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

   1 /*
   2  * Copyright (C) 2011 Google Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *      http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 package com.google.gson.internal.bind;
  18
  19 import com.google.gson.Gson;
  20 import com.google.gson.JsonElement;
  21 import com.google.gson.JsonPrimitive;
  22 import com.google.gson.JsonSyntaxException;
  23 import com.google.gson.TypeAdapter;
  24 import com.google.gson.TypeAdapterFactory;
  25 import com.google.gson.internal.$Gson$Types;
  26 import com.google.gson.internal.ConstructorConstructor;
  27 import com.google.gson.internal.JsonReaderInternalAccess;
  28 import com.google.gson.internal.ObjectConstructor;
  29 import com.google.gson.internal.Streams;
  30 import com.google.gson.reflect.TypeToken;
  31 import com.google.gson.stream.JsonReader;
  32 import com.google.gson.stream.JsonToken;
  33 import com.google.gson.stream.JsonWriter;
  34 import java.io.IOException;
  35 import java.lang.reflect.Type;
  36 import java.util.ArrayList;
  37 import java.util.List;
  38 import java.util.Map;
  39
  40 /**
  41  * Adapts maps to either JSON objects or JSON arrays.
  42  *
  43  * <h3>Maps as JSON objects</h3>
  44  * For primitive keys or when complex map key serialization is not enabled, this
  45  * converts Java {@link Map Maps} to JSON Objects. This requires that map keys
  46  * can be serialized as strings; this is insufficient for some key types. For
  47  * example, consider a map whose keys are points on a grid. The default JSON
  48  * form encodes reasonably: <pre>   {@code
  49  *   Map<Point, String> original = new LinkedHashMap<Point, String>();
  50  *   original.put(new Point(5, 6), "a");
  51  *   original.put(new Point(8, 8), "b");
  52  *   System.out.println(gson.toJson(original, type));
  53  * }</pre>
  54  * The above code prints this JSON object:<pre>   {@code
  55  *   {
  56  *     "(5,6)": "a",
  57  *     "(8,8)": "b"
  58  *   }
  59  * }</pre>
  60  * But GSON is unable to deserialize this value because the JSON string name is
  61  * just the {@link Object#toString() toString()} of the map key. Attempting to
  62  * convert the above JSON to an object fails with a parse exception:
  63  * <pre>com.google.gson.JsonParseException: Expecting object found: "(5,6)"
  64  *   at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
  65  *   at com.google.gson.ObjectNavigator.navigateClassFields
  66  *   ...</pre>
  67  *
  68  * <h3>Maps as JSON arrays</h3>
  69  * An alternative approach taken by this type adapter when it is required and
  70  * complex map key serialization is enabled is to encode maps as arrays of map
  71  * entries. Each map entry is a two element array containing a key and a value.
  72  * This approach is more flexible because any type can be used as the map's key;
  73  * not just strings. But it's also less portable because the receiver of such
  74  * JSON must be aware of the map entry convention.
  75  *
  76  * <p>Register this adapter when you are creating your GSON instance.
  77  * <pre>   {@code
  78  *   Gson gson = new GsonBuilder()
  79  *     .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
  80  *     .create();
  81  * }</pre>
  82  * This will change the structure of the JSON emitted by the code above. Now we
  83  * get an array. In this case the arrays elements are map entries:
  84  * <pre>   {@code
  85  *   [
  86  *     [
  87  *       {
  88  *         "x": 5,
  89  *         "y": 6
  90  *       },
  91  *       "a",
  92  *     ],
  93  *     [
  94  *       {
  95  *         "x": 8,
  96  *         "y": 8
  97  *       },
  98  *       "b"
  99  *     ]
 100  *   ]
 101  * }</pre>
 102  * This format will serialize and deserialize just fine as long as this adapter
 103  * is registered.
 104  */
 105 public final class MapTypeAdapterFactory implements TypeAdapterFactory {
 106   private final ConstructorConstructor constructorConstructor;
 107   private final boolean complexMapKeySerialization;
 108
 109   public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor,
 110       boolean complexMapKeySerialization) {
 111     this.constructorConstructor = constructorConstructor;
 112     this.complexMapKeySerialization = complexMapKeySerialization;
 113   }
 114
 115   public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {
 116     Type type = typeToken.getType();
 117
 118     Class<? super T> rawType = typeToken.getRawType();
 119     if (!Map.class.isAssignableFrom(rawType)) {
 120       return null;
 121     }
 122
 123     Class<?> rawTypeOfSrc = $Gson$Types.getRawType(type);
 124     Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type, rawTypeOfSrc);
 125     TypeAdapter<?> keyAdapter = getKeyAdapter(gson, keyAndValueTypes[0]);
 126     TypeAdapter<?> valueAdapter = gson.getAdapter(TypeToken.get(keyAndValueTypes[1]));
 127     ObjectConstructor<T> constructor = constructorConstructor.get(typeToken);
 128
 129     @SuppressWarnings({"unchecked", "rawtypes"})
 130     // we don't define a type parameter for the key or value types
 131     TypeAdapter<T> result = new Adapter(gson, keyAndValueTypes[0], keyAdapter,
 132         keyAndValueTypes[1], valueAdapter, constructor);
 133     return result;
 134   }
 135
 136   /**
 137    * Returns a type adapter that writes the value as a string.
