com.google.gson.internal.bind.MapTypeAdapterFactory Maven / Gradle / Ivy
/*
* Copyright (C) 2011 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.internal.bind;
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSyntaxException;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.internal.$Gson$Types;
import com.google.gson.internal.ConstructorConstructor;
import com.google.gson.internal.JsonReaderInternalAccess;
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;
/**
* Adapts maps to either JSON objects or JSON arrays.
*
* Maps as JSON objects
* 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: {@code
* Map original = new LinkedHashMap();
* original.put(new Point(5, 6), "a");
* original.put(new Point(8, 8), "b");
* System.out.println(gson.toJson(original, type));
* }
* The above code prints this JSON object: {@code
* {
* "(5,6)": "a",
* "(8,8)": "b"
* }
* }
* 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:
* com.google.gson.JsonParseException: Expecting object found: "(5,6)"
* at com.google.gson.JsonObjectDeserializationVisitor.visitFieldUsingCustomHandler
* at com.google.gson.ObjectNavigator.navigateClassFields
* ...
*
* Maps as JSON arrays
* 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.
*
* Register this adapter when you are creating your GSON instance.
*
{@code
* Gson gson = new GsonBuilder()
* .registerTypeAdapter(Map.class, new MapAsArrayTypeAdapter())
* .create();
* }
* 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:
* {@code
* [
* [
* {
* "x": 5,
* "y": 6
* },
* "a",
* ],
* [
* {
* "x": 8,
* "y": 8
* },
* "b"
* ]
* ]
* }
* This format will serialize and deserialize just fine as long as this adapter
* is registered.
*/
public final class MapTypeAdapterFactory implements TypeAdapterFactory {
private final ConstructorConstructor constructorConstructor;
final boolean complexMapKeySerialization;
public MapTypeAdapterFactory(ConstructorConstructor constructorConstructor,
boolean complexMapKeySerialization) {
this.constructorConstructor = constructorConstructor;
this.complexMapKeySerialization = complexMapKeySerialization;
}
@Override public TypeAdapter create(Gson gson, TypeToken typeToken) {
Type type = typeToken.getType();
Class rawType = typeToken.getRawType();
if (!Map.class.isAssignableFrom(rawType)) {
return null;
}
Class rawTypeOfSrc = $Gson$Types.getRawType(type);
Type[] keyAndValueTypes = $Gson$Types.getMapKeyAndValueTypes(type, rawTypeOfSrc);
TypeAdapter keyAdapter = getKeyAdapter(gson, keyAndValueTypes[0]);
TypeAdapter valueAdapter = gson.getAdapter(TypeToken.get(keyAndValueTypes[1]));
ObjectConstructor constructor = constructorConstructor.get(typeToken);
@SuppressWarnings({"unchecked", "rawtypes"})
// we don't define a type parameter for the key or value types
TypeAdapter result = new Adapter(gson, keyAndValueTypes[0], keyAdapter,
keyAndValueTypes[1], valueAdapter, constructor);
return result;
}
/**
* Returns a type adapter that writes the value as a string.
*/
private TypeAdapter getKeyAdapter(Gson context, Type keyType) {
return (keyType == boolean.class || keyType == Boolean.class)
? TypeAdapters.BOOLEAN_AS_STRING
: context.getAdapter(TypeToken.get(keyType));
}
private final class Adapter extends TypeAdapter> {
private final TypeAdapter keyTypeAdapter;
private final TypeAdapter valueTypeAdapter;
private final ObjectConstructor> constructor;
public Adapter(Gson context, Type keyType, TypeAdapter keyTypeAdapter,
Type valueType, TypeAdapter valueTypeAdapter,
ObjectConstructor> constructor) {
this.keyTypeAdapter =
new TypeAdapterRuntimeTypeWrapper(context, keyTypeAdapter, keyType);
this.valueTypeAdapter =
new TypeAdapterRuntimeTypeWrapper(context, valueTypeAdapter, valueType);
this.constructor = constructor;
}
@Override public Map read(JsonReader in) throws IOException {
JsonToken peek = in.peek();
if (peek == JsonToken.NULL) {
in.nextNull();
return null;
}
Map map = constructor.construct();
if (peek == JsonToken.BEGIN_ARRAY) {
in.beginArray();
while (in.hasNext()) {
in.beginArray(); // entry array
K key = keyTypeAdapter.read(in);
V value = valueTypeAdapter.read(in);
V replaced = map.put(key, value);
if (replaced != null) {
throw new JsonSyntaxException("duplicate key: " + key);
}
in.endArray();
}
in.endArray();
} else {
in.beginObject();
while (in.hasNext()) {
JsonReaderInternalAccess.INSTANCE.promoteNameToValue(in);
K key = keyTypeAdapter.read(in);
V value = valueTypeAdapter.read(in);
V replaced = map.put(key, value);
if (replaced != null) {
throw new JsonSyntaxException("duplicate key: " + key);
}
}
in.endObject();
}
return map;
}
@Override public void write(JsonWriter out, Map map) throws IOException {
if (map == null) {
out.nullValue();
return;
}
if (!complexMapKeySerialization) {
out.beginObject();
for (Map.Entry entry : map.entrySet()) {
out.name(String.valueOf(entry.getKey()));
valueTypeAdapter.write(out, entry.getValue());
}
out.endObject();
return;
}
boolean hasComplexKeys = false;
List keys = new ArrayList(map.size());
List values = new ArrayList(map.size());
for (Map.Entry entry : map.entrySet()) {
JsonElement keyElement = keyTypeAdapter.toJsonTree(entry.getKey());
keys.add(keyElement);
values.add(entry.getValue());
hasComplexKeys |= keyElement.isJsonArray() || keyElement.isJsonObject();
}
if (hasComplexKeys) {
out.beginArray();
for (int i = 0, size = keys.size(); i < size; i++) {
out.beginArray(); // entry array
Streams.write(keys.get(i), out);
valueTypeAdapter.write(out, values.get(i));
out.endArray();
}
out.endArray();
} else {
out.beginObject();
for (int i = 0, size = keys.size(); i < size; i++) {
JsonElement keyElement = keys.get(i);
out.name(keyToString(keyElement));
valueTypeAdapter.write(out, values.get(i));
}
out.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();
}
}
}
}