code/spi-support/src/main/java/org/apache/tamaya/spisupport/DefaultServiceContext.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.tamaya.spisupport;

import org.apache.tamaya.ConfigException;
import org.apache.tamaya.spi.ClassloaderAware;
import org.apache.tamaya.spi.ServiceContext;

import java.text.MessageFormat;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Supplier;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * This class implements the (default) {@link ServiceContext} interface and hereby uses the JDK
 * {@link ServiceLoader} to load the services required.
 */
public final class DefaultServiceContext implements ServiceContext {
    private static final Logger LOG = Logger.getLogger(DefaultServiceContext.class.getName());

    private ClassLoader classLoader;
    /**
     * List current services loaded, per class.
     */
    private final ConcurrentHashMap<Class<?>, List<Object>> servicesLoaded = new ConcurrentHashMap<>();
    /**
     * Singletons.
     */
    private final Map<Class<?>, Object> singletons = new ConcurrentHashMap<>();
    @SuppressWarnings("rawtypes")
    private Map<Class, Class> factoryTypes = new ConcurrentHashMap<>();

    @Override
    public <T> T getService(Class<T> serviceType, Supplier<T> supplier) {
        T service = (T)singletons.get(serviceType);
        if(service!=null){
            return service;
        }
        Collection<T> services = loadServices(serviceType, null);
        if (services.isEmpty() && supplier!=null){
            T instance = supplier.get();
            if(instance instanceof ClassloaderAware){
                ((ClassloaderAware)instance).init(this.classLoader);
            }
            register(serviceType, instance, true);
            return instance;
        }
        T t = getServiceWithHighestPriority(services, serviceType);
        if(t!=null) {
            this.singletons.put(serviceType, t);
        }
        return t;
    }

    @Override
    public <T> T create(Class<T> serviceType, Supplier<T> supplier) {
        Class<? extends T> implType = factoryTypes.get(serviceType);
        if(implType==null) {
            Collection<T> services = loadServices(serviceType, null);
            if (services.isEmpty()) {
                if(supplier!=null){
                    return supplier.get();
                }
                return null;
            } else {
                return getServiceWithHighestPriority(services, serviceType);
            }
        }
        try {
            return implType.newInstance();
        } catch (Exception e) {
            LOG.log(Level.SEVERE, "Failed to createObject instance of " + implType.getName(), e);
            return  null;
        }
    }

    /**
     * @param services to scan
     * @param <T>      type of the service
     *
     * @return the service with the highest {@link Priority#value()}
     *
     * @throws ConfigException if there are multiple service implementations with the maximum priority
     */
    private <T> T getServiceWithHighestPriority(Collection<T> services, Class<T> serviceType) {
        T highestService = null;
        // we do not need the priority stuff if the createList contains only one element
        if (services.size() == 1) {
            highestService = services.iterator().next();
            this.factoryTypes.put(serviceType, highestService.getClass());
            return highestService;
        }

        Integer highestPriority = null;
        int highestPriorityServiceCount = 0;

        for (T service : services) {
            int prio = ServiceContext.getPriority(service);
            if (highestPriority == null || highestPriority < prio) {
                highestService = service;
                highestPriorityServiceCount = 1;
                highestPriority = prio;
            } else if (highestPriority == prio) {
                highestPriorityServiceCount++;
            }
        }

        if (highestPriorityServiceCount > 1) {
            throw new ConfigException(MessageFormat.format("Found {0} implementations for Service {1} with Priority {2}: {3}",
                    highestPriorityServiceCount,
                    serviceType.getName(),
                    highestPriority,
                    services));
        }
        if(highestService!=null) {
            this.factoryTypes.put(serviceType, highestService.getClass());
        }
        return highestService;
    }

    /**
     * Loads and registers services.
     *
     * @param <T>         the concrete type.
     * @param serviceType The service type.
     * @return the items found, never {@code null}.
     */
    @Override
    public <T> List<T> getServices(final Class<T> serviceType, Supplier<List<T>> supplier) {
        @SuppressWarnings("unchecked")
        List<T> found = (List<T>) servicesLoaded.get(serviceType);
        if (found != null) {
            return found;
        }
        List<T> services = loadServices(serviceType, supplier);
        @SuppressWarnings("unchecked")
        final List<T> previousServices = List.class.cast(servicesLoaded.putIfAbsent(serviceType, (List<Object>) services));
        return previousServices != null ? previousServices : services;
    }

    /**
     * Loads services.
     *
     * @param <T>         the concrete type.
     * @param serviceType The service type.
     * @return the items found, never {@code null}.
     */
    private <T> List<T> loadServices(final Class<T> serviceType, Supplier<List<T>> supplier) {
        List<T> services = new ArrayList<>();
        try {
            for (T t : ServiceLoader.load(serviceType, classLoader)) {
                if(t instanceof ClassloaderAware){
                    ((ClassloaderAware)t).init(classLoader);
                }
                services.add(t);
            }
            Collections.sort(services, PriorityServiceComparator.getInstance());
            services = Collections.unmodifiableList(services);
        } catch (ServiceConfigurationError e) {
            if(supplier!=null){
                services = supplier.get();
            }else {
                LOG.log(Level.WARNING,
                        "Error loading services current type " + serviceType, e);
            }
            if(services==null){
                services = Collections.emptyList();
            }
        }
        return services;
    }

    @Override
    public <T> T register(Class<T> serviceType, T instance, boolean force) {
        if(force){
            singletons.put(serviceType, instance);
        }else {
            singletons.putIfAbsent(serviceType, instance);
        }
        return (T)singletons.get(serviceType);
    }

    @Override
    public <T> List<T> register(Class<T> type, List<T> instances, boolean force) {
        if(force){
            servicesLoaded.put(type, (List)instances);
        }else {
            servicesLoaded.putIfAbsent(type, (List)instances);
        }
        return (List<T>)servicesLoaded.get(type);
    }

    @Override
    public void reset() {
        servicesLoaded.clear();
        singletons.clear();
        factoryTypes.clear();
    }


    @Override
    public ClassLoader getClassLoader() {
        return classLoader;
    }

    @Override
    public void init(ClassLoader classLoader) {
        if(this.classLoader==null){
            this.classLoader = Objects.requireNonNull(classLoader);
        }else{
            throw new IllegalStateException("Classloader already setCurrent on this context.");
        }
    }

}