com.talvish.tales.serialization.json.translators.PolymorphicObjectToJsonObjectTranslator.java Source code

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Here is the source code for com.talvish.tales.serialization.json.translators.PolymorphicObjectToJsonObjectTranslator.java

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// ***************************************************************************
// *  Copyright 2014 Joseph Molnar
// *
// *  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.talvish.tales.serialization.json.translators;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.common.base.Preconditions;
import com.google.gson.JsonElement;
import com.google.gson.JsonNull;
import com.google.gson.JsonObject;
import com.talvish.tales.parts.translators.TranslationException;
import com.talvish.tales.parts.translators.Translator;
import com.talvish.tales.serialization.TypeFormatAdapter;

/**
 * A translator that looks at the type to be translated and picks an appropriate translator.
 * The translator doesn't support more than one class where the only difference is generic
 * type parameters since the information is not available during the serialization process.
 * Fixing this may be impossible or at least very difficult to do in Java.
 * @author jmolnar
 *
 */
public class PolymorphicObjectToJsonObjectTranslator implements Translator {
    private final Map<Class<?>, TypeFormatAdapter> typeAdapters = new HashMap<>(2);

    /**
     * Constructor taking the needed adapters.
     */
    public PolymorphicObjectToJsonObjectTranslator(List<TypeFormatAdapter> theTypeAdapters) {
        Preconditions.checkNotNull(theTypeAdapters);
        Preconditions.checkArgument(theTypeAdapters.size() > 0, "Need at least one value type adapter.");

        for (TypeFormatAdapter typeAdapter : theTypeAdapters) {
            Preconditions.checkArgument(!typeAdapters.containsKey(typeAdapter.getType().getUnderlyingClass()),
                    String.format(
                            "Attempting to add type adapter '%s' more than once (differences in generic type parameters are not sufficient).",
                            typeAdapter.getType().getUnderlyingClass().getName()));
            typeAdapters.put(typeAdapter.getType().getUnderlyingClass(), typeAdapter);
        }
    }

    /**
     * Translates the received object into the appropriate json representation.
     * If the object is of the wrong type or the translator used doesn't produce
     * JsonElements's then a TranslationException will occur.
     */
    @Override
    public Object translate(Object anObject) {
        Object returnValue;

        if (anObject == null) {
            returnValue = JsonNull.INSTANCE;
        } else {
            TypeFormatAdapter typeAdapter = typeAdapters.get(anObject.getClass());
            if (typeAdapter == null) {
                throw new TranslationException(String.format(
                        "An object of type '%s' was attempting to be converted to a json object, but this object isn't supported",
                        anObject.getClass().getName()));
            } else {
                try {
                    JsonObject jsonEntry = new JsonObject();

                    jsonEntry.addProperty("value_type", typeAdapter.getName());
                    jsonEntry.add("value", (JsonElement) typeAdapter.getToFormatTranslator().translate(anObject));

                    returnValue = jsonEntry;

                } catch (ClassCastException e) {
                    throw new TranslationException(e);
                }
            }
        }
        return returnValue;
    }
}