JsonSerializationVisitor.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.Array;
import java.lang.reflect.Type;

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

/**
 * A visitor that adds JSON elements corresponding to each field of an object
 * 
 * @author Inderjeet Singh
 * @author Joel Leitch
 */
final class JsonSerializationVisitor implements ObjectNavigator.Visitor {

	private final ObjectNavigator objectNavigator;
	private final FieldNamingStrategy2 fieldNamingPolicy;
	private final ParameterizedTypeHandlerMap<JsonSerializer<?>> serializers;
	private final boolean serializeNulls;
	private final JsonSerializationContext context;
	private final MemoryRefStack ancestors;
	private JsonElement root;

	JsonSerializationVisitor(ObjectNavigator objectNavigator,
			FieldNamingStrategy2 fieldNamingPolicy, boolean serializeNulls,
			ParameterizedTypeHandlerMap<JsonSerializer<?>> serializers,
			JsonSerializationContext context, MemoryRefStack ancestors) {
		this.objectNavigator = objectNavigator;
		this.fieldNamingPolicy = fieldNamingPolicy;
		this.serializeNulls = serializeNulls;
		this.serializers = serializers;
		this.context = context;
		this.ancestors = ancestors;
	}

	public Object getTarget() {
		return null;
	}

	public void start(ObjectTypePair node) {
		if (node == null || node.isSystemOnly()) {
			return;
		}
		if (ancestors.contains(node)) {
			throw new CircularReferenceException(node);
		}
		ancestors.push(node);
	}

	public void end(ObjectTypePair node) {
		if (node != null && !node.isSystemOnly()) {
			ancestors.pop();
		}
	}

	public void startVisitingObject(Object node) {
		assignToRoot(new JsonObject());
	}

	public void visitArray(Object array, Type arrayType) {
		assignToRoot(new JsonArray());
		int length = Array.getLength(array);
		Type componentType = $Gson$Types.getArrayComponentType(arrayType);
		for (int i = 0; i < length; ++i) {
			Object child = Array.get(array, i);
			// we should not get more specific component type yet since it is
			// possible
			// that a custom serializer is registered for the componentType
			addAsArrayElement(new ObjectTypePair(child, componentType, false,
					false));
		}
	}

	public void visitArrayField(FieldAttributes f, Type typeOfF, Object obj) {
		try {
			if (isFieldNull(f, obj)) {
				if (serializeNulls) {
					addChildAsElement(f, JsonNull.INSTANCE);
				}
			} else {
				Object array = getFieldValue(f, obj);
				addAsChildOfObject(f, new ObjectTypePair(array, typeOfF, false,
						false));
			}
		} catch (CircularReferenceException e) {
			throw e.createDetailedException(f);
		}
	}

	public void visitObjectField(FieldAttributes f, Type typeOfF, Object obj) {
		try {
			if (isFieldNull(f, obj)) {
				if (serializeNulls) {
					addChildAsElement(f, JsonNull.INSTANCE);
				}
			} else {
				Object fieldValue = getFieldValue(f, obj);
				// we should not get more specific component type yet since it
				// is
				// possible that a custom
				// serializer is registered for the componentType
				addAsChildOfObject(f, new ObjectTypePair(fieldValue, typeOfF,
						false, false));
			}
		} catch (CircularReferenceException e) {
			throw e.createDetailedException(f);
		}
	}

	public void visitPrimitive(Object obj) {
		JsonElement json = obj == null ? JsonNull.INSTANCE : new JsonPrimitive(
				obj);
		assignToRoot(json);
	}

	private void addAsChildOfObject(FieldAttributes f,
			ObjectTypePair fieldValuePair) {
		JsonElement childElement = getJsonElementForChild(fieldValuePair);
		addChildAsElement(f, childElement);
	}

	private void addChildAsElement(FieldAttributes f, JsonElement childElement) {
		root.getAsJsonObject().add(fieldNamingPolicy.translateName(f),
				childElement);
	}

	private void addAsArrayElement(ObjectTypePair elementTypePair) {
		if (elementTypePair.getObject() == null) {
			root.getAsJsonArray().add(JsonNull.INSTANCE);
		} else {
			JsonElement childElement = getJsonElementForChild(elementTypePair);
			root.getAsJsonArray().add(childElement);
		}
	}

	private JsonElement getJsonElementForChild(ObjectTypePair fieldValueTypePair) {
		JsonSerializationVisitor childVisitor = new JsonSerializationVisitor(
				objectNavigator, fieldNamingPolicy, serializeNulls,
				serializers, context, ancestors);
		objectNavigator.accept(fieldValueTypePair, childVisitor);
		return childVisitor.getJsonElement();
	}

	public boolean visitUsingCustomHandler(ObjectTypePair objTypePair) {
		try {
			Object obj = objTypePair.getObject();
			if (obj == null) {
				if (serializeNulls) {
					assignToRoot(JsonNull.INSTANCE);
				}
				return true;
			}
			JsonElement element = findAndInvokeCustomSerializer(objTypePair);
			if (element != null) {
				assignToRoot(element);
				return true;
			}
			return false;
		} catch (CircularReferenceException e) {
			throw e.createDetailedException(null);
		}
	}

	/**
	 * objTypePair.getObject() must not be null
	 */
	@SuppressWarnings("unchecked")
	private JsonElement findAndInvokeCustomSerializer(ObjectTypePair objTypePair) {
		Pair<JsonSerializer<?>, ObjectTypePair> pair = objTypePair
				.getMatchingHandler(serializers);
		if (pair == null) {
			return null;
		}
		JsonSerializer serializer = pair.first;
		objTypePair = pair.second;
		start(objTypePair);
		try {
			JsonElement element = serializer.serialize(objTypePair.getObject(),
					objTypePair.getType(), context);
			return element == null ? JsonNull.INSTANCE : element;
		} finally {
			end(objTypePair);
		}
	}

	public boolean visitFieldUsingCustomHandler(FieldAttributes f,
			Type declaredTypeOfField, Object parent) {
		try {
			$Gson$Preconditions.checkState(root.isJsonObject());
			Object obj = f.get(parent);
			if (obj == null) {
				if (serializeNulls) {
					addChildAsElement(f, JsonNull.INSTANCE);
				}
				return true;
			}
			ObjectTypePair objTypePair = new ObjectTypePair(obj,
					declaredTypeOfField, false, false);
			JsonElement child = findAndInvokeCustomSerializer(objTypePair);
			if (child != null) {
				addChildAsElement(f, child);
				return true;
			}
			return false;
		} catch (IllegalAccessException e) {
			throw new RuntimeException();
		} catch (CircularReferenceException e) {
			throw e.createDetailedException(f);
		}
	}

	private void assignToRoot(JsonElement newRoot) {
		root = $Gson$Preconditions.checkNotNull(newRoot);
	}

	private boolean isFieldNull(FieldAttributes f, Object obj) {
		return getFieldValue(f, obj) == null;
	}

	private Object getFieldValue(FieldAttributes f, Object obj) {
		try {
			return f.get(obj);
		} catch (IllegalAccessException e) {
			throw new RuntimeException(e);
		}
	}

	public JsonElement getJsonElement() {
		return root;
	}
}