1 /* 2 * Copyright 2016 The gRPC Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package io.grpc; 18 19 import io.grpc.NameResolver.Factory; 20 import java.net.InetSocketAddress; 21 import java.net.SocketAddress; 22 import java.util.Collection; 23 import java.util.Collections; 24 25 /** 26 * Provider of name resolvers for name agnostic consumption. 27 * 28 * <p>Implementations can be automatically discovered by gRPC via Java's SPI mechanism. For 29 * automatic discovery, the implementation must have a zero-argument constructor and include 30 * a resource named {@code META-INF/services/io.grpc.NameResolverProvider} in their JAR. The 31 * file's contents should be the implementation's class name. Implementations that need arguments in 32 * their constructor can be manually registered by {@link NameResolverRegistry#register}. 33 * 34 * <p>Implementations <em>should not</em> throw. If they do, it may interrupt class loading. If 35 * exceptions may reasonably occur for implementation-specific reasons, implementations should 36 * generally handle the exception gracefully and return {@code false} from {@link #isAvailable()}. 37 */ 38 @ExperimentalApi("https://github.com/grpc/grpc-java/issues/4159") 39 public abstract class NameResolverProvider extends NameResolver.Factory { 40 /** 41 * Whether this provider is available for use, taking the current environment into consideration. 42 * If {@code false}, no other methods are safe to be called. 43 * 44 * @since 1.0.0 45 */ isAvailable()46 protected abstract boolean isAvailable(); 47 48 /** 49 * A priority, from 0 to 10 that this provider should be used, taking the current environment into 50 * consideration. 5 should be considered the default, and then tweaked based on environment 51 * detection. A priority of 0 does not imply that the provider wouldn't work; just that it should 52 * be last in line. 53 * 54 * @since 1.0.0 55 */ priority()56 protected abstract int priority(); 57 58 /** 59 * Returns the scheme associated with the provider. The provider normally should only create a 60 * {@link NameResolver} when target URI scheme matches the provider scheme. It temporarily 61 * delegates to {@link Factory#getDefaultScheme()} before {@link NameResolver.Factory} is 62 * deprecated in https://github.com/grpc/grpc-java/issues/7133. 63 * 64 * <p>The scheme should be lower-case. 65 * 66 * @since 1.40.0 67 * */ getScheme()68 protected String getScheme() { 69 return getDefaultScheme(); 70 } 71 72 /** 73 * Returns the {@link SocketAddress} types this provider's name-resolver is capable of producing. 74 * This enables selection of the appropriate {@link ManagedChannelProvider} for a channel. 75 * 76 * @return the {@link SocketAddress} types this provider's name-resolver is capable of producing. 77 */ getProducedSocketAddressTypes()78 protected Collection<Class<? extends SocketAddress>> getProducedSocketAddressTypes() { 79 return Collections.singleton(InetSocketAddress.class); 80 } 81 } 82