org.cmg.jresp.json.SCELJsonUtil.java Source code

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Here is the source code for org.cmg.jresp.json.SCELJsonUtil.java

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/**
 * Copyright (c) 2012 Concurrency and Mobility Group.
 * Universita' di Firenze
 *   
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *      Michele Loreti
 */
package org.cmg.jresp.json;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;

/**
 * This class provides static methods used to perform recurrent tasks for
 * objects serialization/deserialization.
 * 
 * @author Michele Loreti
 *
 */
public class SCELJsonUtil {

    /**
     * Json tag associated to string referring to {@ling Class} names.
     */
    public static final String TYPE_ID = "type";

    /**
     * Json tag associated to generic objects. The type of the specific object
     * is determined by relying on attribute {@link SCELJsonUtil#TYPE_ID}
     */
    public static final String VALUE_ID = "value";

    /**
     * Serialize an object into a {@link JsonElement}. The object is rendered as
     * a {@link JsonObject} containing two attributes:
     * <ul>
     * <li><code>type</code>, containing a string with the fully qualified name
     * of the serialized object;
     * <li><code>value</code>, containing the {@link JsonElement} associated to
     * the serialized object.
     * </ul>
     * 
     * When the object will be deserialized, the first attribute will be used to
     * identify the object class, while the second one will be used to retrieve
     * object status.
     * 
     * 
     * @param o
     *            object to serialize
     * @param context
     *            Context for serialization
     * @return a json representation of o
     */
    public static JsonElement jsonFromObject(Object o, JsonSerializationContext context) {
        JsonObject json = new JsonObject();
        json.add(SCELJsonUtil.TYPE_ID, new JsonPrimitive(o.getClass().getName()));
        json.add(SCELJsonUtil.VALUE_ID, context.serialize(o));
        return json;
    }

    /**
     * Deserialize an object from a {@link JsonElement}. We assume that the
     * received JsonElement is a {@link JsonObject} providing two attributes:
     * <ul>
     * <li><code>type</code>, containing a string with the fully qualified name
     * of the serialized object;
     * <li><code>value</code>, containing the {@link JsonElement} associated to
     * the serialized object.
     * </ul>
     * 
     * 
     * @param json
     *            element to deserialize
     * @param context
     *            context for serialization
     * @return the object represented by json
     */
    public static Object objectFromJson(JsonElement json, JsonDeserializationContext context) {
        if (!json.isJsonObject()) {
            throw new JsonParseException("Unexpected JsonElement!");
        }
        JsonObject jo = (JsonObject) json;
        if ((!jo.has("type")) || (!jo.has("value"))) {
            throw new JsonParseException("Required attributes are not available!");
        }
        String className = jo.get(TYPE_ID).getAsString();
        try {
            Class<?> c = Class.forName(className);
            return context.deserialize(jo.get(VALUE_ID), c);
        } catch (ClassNotFoundException e) {
            throw new JsonParseException(e);
        }
    }

}