ReflectiveTypeAdapter.java

/*
 * 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.smartandroid.sa.json.internal.bind;

import java.io.IOException;
import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.LinkedHashMap;
import java.util.Map;

import com.smartandroid.sa.json.internal.$Gson$Types;
import com.smartandroid.sa.json.internal.UnsafeAllocator;
import com.smartandroid.sa.json.reflect.TypeToken;
import com.smartandroid.sa.json.stream.JsonReader;
import com.smartandroid.sa.json.stream.JsonToken;
import com.smartandroid.sa.json.stream.JsonWriter;

/**
 * Adapts the fields of an object to the properties of a JSON object.
 */
public final class ReflectiveTypeAdapter<T> extends TypeAdapter<T> {
	public static final Factory FACTORY = new FactoryImpl();

	private static final UnsafeAllocator unsafeAllocator = UnsafeAllocator
			.create();
	private final Class<? super T> rawType;
	private final Constructor<? super T> constructor;
	private final Map<String, BoundField> map;
	private final BoundField[] boundFields;

	ReflectiveTypeAdapter(Class<? super T> rawType,
			Constructor<? super T> constructor, Map<String, BoundField> map) {
		this.rawType = rawType;
		this.constructor = constructor;
		this.map = map;
		this.boundFields = map.values().toArray(new BoundField[map.size()]);
	}

	@SuppressWarnings("unchecked")
	// the '? super T' is a raw T (the only kind we can construct)
	public T read(JsonReader reader) throws IOException {
		if (reader.peek() == JsonToken.NULL) {
			reader.nextNull(); // TODO: does this belong here?
			return null;
		}

		T instance;
		if (constructor != null) {
			instance = (T) Reflection.newInstance(constructor);
		} else {
			try {
				instance = (T) unsafeAllocator.newInstance(rawType);
			} catch (Exception e) {
				throw new RuntimeException(
						("Unable to invoke no-args constructor for "
								+ rawType.getName() + ". Register an InstanceCreator with Gson for this type may fix this problem."),
						e);
			}
		}

		// TODO: null out the other fields?

		reader.beginObject();
		try {
			while (reader.hasNext()) {
				String name = reader.nextName();
				BoundField field = map.get(name);
				if (field == null || !field.deserialized) {
					// TODO: define a better policy
					reader.skipValue();
				} else {
					field.read(reader, instance);
				}
			}
		} catch (IllegalAccessException e) {
			throw new AssertionError();
		}
		reader.endObject();
		return instance;
	}

	public void write(JsonWriter writer, T value) throws IOException {
		if (value == null) {
			writer.nullValue(); // TODO: better policy here?
			return;
		}

		writer.beginObject();
		try {
			for (BoundField boundField : boundFields) {
				if (boundField.serialized) {
					writer.name(boundField.name);
					boundField.write(writer, value);
				}
			}
		} catch (IllegalAccessException e) {
			throw new AssertionError();
		}
		writer.endObject();
	}

	static BoundField createBoundField(final MiniGson context,
			final Field field, final String name, final TypeToken<?> fieldType,
			boolean serialize, boolean deserialize) {
		// special casing primitives here saves ~5% on Android...
		return new BoundField(name, serialize, deserialize) {
			final TypeAdapter<?> typeAdapter = context.getAdapter(fieldType);

			@SuppressWarnings("unchecked")
			// the type adapter and field type always agree
			@Override
			void write(JsonWriter writer, Object value) throws IOException,
					IllegalAccessException {
				Object fieldValue = field.get(value);
				TypeAdapter t = new TypeAdapterRuntimeTypeWrapper(context,
						this.typeAdapter, fieldType.getType());
				t.write(writer, fieldValue);
			}

			@Override
			void read(JsonReader reader, Object value) throws IOException,
					IllegalAccessException {
				Object fieldValue = typeAdapter.read(reader);
				field.set(value, fieldValue);
			}
		};
	}

	public static class FactoryImpl implements Factory {
		public boolean serializeField(Class<?> declaringClazz, Field f,
				Type declaredType) {
			return true;
		}

		public boolean deserializeField(Class<?> declaringClazz, Field f,
				Type declaredType) {
			return true;
		}

		public String getFieldName(Class<?> declaringClazz, Field f,
				Type declaredType) {
			return f.getName();
		}

		public <T> TypeAdapter<T> create(MiniGson context, TypeToken<T> type) {
			Class<? super T> raw = type.getRawType();

			if (!Object.class.isAssignableFrom(raw)) {
				return null; // it's a primitive!
			}

			Constructor<? super T> constructor = null;
			try {
				constructor = raw.getDeclaredConstructor();
			} catch (NoSuchMethodException ignored) {
			}

			return new ReflectiveTypeAdapter<T>(raw, constructor,
					getBoundFields(context, type, raw));
		}

		private Map<String, BoundField> getBoundFields(MiniGson context,
				TypeToken<?> type, Class<?> raw) {
			Map<String, BoundField> result = new LinkedHashMap<String, BoundField>();
			if (raw.isInterface()) {
				return result;
			}

			Type declaredType = type.getType();
			while (raw != Object.class) {
				Field[] fields = raw.getDeclaredFields();
				AccessibleObject.setAccessible(fields, true);
				for (Field field : fields) {
					boolean serialize = serializeField(raw, field, declaredType);
					boolean deserialize = deserializeField(raw, field,
							declaredType);
					if (serialize || deserialize) {
						Type fieldType = $Gson$Types.resolve(type.getType(),
								raw, field.getGenericType());
						BoundField boundField = createBoundField(context,
								field, getFieldName(raw, field, declaredType),
								TypeToken.get(fieldType), serialize,
								deserialize);
						BoundField previous = result.put(boundField.name,
								boundField);
						if (previous != null) {
							throw new IllegalArgumentException(declaredType
									+ " declares multiple JSON fields named "
									+ previous.name);
						}
					}
				}
				type = TypeToken.get($Gson$Types.resolve(type.getType(), raw,
						raw.getGenericSuperclass()));
				raw = type.getRawType();
			}
			return result;
		}
	}

	static abstract class BoundField {
		final String name;
		final boolean serialized;
		final boolean deserialized;

		protected BoundField(String name, boolean serialized,
				boolean deserialized) {
			this.name = name;
			this.serialized = serialized;
			this.deserialized = deserialized;
		}

		abstract void write(JsonWriter writer, Object value)
				throws IOException, IllegalAccessException;

		abstract void read(JsonReader reader, Object value) throws IOException,
				IllegalAccessException;
	}
}