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

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Here is the source code for com.talvish.tales.serialization.json.translators.JsonObjectToPolymorphicObjectTranslator.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.google.gson.JsonPrimitive;
import com.talvish.tales.parts.translators.TranslationException;
import com.talvish.tales.parts.translators.Translator;
import com.talvish.tales.serialization.TypeFormatAdapter;

public class JsonObjectToPolymorphicObjectTranslator implements Translator {
    private final Map<String, TypeFormatAdapter> typeAdapters = new HashMap<>(2);

    /**
     * Constructor taking the needed adapters.
     */
    public JsonObjectToPolymorphicObjectTranslator(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.getName()), String.format(
                    "Attempting to add type adapter '%s' more than once.", typeAdapter.getType().getName()));
            typeAdapters.put(typeAdapter.getName(), 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 || anObject.equals(JsonNull.INSTANCE)) {
            returnValue = null;
        } else {
            try {
                // need to extract two things, the "value" and the "value_type"
                // and if they don't exist then we have a problem
                JsonObject jsonObject = (JsonObject) anObject;
                JsonPrimitive valueTypeJson = jsonObject.getAsJsonPrimitive("value_type");
                JsonElement valueJson = jsonObject.get("value");

                if (valueTypeJson == null || !valueTypeJson.isString()) {
                    throw new TranslationException(String.format("The associate value type is missing."));
                } else if (valueJson == null) {
                    throw new TranslationException(String.format("The associate value for type '%s' is missing.",
                            valueTypeJson.getAsString()));
                } else {
                    String valueTypeString = valueTypeJson.getAsString();
                    TypeFormatAdapter typeAdapter = typeAdapters.get(valueTypeString);

                    if (typeAdapter == null) {
                        throw new TranslationException(String
                                .format("Json is referring to a type '%s' that isn't supported.", valueTypeString));
                    } else {
                        returnValue = typeAdapter.getFromFormatTranslator().translate(valueJson);
                    }
                }

                // TODO: catch the various gson json exceptions
            } catch (ClassCastException e) {
                throw new TranslationException(e);
            }
        }
        return returnValue;
    }
}