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core: generifiy ServiceProvider class (grpc#3886)
Moving all the common code among different service provider classes to one place.
1 parent 417765b commit 2996207

10 files changed

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‎core/src/main/java/io/grpc/InternalServiceProviders.java‎

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/*
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* Copyright 2017, gRPC Authors All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc;
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import com.google.common.annotations.VisibleForTesting;
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import java.util.List;
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@Internal
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public final class InternalServiceProviders {
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private InternalServiceProviders() {
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}
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/**
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* Accessor for method.
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*/
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public static <T> T load(
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Class<T> klass,
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Iterable<Class<?>> hardcoded,
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ClassLoader classLoader,
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PriorityAccessor<T> priorityAccessor) {
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return ServiceProviders.load(klass, hardcoded, classLoader, priorityAccessor);
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}
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/**
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* Accessor for method.
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*/
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public static <T> List<T> loadAll(
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Class<T> klass,
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Iterable<Class<?>> hardCodedClasses,
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ClassLoader classLoader,
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PriorityAccessor<T> priorityAccessor) {
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return ServiceProviders.loadAll(klass, hardCodedClasses, classLoader, priorityAccessor);
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}
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/**
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* Accessor for method.
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*/
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@VisibleForTesting
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public static <T> Iterable<T> getCandidatesViaServiceLoader(Class<T> klass, ClassLoader cl) {
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return ServiceProviders.getCandidatesViaServiceLoader(klass, cl);
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}
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/**
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* Accessor for method.
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*/
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@VisibleForTesting
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public static <T> Iterable<T> getCandidatesViaHardCoded(
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Class<T> klass, Iterable<Class<?>> hardcoded) {
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return ServiceProviders.getCandidatesViaHardCoded(klass, hardcoded);
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}
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/**
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* Accessor for {@link ServiceProviders#isAndroid}.
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*/
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public static boolean isAndroid(ClassLoader cl) {
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return ServiceProviders.isAndroid(cl);
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}
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public interface PriorityAccessor<T> extends ServiceProviders.PriorityAccessor<T> {}
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}

‎core/src/main/java/io/grpc/ServiceProviders.java‎

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/*
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* Copyright 2017, gRPC Authors All rights reserved.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package io.grpc;
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import com.google.common.annotations.VisibleForTesting;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.List;
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import java.util.ServiceConfigurationError;
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import java.util.ServiceLoader;
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final class ServiceProviders {
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private ServiceProviders() {
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// do not instantiate
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}
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/**
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* If this is not Android, returns the highest priority implementation of the class via
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* {@link ServiceLoader}.
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* If this is Android, returns an instance of the highest priority class in {@code hardcoded}.
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*/
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public static <T> T load(
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Class<T> klass,
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Iterable<Class<?>> hardcoded,
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ClassLoader cl,
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PriorityAccessor<T> priorityAccessor) {
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List<T> candidates = loadAll(klass, hardcoded, cl, priorityAccessor);
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if (candidates.isEmpty()) {
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return null;
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}
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return candidates.get(0);
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}
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/**
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* If this is not Android, returns all available implementations discovered via
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* {@link ServiceLoader}.
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* If this is Android, returns all available implementations in {@code hardcoded}.
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* The list is sorted in descending priority order.
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*/
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public static <T> List<T> loadAll(
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Class<T> klass,
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Iterable<Class<?>> hardcoded,
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ClassLoader cl,
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final PriorityAccessor<T> priorityAccessor) {
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Iterable<T> candidates;
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if (isAndroid(cl)) {
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candidates = getCandidatesViaHardCoded(klass, hardcoded);
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} else {
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candidates = getCandidatesViaServiceLoader(klass, cl);
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}
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List<T> list = new ArrayList<T>();
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for (T current: candidates) {
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if (!priorityAccessor.isAvailable(current)) {
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continue;
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}
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list.add(current);
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}
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// Sort descending based on priority.
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Collections.sort(list, Collections.reverseOrder(new Comparator<T>() {
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@Override
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public int compare(T f1, T f2) {
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return priorityAccessor.getPriority(f1) - priorityAccessor.getPriority(f2);
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}
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}));
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return Collections.unmodifiableList(list);
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}
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/**
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* Returns true if the {@link ClassLoader} is for android.
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*/
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static boolean isAndroid(ClassLoader cl) {
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try {
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// Specify a class loader instead of null because we may be running under Robolectric
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Class.forName("android.app.Application", /*initialize=*/ false, cl);
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return true;
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} catch (Exception e) {
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// If Application isn't loaded, it might as well not be Android.
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return false;
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}
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}
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/**
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* Loads service providers for the {@code klass} service using {@link ServiceLoader}.
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*/
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@VisibleForTesting
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public static <T> Iterable<T> getCandidatesViaServiceLoader(Class<T> klass, ClassLoader cl) {
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Iterable<T> i = ServiceLoader.load(klass, cl);
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// Attempt to load using the context class loader and ServiceLoader.
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// This allows frameworks like http://aries.apache.org/modules/spi-fly.html to plug in.
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if (!i.iterator().hasNext()) {
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i = ServiceLoader.load(klass);
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}
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return i;
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}
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/**
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* Load providers from a hard-coded list. This avoids using getResource(), which has performance
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* problems on Android (see https://github.com/grpc/grpc-java/issues/2037).
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*/
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@VisibleForTesting
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static <T> Iterable<T> getCandidatesViaHardCoded(Class<T> klass, Iterable<Class<?>> hardcoded) {
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List<T> list = new ArrayList<T>();
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for (Class<?> candidate : hardcoded) {
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list.add(create(klass, candidate));
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}
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return list;
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}
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@VisibleForTesting
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static <T> T create(Class<T> klass, Class<?> rawClass) {
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try {
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return rawClass.asSubclass(klass).getConstructor().newInstance();
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} catch (Throwable t) {
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throw new ServiceConfigurationError(
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String.format("Provider %s could not be instantiated %s", rawClass.getName(), t), t);
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}
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}
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/**
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* An interface that allows us to get priority information about a provider.
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*/
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public interface PriorityAccessor<T> {
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/**
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* Checks this provider is available for use, taking the current environment into consideration.
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* If {@code false}, no other methods are safe to be called.
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*/
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boolean isAvailable(T provider);
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/**
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* A priority, from 0 to 10 that this provider should be used, taking the current environment
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* into consideration. 5 should be considered the default, and then tweaked based on environment
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* detection. A priority of 0 does not imply that the provider wouldn't work; just that it
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* should be last in line.
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*/
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int getPriority(T provider);
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}
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}

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