broker-core/src/main/java/org/apache/qpid/server/message/mimecontentconverter/MimeContentConverterRegistry.java

/*
 *
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.qpid.server.message.mimecontentconverter;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableMultimap;
import com.google.common.collect.Multimap;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.qpid.server.plugin.QpidServiceLoader;

public class MimeContentConverterRegistry
{
    private static final Logger LOGGER = LoggerFactory.getLogger(MimeContentConverterRegistry.class);

    private static final Map<String, MimeContentToObjectConverter> _mimeContentToObjectConverters;
    private static final Multimap<Class, ObjectToMimeContentConverter> _classToMimeContentConverters;

    static
    {
        _classToMimeContentConverters = buildClassToMimeConverters();
        _mimeContentToObjectConverters = buildMimeContentToObjectMap();
    }

    private static Multimap<Class, ObjectToMimeContentConverter> buildClassToMimeConverters()
    {
        Multimap<Class, ObjectToMimeContentConverter> classToMineConverters = HashMultimap.create();
        Iterable<ObjectToMimeContentConverter> objectToMimeContentConverters = new QpidServiceLoader().instancesOf(ObjectToMimeContentConverter.class);
        for(ObjectToMimeContentConverter converter : objectToMimeContentConverters)
        {
            Class objectClass = converter.getObjectClass();
            for(ObjectToMimeContentConverter existing : classToMineConverters.get(objectClass))
            {
                if (existing.getRank() == converter.getRank())
                {
                    LOGGER.warn("MIME converter for object class {} has two or more implementations"
                                + " with the same rank {}. It is undefined which one will be used."
                                + " Implementations are: {} {} ",
                                existing.getObjectClass().getName(),
                                existing.getRank(),
                                existing.getClass().getName(),
                                converter.getClass().getName());
                }

            }
            classToMineConverters.put(objectClass, converter);
        }
        classToMineConverters.put(Void.class, new IdentityConverter());
        return ImmutableMultimap.copyOf(classToMineConverters);
    }

    private static Map<String, MimeContentToObjectConverter> buildMimeContentToObjectMap()
    {
        final Map<String, MimeContentToObjectConverter> mimeContentToObjectConverters = new HashMap<>();
        for(MimeContentToObjectConverter converter : (new QpidServiceLoader()).instancesOf(MimeContentToObjectConverter.class))
        {
            final String mimeType = converter.getMimeType();
            final MimeContentToObjectConverter existing = mimeContentToObjectConverters.put(mimeType, converter);
            if (existing != null)
            {
                LOGGER.warn("MIME converter {} for mime type '{}' replaced by {}.",
                            existing.getClass().getName(),
                            existing.getMimeType(),
                            converter.getClass().getName());
            }

        }
        return Collections.unmodifiableMap(mimeContentToObjectConverters);
    }

    public static MimeContentToObjectConverter getMimeContentToObjectConverter(String mimeType)
    {
        return _mimeContentToObjectConverters.get(mimeType);
    }

    public static ObjectToMimeContentConverter getBestFitObjectToMimeContentConverter(Object object)
    {
        ObjectToMimeContentConverter converter = null;
        if (object != null)
        {
            final List<Class<?>> classes = new ArrayList<>(Arrays.asList(object.getClass().getInterfaces()));
            classes.add(object.getClass());
            for (Class<?> i : classes)
            {
                for (ObjectToMimeContentConverter candidate : _classToMimeContentConverters.get(i))
                {
                    if (candidate.isAcceptable(object))
                    {
                        if (converter == null || candidate.getRank() > converter.getRank())
                        {
                            converter = candidate;
                        }
                    }
                }
            }
        }
        return converter;
    }

    public static ObjectToMimeContentConverter getBestFitObjectToMimeContentConverter(Object object, Class<?> typeHint)
    {
        ObjectToMimeContentConverter converter = null;
        for (ObjectToMimeContentConverter candidate : _classToMimeContentConverters.get(typeHint))
        {
            if (candidate.isAcceptable(object))
            {
                if (converter == null || candidate.getRank() > converter.getRank())
                {
                    converter = candidate;
                }
            }
        }

        return converter;
    }
}