| /* |
| * 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 io.grpc.ManagedChannelProvider.ProviderNotFoundException; |
| import java.util.ServiceLoader; |
| |
| /** |
| * Provider of servers 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 ServerProvider { |
| private static final ServerProvider provider = |
| load(ServerProvider.class.getClassLoader()); |
| |
| @VisibleForTesting |
| static final ServerProvider load(ClassLoader cl) { |
| ServiceLoader<ServerProvider> providers = ServiceLoader.load(ServerProvider.class, cl); |
| ServerProvider best = null; |
| |
| for (ServerProvider current : providers) { |
| if (!current.isAvailable()) { |
| continue; |
| } else if (best == null) { |
| best = current; |
| } else if (current.priority() > best.priority()) { |
| best = current; |
| } |
| } |
| return best; |
| } |
| |
| /** |
| * Returns the ClassLoader-wide default server. |
| * |
| * @throws ProviderNotFoundException if no provider is available |
| */ |
| public static ServerProvider provider() { |
| if (provider == null) { |
| throw new ProviderNotFoundException("No functional server found. " |
| + "Try adding a dependency on the grpc-netty artifact"); |
| } |
| return provider; |
| } |
| |
| /** |
| * 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 port. |
| */ |
| protected abstract ServerBuilder<?> builderForPort(int port); |
| } |
| |