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

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

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// ***************************************************************************
// *  Copyright 2012 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.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.TreeSet;

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

/**
 * Translator that converts a json array into a list.
 * @author jmolnar
 *
 */
public class JsonArrayToCollectionTranslator implements Translator {
    private final Translator elementTranslator;
    private final Class<?> collectionType;
    private final Constructor<?> constructor;

    /**
     * Empty default constructor.
     */
    public JsonArrayToCollectionTranslator(Translator theElementTranslator, Class<?> theCollectionType) {
        Preconditions.checkNotNull(theElementTranslator);
        Preconditions.checkNotNull(theCollectionType, "need a collection type");
        Preconditions.checkArgument(Collection.class.isAssignableFrom(theCollectionType),
                "needs to implement collection");

        elementTranslator = theElementTranslator;
        if (Modifier.isAbstract(theCollectionType.getModifiers()) || theCollectionType.isInterface()) {
            if (theCollectionType.isAssignableFrom(ArrayList.class)) {
                collectionType = ArrayList.class; // a list
            } else if (theCollectionType.isAssignableFrom(HashSet.class)) {
                collectionType = HashSet.class; // a set 
            } else if (theCollectionType.isAssignableFrom(TreeSet.class)) {
                collectionType = TreeSet.class; // a sorted set
            } else {
                throw new IllegalArgumentException(String.format("unclear how to use the collection of type '%s'",
                        theCollectionType.getName()));
            }
        } else {
            collectionType = theCollectionType;
        }
        try {
            constructor = collectionType.getDeclaredConstructor();
        } catch (SecurityException e) {
            throw new IllegalArgumentException(String.format(
                    "unable to get constructor for collection of type '%s'", theCollectionType.getName()), e);
        } catch (NoSuchMethodException e) {
            throw new IllegalArgumentException(String.format(
                    "unable to get constructor for collection of type '%s'", theCollectionType.getName()), e);
        }
    }

    /**
     * Translates the received object into a list.
     * If the object is of the wrong type, a TranslationException will occur.
     */
    @Override
    public Object translate(Object anObject) {
        Object returnValue;

        if (anObject == null || anObject.equals(JsonNull.INSTANCE)) {
            returnValue = null;
        } else {
            try {
                JsonArray jsonArray = (JsonArray) anObject;
                @SuppressWarnings("unchecked")
                Collection<Object> collection = (Collection<Object>) constructor.newInstance();

                for (JsonElement element : jsonArray) {
                    collection.add(elementTranslator.translate(element));
                }

                returnValue = collection;

            } catch (ClassCastException e) {
                throw new TranslationException(e);
            } catch (NullPointerException e) {
                throw new TranslationException(String.format("Unable to use null in the collection of type '%s'",
                        collectionType.getName()), e);
            } catch (InstantiationException e) {
                throw new TranslationException(
                        String.format("Unable to create a collection of type '%s'", collectionType.getName()), e);
            } catch (IllegalArgumentException e) {
                throw new TranslationException(
                        String.format("Unable to create a collection of type '%s'", collectionType.getName()), e);
            } catch (InvocationTargetException e) {
                throw new TranslationException(
                        String.format("Unable to create a collection of type '%s'", collectionType.getName()), e);
            } catch (IllegalAccessException e) {
                throw new TranslationException(
                        String.format("Unable to create a collection of type '%s'", collectionType.getName()), e);
            }
        }
        return returnValue;
    }
}