JsonDeserializationVisitor.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;

import com.smartandroid.sa.json.internal.$Gson$Preconditions;

/**
 * Abstract data value container for the {@link ObjectNavigator.Visitor}
 * implementations. This class exposes the {@link #getTarget()} method which
 * returns the class that was visited by this object.
 * 
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
abstract class JsonDeserializationVisitor<T> implements ObjectNavigator.Visitor {

	protected final ObjectNavigator objectNavigator;
	protected final FieldNamingStrategy2 fieldNamingPolicy;
	protected final ObjectConstructor objectConstructor;
	protected final ParameterizedTypeHandlerMap<JsonDeserializer<?>> deserializers;
	protected T target;
	protected final JsonElement json;
	protected final Type targetType;
	protected final JsonDeserializationContext context;
	protected boolean constructed;

	JsonDeserializationVisitor(JsonElement json, Type targetType,
			ObjectNavigator objectNavigator,
			FieldNamingStrategy2 fieldNamingPolicy,
			ObjectConstructor objectConstructor,
			ParameterizedTypeHandlerMap<JsonDeserializer<?>> deserializers,
			JsonDeserializationContext context) {
		this.targetType = targetType;
		this.objectNavigator = objectNavigator;
		this.fieldNamingPolicy = fieldNamingPolicy;
		this.objectConstructor = objectConstructor;
		this.deserializers = deserializers;
		this.json = $Gson$Preconditions.checkNotNull(json);
		this.context = context;
		this.constructed = false;
	}

	public T getTarget() {
		if (!constructed) {
			target = constructTarget();
			constructed = true;
		}
		return target;
	}

	protected abstract T constructTarget();

	public void start(ObjectTypePair node) {
	}

	public void end(ObjectTypePair node) {
	}

	@SuppressWarnings("unchecked")
	public final boolean visitUsingCustomHandler(ObjectTypePair objTypePair) {
		Pair<JsonDeserializer<?>, ObjectTypePair> pair = objTypePair
				.getMatchingHandler(deserializers);
		if (pair == null) {
			return false;
		}
		Object value = invokeCustomDeserializer(json, pair);
		target = (T) value;
		constructed = true;
		return true;
	}

	protected Object invokeCustomDeserializer(JsonElement element,
			Pair<JsonDeserializer<?>, ObjectTypePair> pair) {
		if (element == null || element.isJsonNull()) {
			return null;
		}
		Type objType = pair.second.type;
		return (pair.first).deserialize(element, objType, context);
	}

	final Object visitChildAsObject(Type childType, JsonElement jsonChild) {
		JsonDeserializationVisitor<?> childVisitor = new JsonObjectDeserializationVisitor<Object>(
				jsonChild, childType, objectNavigator, fieldNamingPolicy,
				objectConstructor, deserializers, context);
		return visitChild(childType, childVisitor);
	}

	final Object visitChildAsArray(Type childType, JsonArray jsonChild) {
		JsonDeserializationVisitor<?> childVisitor = new JsonArrayDeserializationVisitor<Object>(
				jsonChild.getAsJsonArray(), childType, objectNavigator,
				fieldNamingPolicy, objectConstructor, deserializers, context);
		return visitChild(childType, childVisitor);
	}

	private Object visitChild(Type type,
			JsonDeserializationVisitor<?> childVisitor) {
		objectNavigator.accept(new ObjectTypePair(null, type, false, false),
				childVisitor);
		// the underlying object may have changed during the construction phase
		// This happens primarily because of custom deserializers
		return childVisitor.getTarget();
	}
}