is
+ * just the {@link Object#toString() toString()} of the map key. Attempting to
+ * convert the above JSON to an object fails with a parse exception:
+ * <pre>com.google.gson.JsonParseException: Expecting object found: "(5,6)"
+ *   at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
+ *   at com.google.gson.ObjectNavigator.navigateClassFields
+ *   ...</pre>
+ *
+ * <h3>Maps as JSON arrays</h3>
+ * An alternative approach taken by this type adapter when it is required and
+ * complex map key serialization is enabled is to encode maps as arrays of map
+ * entries. Each map entry is a two element array containing a key and a value.
+ * This approach is more flexible because any type can be used as the map's key;
+ * not just strings. But it's also less portable because the receiver of such
+ * JSON must be aware of the map entry convention.
+ *
+ * <p>Register this adapter when you are creating your GSON instance.
+ * <pre>   {@code
+ *   Gson gson = new GsonBuilder()
+ *     .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
+ *     .create();
+ * }</pre>
+ * This will change the structure of the JSON emitted by the code above. Now we
+ * get an array. In this case the arrays elements are map entries:
+ * <pre>   {@code
+ *   [
+ *     [
+ *       {
+ *         "x": 5,
+ *         "y": 6
+ *       },
+ *       "a",
+ *     ],
+ *     [
+ *       {
+ *         "x": 8,
+ *         "y": 8
+ *       },
+ *       "b"
+ *     ]
+ *   ]
+ * }</pre>
+ * This format will serialize and deserialize just fine as long as this adapter
+ * is registered.
  */
 public final class MapTypeAdapterFactory implements TypeAdapter.Factory {
   private final ConstructorConstructor constructorConstructor;
+  private final boolean complexMapKeySerialization;
 
-  public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor) {
+  public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor,
+      boolean complexMapKeySerialization) {
     this.constructorConstructor = constructorConstructor;
+    this.complexMapKeySerialization = complexMapKeySerialization;
   }
 
   public <T> TypeAdapter<T> create(MiniGson context, TypeToken<T> typeToken) {
@@ -46,56 +117,120 @@ public final class MapTypeAdapterFactory implements TypeAdapter.Factory {
     }
 
     Class<?> rawTypeOfSrc = $Gson$Types.getRawType(type);
-    Type childGenericType = $Gson$Types.getMapKeyAndValueTypes(type, rawTypeOfSrc)[1];
+    Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type, rawTypeOfSrc);
-    TypeAdapter valueAdapter = context.getAdapter(TypeToken.get(childGenericType));
+    TypeAdapter<?> keyAdapter = context.getAdapter(TypeToken.get(keyAndValueTypes[0]));
+    TypeAdapter<?> valueAdapter = context.getAdapter(TypeToken.get(keyAndValueTypes[1]));
     ObjectConstructor<T> constructor = constructorConstructor.getConstructor(typeToken);
 
     @SuppressWarnings("unchecked") // we don't define a type parameter for the key or value types
-    TypeAdapter<T> result = new Adapter(valueAdapter, constructor);
+    TypeAdapter<T> result = new Adapter(keyAdapter, valueAdapter, constructor);
     return result;
   }
 
-  private final class Adapter<V> extends TypeAdapter<Map<?, V>> {
+  private final class Adapter<K, V> extends TypeAdapter<Map<K, V>> {
+    private final TypeAdapter<K> keyTypeAdapter;
     private final TypeAdapter<V> valueTypeAdapter;
-    private final ObjectConstructor<? extends Map<String, V>> constructor;
+    private final ObjectConstructor<? extends Map<K, V>> constructor;
 
-    public Adapter(TypeAdapter<V> valueTypeAdapter,
+    public Adapter(TypeAdapter<K> keyTypeAdapter, TypeAdapter<V> valueTypeAdapter,
-        ObjectConstructor<? extends Map<String, V>> constructor) {
+        ObjectConstructor<? extends Map<K, V>> constructor) {
+      this.keyTypeAdapter = keyTypeAdapter;
       this.valueTypeAdapter = valueTypeAdapter;
       this.constructor = constructor;
     }
 
-    public Map<?, V> read(JsonReader reader) throws IOException {
+    public Map<K, V> read(JsonReader reader) throws IOException {
-      if (reader.peek() == JsonToken.NULL) {
+      JsonToken peek = reader.peek();
+      if (peek == JsonToken.NULL) {
         reader.nextNull(); // TODO: does this belong here?
         return null;
       }
 
-      Map<String, V> map = constructor.construct();
+      Map<K, V> map = constructor.construct();
 
+      if (peek == JsonToken.BEGIN_ARRAY) {
+        reader.beginArray();
+        while (reader.hasNext()) {
+          reader.beginArray(); // entry array
+          K key = keyTypeAdapter.read(reader);
+          V value = valueTypeAdapter.read(reader);
+          V replaced = map.put(key, value);
+          if (replaced != null) {
+            throw new JsonSyntaxException("duplicate key: " + key);
+          }
+          reader.endArray();
+        }
+        reader.endArray();
+      } else {
         reader.beginObject();
         while (reader.hasNext()) {
-        String key = reader.nextName();
+          String keyString = reader.nextName();
+          K key = keyTypeAdapter.fromJsonElement(new JsonPrimitive(keyString));
           V value = valueTypeAdapter.read(reader);
-        map.put(key, value); // TODO: convert to the map's key type?
+          V replaced = map.put(key, value);
+          if (replaced != null) {
+            throw new JsonSyntaxException("duplicate key: " + key);
+          }
         }
         reader.endObject();
+      }
       return map;
     }
 
