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/*
 * Copyright 2015 The gRPC Authors
 *
 * 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.ServiceProviders.PriorityAccessor;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * Provider of managed channels for transport agnostic consumption.
 *
 * 

Implementations should not 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 { @VisibleForTesting static final Iterable> HARDCODED_CLASSES = new HardcodedClasses(); private static final ManagedChannelProvider provider = ServiceProviders.load( ManagedChannelProvider.class, HARDCODED_CLASSES, ManagedChannelProvider.class.getClassLoader(), new PriorityAccessor() { @Override public boolean isAvailable(ManagedChannelProvider provider) { return provider.isAvailable(); } @Override public int getPriority(ManagedChannelProvider provider) { return provider.priority(); } }); /** * 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, grpc-netty, or grpc-netty-shaded " + "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 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); } } private static final class HardcodedClasses implements Iterable> { @Override public Iterator> iterator() { List> list = new ArrayList<>(); try { list.add(Class.forName("io.grpc.okhttp.OkHttpChannelProvider")); } catch (ClassNotFoundException ex) { // ignore } try { list.add(Class.forName("io.grpc.netty.NettyChannelProvider")); } catch (ClassNotFoundException ex) { // ignore } return list.iterator(); } } }





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