 138    */
 139   private TypeAdapter<?> getKeyAdapter(Gson context, Type keyType) {
 140     return (keyType == boolean.class || keyType == Boolean.class)
 141         ? TypeAdapters.BOOLEAN_AS_STRING
 142         : context.getAdapter(TypeToken.get(keyType));
 143   }
 144
 145   private final class Adapter<K, V> extends TypeAdapter<Map<K, V>> {
 146     private final TypeAdapter<K> keyTypeAdapter;
 147     private final TypeAdapter<V> valueTypeAdapter;
 148     private final ObjectConstructor<? extends Map<K, V>> constructor;
 149
 150     public Adapter(Gson context, Type keyType, TypeAdapter<K> keyTypeAdapter,
 151         Type valueType, TypeAdapter<V> valueTypeAdapter,
 152         ObjectConstructor<? extends Map<K, V>> constructor) {
 153       this.keyTypeAdapter =
 154         new TypeAdapterRuntimeTypeWrapper<K>(context, keyTypeAdapter, keyType);
 155       this.valueTypeAdapter =
 156         new TypeAdapterRuntimeTypeWrapper<V>(context, valueTypeAdapter, valueType);
 157       this.constructor = constructor;
 158     }
 159
 160     public Map<K, V> read(JsonReader in) throws IOException {
 161       JsonToken peek = in.peek();
 162       if (peek == JsonToken.NULL) {
 163         in.nextNull();
 164         return null;
 165       }
 166
 167       Map<K, V> map = constructor.construct();
 168
 169       if (peek == JsonToken.BEGIN_ARRAY) {
 170         in.beginArray();
 171         while (in.hasNext()) {
 172           in.beginArray(); // entry array
 173           K key = keyTypeAdapter.read(in);
 174           V value = valueTypeAdapter.read(in);
 175           V replaced = map.put(key, value);
 176           if (replaced != null) {
 177             throw new JsonSyntaxException("duplicate key: " + key);
 178           }
 179           in.endArray();
 180         }
 181         in.endArray();
 182       } else {
 183         in.beginObject();
 184         while (in.hasNext()) {
 185           JsonReaderInternalAccess.INSTANCE.promoteNameToValue(in);
 186           K key = keyTypeAdapter.read(in);
 187           V value = valueTypeAdapter.read(in);
 188           V replaced = map.put(key, value);
 189           if (replaced != null) {
 190             throw new JsonSyntaxException("duplicate key: " + key);
 191           }
 192         }
 193         in.endObject();
 194       }
 195       return map;
 196     }
 197
 198     public void write(JsonWriter out, Map<K, V> map) throws IOException {
 199       if (map == null) {
 200         out.nullValue();
 201         return;
 202       }
 203
 204       if (!complexMapKeySerialization) {
 205         out.beginObject();
 206         for (Map.Entry<K, V> entry : map.entrySet()) {
 207           out.name(String.valueOf(entry.getKey()));
 208           valueTypeAdapter.write(out, entry.getValue());
 209         }
 210         out.endObject();
 211         return;
 212       }
 213
 214       boolean hasComplexKeys = false;
 215       List<JsonElement> keys = new ArrayList<JsonElement>(map.size());
 216
 217       List<V> values = new ArrayList<V>(map.size());
 218       for (Map.Entry<K, V> entry : map.entrySet()) {
 219         JsonElement keyElement = keyTypeAdapter.toJsonTree(entry.getKey());
 220         keys.add(keyElement);
 221         values.add(entry.getValue());
 222         hasComplexKeys |= keyElement.isJsonArray() || keyElement.isJsonObject();
 223       }
 224
 225       if (hasComplexKeys) {
 226         out.beginArray();
 227         for (int i = 0; i < keys.size(); i++) {
 228           out.beginArray(); // entry array
 229           Streams.write(keys.get(i), out);
 230           valueTypeAdapter.write(out, values.get(i));
 231           out.endArray();
 232         }
 233         out.endArray();
 234       } else {
 235         out.beginObject();
 236         for (int i = 0; i < keys.size(); i++) {
 237           JsonElement keyElement = keys.get(i);
 238           out.name(keyToString(keyElement));
 239           valueTypeAdapter.write(out, values.get(i));
 240         }
 241         out.endObject();
 242       }
 243     }
 244
 245     private String keyToString(JsonElement keyElement) {
 246       if (keyElement.isJsonPrimitive()) {
 247         JsonPrimitive primitive = keyElement.getAsJsonPrimitive();
 248         if (primitive.isNumber()) {
 249           return String.valueOf(primitive.getAsNumber());
 250         } else if (primitive.isBoolean()) {
 251           return Boolean.toString(primitive.getAsBoolean());
 252         } else if (primitive.isString()) {
 253           return primitive.getAsString();
 254         } else {
 255           throw new AssertionError();
 256         }
 257       } else if (keyElement.isJsonNull()) {
 258         return "null";
 259       } else {
 260         throw new AssertionError();
 261       }
 262     }
 263   }
 264 }