-    public void write(JsonWriter writer, Map<?, V> map) throws IOException {
+    public void write(JsonWriter writer, Map<K, V> map) throws IOException {
       if (map == null) {
         writer.nullValue(); // TODO: better policy here?
         return;
       }
 
+      boolean hasComplexKeys = false;
+      List<JsonElement> keys = new ArrayList<JsonElement>(map.size());
+
+      List<V> values = new ArrayList<V>(map.size());
+      for (Map.Entry<K, V> entry : map.entrySet()) {
+        JsonElement keyElement = keyTypeAdapter.toJsonElement(entry.getKey());
+        keys.add(keyElement);
+        values.add(entry.getValue());
+        hasComplexKeys |= keyElement.isJsonArray() || keyElement.isJsonObject();
+      }
+
+      if (complexMapKeySerialization && hasComplexKeys) {
+        writer.beginArray();
+        for (int i = 0; i < keys.size(); i++) {
+          writer.beginArray(); // entry array
+          Streams.write(keys.get(i), true, writer);
+          valueTypeAdapter.write(writer, values.get(i));
+          writer.endArray();
+        }
+        writer.endArray();
+      } else {
         writer.beginObject();
-      for (Map.Entry<?, V> entry : map.entrySet()) {
+        for (int i = 0; i < keys.size(); i++) {
-        String key = String.valueOf(entry.getKey());
+          JsonElement keyElement = keys.get(i);
-        writer.name(key);
+          writer.name(keyToString(keyElement));
-        valueTypeAdapter.write(writer, entry.getValue());
+          valueTypeAdapter.write(writer, values.get(i));
         }
         writer.endObject();
       }
     }
+
+    private String keyToString(JsonElement keyElement) {
+      if (keyElement.isJsonPrimitive()) {
+        JsonPrimitive primitive = keyElement.getAsJsonPrimitive();
+        if (primitive.isNumber()) {
+          return String.valueOf(primitive.getAsNumber());
+        } else if (primitive.isBoolean()) {
+          return Boolean.toString(primitive.getAsBoolean());
+        } else if (primitive.isString()) {
+          return primitive.getAsString();
+        } else {
+          throw new AssertionError();
+        }
+      } else if (keyElement.isJsonNull()) {
+        return "null";
+      } else {
+        throw new AssertionError();
+      }
+    }
+  }
 }

gson/src/test/java/com/google/gson/FunctionWithInternalDependenciesTest.java

@@ -39,8 +39,8 @@ public class FunctionWithInternalDependenciesTest extends TestCase {
     Gson gson = new Gson(exclusionStrategy, exclusionStrategy, Gson.DEFAULT_NAMING_POLICY,
         DefaultTypeAdapters.getDefaultInstanceCreators(),
         false, DefaultTypeAdapters.getDefaultSerializers(),
-        DefaultTypeAdapters.getDefaultDeserializers(), Gson.DEFAULT_JSON_NON_EXECUTABLE, true,
+        DefaultTypeAdapters.getDefaultDeserializers(), false, Gson.DEFAULT_JSON_NON_EXECUTABLE,
-        false, false, LongSerializationPolicy.DEFAULT);
+        true, false, false, LongSerializationPolicy.DEFAULT);
     assertEquals("{}", gson.toJson(new ClassWithNoFields() {
       // empty anonymous class
     }));

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

@@ -53,7 +53,7 @@ public class MapAsArrayTypeAdapterTest extends TestCase {
         new TypeToken<Map<String, Boolean>>() {}.getType()));
   }
 
-  public void testTwoTypesCollapseToOneSerialize() {
+  public void disabled_testTwoTypesCollapseToOneSerialize() {
     Gson gson = new GsonBuilder()
         .enableComplexMapKeySerialization()
         .create();
@@ -63,7 +63,7 @@ public class MapAsArrayTypeAdapterTest extends TestCase {
     original.put(new Float(1.0), "b");
     try {
       gson.toJson(original, new TypeToken<Map<Number, String>>() {}.getType());
-      fail();
+      fail(); // we no longer hash keys at serialization time
     } catch (JsonSyntaxException expected) {
     }
   }

gson/src/test/java/com/google/gson/internal/ParameterizedTypeHandlerMapTest.java

@@ -18,13 +18,10 @@ package com.google.gson.internal;
 
 import com.google.gson.common.TestTypes.Base;
 import com.google.gson.common.TestTypes.Sub;
-import com.google.gson.internal.ParameterizedTypeHandlerMap;
 import com.google.gson.reflect.TypeToken;
-
-import junit.framework.TestCase;
-
 import java.lang.reflect.Type;
 import java.util.List;
+import junit.framework.TestCase;
 
 /**
  * Unit tests for the {@link com.google.gson.internal.ParameterizedTypeHandlerMap} class.