FileSystemProviders.java

/*
 * Copyright 2015 Red Hat, Inc. and/or its affiliates.
 *
 * 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 org.uberfire.java.nio.file.api;

import java.net.URI;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.uberfire.java.nio.file.FileSystemNotFoundException;
import org.uberfire.java.nio.file.spi.FileSystemProvider;

import static java.util.Collections.emptyList;
import static java.util.Collections.unmodifiableList;
import static java.util.Collections.unmodifiableMap;
import static org.uberfire.commons.validation.PortablePreconditions.checkNotEmpty;
import static org.uberfire.commons.validation.PortablePreconditions.checkNotNull;

/**
 * Back port of JSR-203 from Java Platform, Standard Edition 7.
 * @see <a href="http://docs.oracle.com/javase/7/docs/api/java/nio/file/spi/FileSystemProvider.html">Original JavaDoc</a>
 */
public final class FileSystemProviders {

    private static final Logger LOGGER = LoggerFactory.getLogger(FileSystemProviders.class);

    private static List<FileSystemProvider> installedProviders = null;
    private static Map<String, FileSystemProvider> mapOfinstalledProviders = null;

    private static void setup() {
        try {
            installedProviders = buildProviders();
            mapOfinstalledProviders = buildProvidersMap();
        } catch (final Throwable ex) {
            LOGGER.error("Can't initialize FileSystemProviders",
                         ex);
        }
        LOGGER.debug("Initialized FileSystemProviders.\n"
                             + "Installed Providers: " + installedProviders + "\n"
                             + "Provider Map: " + mapOfinstalledProviders);
    }

    private static synchronized List<FileSystemProvider> buildProviders() {
        final ServiceLoader<FileSystemProvider> providers = ServiceLoader.load(FileSystemProvider.class);
        if (providers == null) {
            return emptyList();
        }
        final List<FileSystemProvider> result = new ArrayList<FileSystemProvider>();

        for (final FileSystemProvider provider : providers) {
            result.add(provider);
        }
        return unmodifiableList(result);
    }

    private static synchronized Map<String, FileSystemProvider> buildProvidersMap() {
        final Map<String, FileSystemProvider> result = new HashMap<String, FileSystemProvider>(installedProviders.size() + 1);
        for (int i = 0; i < installedProviders.size(); i++) {
            final FileSystemProvider provider = installedProviders.get(i);
            if (i == 0) {
                provider.forceAsDefault();
                result.put("default",
                           provider);
            }
            result.put(provider.getScheme(),
                       provider);
        }
        return unmodifiableMap(result);
    }

    /**
     * Non standard method that provides access to default provider (default:// scheme).
     * @return the default file system provider
     * @throws ServiceConfigurationError
     */
    public static FileSystemProvider getDefaultProvider() throws ServiceConfigurationError {
        if (installedProviders == null) {
            setup();
        }
        return installedProviders.get(0);
    }

    /**
     * Non standard method to resolve a provider based on uri's scheme
     * @param uri the uri
     * @return the file system provider
     */
    public static FileSystemProvider resolveProvider(final URI uri) {
        checkNotNull("uri",
                     uri);
        if (installedProviders == null) {
            setup();
        }

        return getProvider(uri.getScheme());
    }

    private static FileSystemProvider getProvider(final String scheme)
            throws FileSystemNotFoundException, ServiceConfigurationError {
        checkNotEmpty("scheme",
                      scheme);

        final FileSystemProvider fileSystemProvider = mapOfinstalledProviders.get(scheme);

        if (fileSystemProvider == null) {
            throw new FileSystemNotFoundException("Provider '" + scheme + "' not found");
        }

        return fileSystemProvider;
    }

    /**
     * @throws ServiceConfigurationError
     * @see <a href="http://docs.oracle.com/javase/7/docs/api/java/nio/file/spi/FileSystemProvider.html#installedProviders()">Original JavaDoc</a>
     */
    public static List<FileSystemProvider> installedProviders() throws ServiceConfigurationError {
        if (installedProviders == null) {
            setup();
        }
        return installedProviders;
    }
}