funf.config.SingletonTypeAdapterFactory.java Source code

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Here is the source code for funf.config.SingletonTypeAdapterFactory.java

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/**
 * 
 * Funf: Open Sensing Framework
 * Copyright (C) 2010-2011 Nadav Aharony, Wei Pan, Alex Pentland.
 * Acknowledgments: Alan Gardner
 * Contact: nadav@media.mit.edu
 * 
 * This file is part of Funf.
 * 
 * Funf is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 * 
 * Funf is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with Funf. If not, see <http://www.gnu.org/licenses/>.
 * 
 */
package funf.config;

import static funf.json.JsonUtils.immutable;

import java.io.IOException;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.internal.Streams;
import bind.JsonTreeReader;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

/**
 * Same configuration should return the same object.  
 * A cache of each object created is kept to ensure this.
 * 
 * TODO: should probably have weak refs, so that we can garbage collect unused items.
 * 
 * @author alangardner
 *
 */
public class SingletonTypeAdapterFactory implements TypeAdapterFactory {

    private RuntimeTypeAdapterFactory delegate;
    private Map<String, Object> cache;

    public SingletonTypeAdapterFactory(RuntimeTypeAdapterFactory delegate) {
        this.delegate = delegate;
        this.cache = new HashMap<String, Object>();
    }

    @Override
    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        TypeAdapter<T> adapter = delegate.create(gson, type);
        return adapter == null ? null : new SingletonTypeAdapter<T>(adapter, type);
    }

    public Collection<Object> getCached() {
        return this.cache.values();
    }

    public void clearCache(Object o) {
        synchronized (cache) {
            Set<String> toRemove = new HashSet<String>();
            for (Map.Entry<String, Object> entry : cache.entrySet()) {
                if (o == entry.getValue()) {
                    toRemove.add(entry.getKey());
                }
            }
            for (String key : toRemove) {
                cache.remove(key);
            }
        }
    }

    public void clearCache() {
        synchronized (cache) {
            cache.clear();
        }
    }

    public class SingletonTypeAdapter<E> extends TypeAdapter<E> {

        private TypeAdapter<E> typeAdapter;
        private TypeToken<E> type;

        public SingletonTypeAdapter(TypeAdapter<E> typeAdapter, TypeToken<E> type) {
            this.typeAdapter = typeAdapter;
            this.type = type;
        }

        @Override
        public void write(JsonWriter out, E value) throws IOException {
            typeAdapter.write(out, value);
        }

        @Override
        public E read(JsonReader in) throws IOException {
            JsonElement el = Streams.parse(in);
            Class<? extends E> runtimeType = delegate.getRuntimeType(el, type);
            String configString = runtimeType.toString() + immutable(el).toString();
            // TODO: surround this in a try catch class cast exception
            @SuppressWarnings("unchecked")
            E object = (E) cache.get(configString);
            if (object == null) {
                object = typeAdapter.read(new JsonTreeReader(el));
                cache.put(configString, object);
            }
            return object;
        }

        public void clearCache() {
            cache.clear();
        }
    }
}