JsonDeserializationContext.java

/*
 * 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.smartandroid.sa.json;

import java.lang.reflect.Type;

/**
 * Context for deserialization that is passed to a custom deserializer during
 * invocation of its
 * {@link JsonDeserializer#deserialize(JsonElement, Type, JsonDeserializationContext)}
 * method.
 * 
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
public class JsonDeserializationContext {
	private final ObjectNavigator objectNavigator;
	private final FieldNamingStrategy2 fieldNamingPolicy;
	private final ParameterizedTypeHandlerMap<JsonDeserializer<?>> deserializers;
	private final MappedObjectConstructor objectConstructor;

	JsonDeserializationContext(ObjectNavigator objectNavigator,
			FieldNamingStrategy2 fieldNamingPolicy,
			ParameterizedTypeHandlerMap<JsonDeserializer<?>> deserializers,
			MappedObjectConstructor objectConstructor) {
		this.objectNavigator = objectNavigator;
		this.fieldNamingPolicy = fieldNamingPolicy;
		this.deserializers = deserializers;
		this.objectConstructor = objectConstructor;
	}

	JsonDeserializationContext() {
		this(null, null, null, null);
	}

	@SuppressWarnings("unchecked")
	public <T> T construct(Type type) {
		Object instance = objectConstructor.construct(type);
		return (T) instance;
	}

	public Object constructArray(Type type, int length) {
		return objectConstructor.constructArray(type, length);
	}

	private <T> T fromJsonArray(Type arrayType, JsonArray jsonArray,
			JsonDeserializationContext context, boolean systemOnly)
			throws JsonParseException {
		JsonArrayDeserializationVisitor<T> visitor = new JsonArrayDeserializationVisitor<T>(
				jsonArray, arrayType, objectNavigator, fieldNamingPolicy,
				objectConstructor, deserializers, context);
		objectNavigator.accept(new ObjectTypePair(null, arrayType, true,
				systemOnly), visitor);
		return visitor.getTarget();
	}

	private <T> T fromJsonObject(Type typeOfT, JsonObject jsonObject,
			JsonDeserializationContext context, boolean systemOnly)
			throws JsonParseException {
		JsonObjectDeserializationVisitor<T> visitor = new JsonObjectDeserializationVisitor<T>(
				jsonObject, typeOfT, objectNavigator, fieldNamingPolicy,
				objectConstructor, deserializers, context);
		objectNavigator.accept(new ObjectTypePair(null, typeOfT, true,
				systemOnly), visitor);
		return visitor.getTarget();
	}

	@SuppressWarnings("unchecked")
	private <T> T fromJsonPrimitive(Type typeOfT, JsonPrimitive json,
			JsonDeserializationContext context, boolean systemOnly)
			throws JsonParseException {
		JsonObjectDeserializationVisitor<T> visitor = new JsonObjectDeserializationVisitor<T>(
				json, typeOfT, objectNavigator, fieldNamingPolicy,
				objectConstructor, deserializers, context);
		objectNavigator.accept(new ObjectTypePair(json.getAsObject(), typeOfT,
				true, systemOnly), visitor);
		Object target = visitor.getTarget();
		return (T) target;
	}

	/**
	 * Invokes default deserialization on the specified object. It should never
	 * be invoked on the element received as a parameter of the
	 * {@link JsonDeserializer#deserialize(JsonElement, Type, JsonDeserializationContext)}
	 * method. Doing so will result in an infinite loop since Gson will in-turn
	 * call the custom deserializer again.
	 * 
	 * @param json
	 *            the parse tree.
	 * @param typeOfT
	 *            type of the expected return value.
	 * @param <T>
	 *            The type of the deserialized object.
	 * @return An object of type typeOfT.
	 * @throws JsonParseException
	 *             if the parse tree does not contain expected data.
	 */
	@SuppressWarnings("unchecked")
	public <T> T deserialize(JsonElement json, Type typeOfT)
			throws JsonParseException {
		if (json == null || json.isJsonNull()) {
			return null;
		} else if (json.isJsonArray()) {
			Object array = fromJsonArray(typeOfT, json.getAsJsonArray(), this,
					false);
			return (T) array;
		} else if (json.isJsonObject()) {
			Object object = fromJsonObject(typeOfT, json.getAsJsonObject(),
					this, false);
			return (T) object;
		} else if (json.isJsonPrimitive()) {
			Object primitive = fromJsonPrimitive(typeOfT,
					json.getAsJsonPrimitive(), this, false);
			return (T) primitive;
		} else {
			throw new JsonParseException("Failed parsing JSON source: " + json
					+ " to Json");
		}
	}

	@SuppressWarnings("unchecked")
	public <T> T deserializeDefault(JsonElement json, Type typeOfT)
			throws JsonParseException {
		if (json == null || json.isJsonNull()) {
			return null;
		} else if (json.isJsonArray()) {
			Object array = fromJsonArray(typeOfT, json.getAsJsonArray(), this,
					true);
			return (T) array;
		} else if (json.isJsonObject()) {
			Object object = fromJsonObject(typeOfT, json.getAsJsonObject(),
					this, true);
			return (T) object;
		} else if (json.isJsonPrimitive()) {
			Object primitive = fromJsonPrimitive(typeOfT,
					json.getAsJsonPrimitive(), this, true);
			return (T) primitive;
		} else {
			throw new JsonParseException("Failed parsing JSON source: " + json
					+ " to Json");
		}
	}
}