cern.c2mon.shared.util.json.GsonFactory.java Source code

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Here is the source code for cern.c2mon.shared.util.json.GsonFactory.java

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/******************************************************************************
 * Copyright (C) 2010-2016 CERN. All rights not expressly granted are reserved.
 * 
 * This file is part of the CERN Control and Monitoring Platform 'C2MON'.
 * C2MON 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.
 * 
 * C2MON 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 C2MON. If not, see <http://www.gnu.org/licenses/>.
 *****************************************************************************/
package cern.c2mon.shared.util.json;

import java.lang.reflect.Type;
import java.sql.Timestamp;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;

/**
 * Factory class for creating a customized GSON builder that is used for
 * serializing/deserializing C2MON client messages. 
 *
 * @author Matthias Braeger
 */
public abstract class GsonFactory {

    /**
     * Hidden default constructor
     */
    private GsonFactory() {
        // Do nothing
    }

    /**
     * Creates a Gson Builder that converts by default a time stamp to a long
     * value. Furthermore, in case of an <code>Object</code> field it does not
     * try to deserialize the object but stores instead the Json String to that
     * field. The deserialization has then to be handled in an extra step once the
     * final Object class information is available. 
     * @return The Gson Builder to serialize/deserialize Json messages
     */
    public static GsonBuilder createGsonBuilder() {
        GsonBuilder gsonBuilder = new GsonBuilder().registerTypeAdapter(Timestamp.class, new TimestampSerializer())
                .registerTypeAdapter(Timestamp.class, new TimestampDeserializer())
                .registerTypeAdapter(Object.class, new TagValueDeserializer());

        return gsonBuilder;
    }

    /**
     * Creates a Gson instance that converts by default a time stamp to a long
     * value. Furthermore, in case of an <code>Object</code> field it does not
     * try to deserialize the object but stores instead the Json String to that
     * field. The deserialization has then to be handled in an extra step once the
     * final Object class information is available.
     * @return An instance of Gson configured with the options currently set in this builder
     * @see #createGsonBuilder()
     */
    public static final Gson createGson() {
        return createGsonBuilder().create();
    }

    /**
     * This private class is used by Gson to serialize correctly the Timestamp objects
     *
     * @author Matthias Braeger
     */
    private static final class TimestampSerializer implements JsonSerializer<Timestamp> {
        @Override
        public JsonElement serialize(final Timestamp src, final Type typeOfSrc,
                final JsonSerializationContext context) {
            return new JsonPrimitive(src.getTime());
        }
    }

    /**
     * This private class is used by Gson to deserialize correctly the Timestamp objects
     *
     * @author Matthias Braeger
     */
    private static final class TimestampDeserializer implements JsonDeserializer<Timestamp> {
        @Override
        public Timestamp deserialize(final JsonElement json, final Type typeOfT,
                final JsonDeserializationContext context) throws JsonParseException {
            return new Timestamp(json.getAsJsonPrimitive().getAsLong());
        }
    }

    /**
     * This private class assures that the <code>tagValue</code> Json represenetation
     * is not deserialized by Json. This is not possible at this stage since the Object
     * type information gets lost while serializing. But we stored it in the
     * <code>valueClassName</code> variable and deserialize then later in the 
     * <code>getValue()</code> method.
     *
     * @author Matthias Braeger
     * @see TransferTagValueImpl#getValue()
     */
    private static final class TagValueDeserializer implements JsonDeserializer<String> {
        @Override
        public String deserialize(final JsonElement json, final Type typeOfT,
                final JsonDeserializationContext context) throws JsonParseException {
            return json.toString().trim();
        }
    }
}