| /* |
| * Copyright 2015, gRPC Authors All rights reserved. |
| * |
| * 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 io.grpc; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| import java.util.ArrayList; |
| import java.util.Collections; |
| import java.util.Comparator; |
| import java.util.List; |
| import java.util.ServiceConfigurationError; |
| import java.util.ServiceLoader; |
| |
| /** |
| * Provider of managed channels for transport agnostic consumption. |
| * |
| * <p>Implementations <em>should not</em> throw. If they do, it may interrupt class loading. If |
| * exceptions may reasonably occur for implementation-specific reasons, implementations should |
| * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. |
| */ |
| @Internal |
| public abstract class ManagedChannelProvider { |
| private static final ManagedChannelProvider provider |
| = load(ManagedChannelProvider.class.getClassLoader()); |
| |
| @VisibleForTesting |
| static ManagedChannelProvider load(ClassLoader classLoader) { |
| Iterable<ManagedChannelProvider> candidates; |
| if (isAndroid()) { |
| candidates = getCandidatesViaHardCoded(classLoader); |
| } else { |
| candidates = getCandidatesViaServiceLoader(classLoader); |
| } |
| List<ManagedChannelProvider> list = new ArrayList<ManagedChannelProvider>(); |
| for (ManagedChannelProvider current : candidates) { |
| if (!current.isAvailable()) { |
| continue; |
| } |
| list.add(current); |
| } |
| if (list.isEmpty()) { |
| return null; |
| } else { |
| return Collections.max(list, new Comparator<ManagedChannelProvider>() { |
| @Override |
| public int compare(ManagedChannelProvider f1, ManagedChannelProvider f2) { |
| return f1.priority() - f2.priority(); |
| } |
| }); |
| } |
| } |
| |
| /** |
| * Loads service providers for the {@link ManagedChannelProvider} service using |
| * {@link ServiceLoader}. |
| */ |
| @VisibleForTesting |
| public static Iterable<ManagedChannelProvider> getCandidatesViaServiceLoader( |
| ClassLoader classLoader) { |
| return ServiceLoader.load(ManagedChannelProvider.class, classLoader); |
| } |
| |
| /** |
| * Load providers from a hard-coded list. This avoids using getResource(), which has performance |
| * problems on Android (see https://github.com/grpc/grpc-java/issues/2037). Any provider that may |
| * be used on Android is free to be added here. |
| */ |
| @VisibleForTesting |
| public static Iterable<ManagedChannelProvider> getCandidatesViaHardCoded( |
| ClassLoader classLoader) { |
| List<ManagedChannelProvider> list = new ArrayList<ManagedChannelProvider>(); |
| try { |
| list.add(create(Class.forName("io.grpc.okhttp.OkHttpChannelProvider", true, classLoader))); |
| } catch (ClassNotFoundException ex) { |
| // ignore |
| } |
| try { |
| list.add(create(Class.forName("io.grpc.netty.NettyChannelProvider", true, classLoader))); |
| } catch (ClassNotFoundException ex) { |
| // ignore |
| } |
| return list; |
| } |
| |
| @VisibleForTesting |
| static ManagedChannelProvider create(Class<?> rawClass) { |
| try { |
| return rawClass.asSubclass(ManagedChannelProvider.class).getConstructor().newInstance(); |
| } catch (Throwable t) { |
| throw new ServiceConfigurationError( |
| "Provider " + rawClass.getName() + " could not be instantiated: " + t, t); |
| } |
| } |
| |
| /** |
| * Returns the ClassLoader-wide default channel. |
| * |
| * @throws ProviderNotFoundException if no provider is available |
| */ |
| public static ManagedChannelProvider provider() { |
| if (provider == null) { |
| throw new ProviderNotFoundException("No functional channel service provider found. " |
| + "Try adding a dependency on the grpc-okhttp or grpc-netty artifact"); |
| } |
| return provider; |
| } |
| |
| /** |
| * Returns whether current platform is Android. |
| */ |
| protected static boolean isAndroid() { |
| try { |
| Class.forName("android.app.Application", /*initialize=*/ false, null); |
| return true; |
| } catch (Exception e) { |
| // If Application isn't loaded, it might as well not be Android. |
| return false; |
| } |
| } |
| |
| /** |
| * Whether this provider is available for use, taking the current environment into consideration. |
| * If {@code false}, no other methods are safe to be called. |
| */ |
| protected abstract boolean isAvailable(); |
| |
| /** |
| * A priority, from 0 to 10 that this provider should be used, taking the current environment into |
| * consideration. 5 should be considered the default, and then tweaked based on environment |
| * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should |
| * be last in line. |
| */ |
| protected abstract int priority(); |
| |
| /** |
| * Creates a new builder with the given host and port. |
| */ |
| protected abstract ManagedChannelBuilder<?> builderForAddress(String name, int port); |
| |
| /** |
| * Creates a new builder with the given target URI. |
| */ |
| protected abstract ManagedChannelBuilder<?> builderForTarget(String target); |
| |
| /** |
| * Thrown when no suitable {@link ManagedChannelProvider} objects can be found. |
| */ |
| public static final class ProviderNotFoundException extends RuntimeException { |
| private static final long serialVersionUID = 1; |
| |
| public ProviderNotFoundException(String msg) { |
| super(msg); |
| } |
| } |
| } |