nl.topicus.jdbc.shaded.io.grpc.ManagedChannelProvider Maven / Gradle / Ivy
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/*
* 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 nl.topicus.jdbc.shaded.io.grpc;
import nl.topicus.jdbc.shaded.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.
*
* 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 {
private static final ManagedChannelProvider provider
= load(ManagedChannelProvider.class.getClassLoader());
@VisibleForTesting
static ManagedChannelProvider load(ClassLoader classLoader) {
Iterable candidates;
if (isAndroid()) {
candidates = getCandidatesViaHardCoded();
} else {
candidates = getCandidatesViaServiceLoader(classLoader);
}
List list = new ArrayList();
for (ManagedChannelProvider current : candidates) {
if (!current.isAvailable()) {
continue;
}
list.add(current);
}
if (list.isEmpty()) {
return null;
} else {
return Collections.max(list, new Comparator() {
@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 getCandidatesViaServiceLoader(
ClassLoader classLoader) {
Iterable i
= ServiceLoader.load(ManagedChannelProvider.class, classLoader);
// Attempt to load using the context class loader and ServiceLoader.
// This allows frameworks like http://aries.apache.org/modules/spi-fly.html to plug in.
if (!i.iterator().hasNext()) {
i = ServiceLoader.load(ManagedChannelProvider.class);
}
return i;
}
/**
* 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 getCandidatesViaHardCoded() {
// Class.forName(String) is used to remove the need for ProGuard configuration. Note that
// ProGuard does not detect usages of Class.forName(String, boolean, ClassLoader):
// https://sourceforge.net/p/proguard/bugs/418/
List list = new ArrayList();
try {
list.add(create(Class.forName("nl.topicus.jdbc.shaded.io.grpc.okhttp.OkHttpChannelProvider")));
} catch (ClassNotFoundException ex) {
// ignore
}
try {
list.add(create(Class.forName("nl.topicus.jdbc.shaded.io.grpc.netty.NettyChannelProvider")));
} 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 {
// Specify a class loader instead of null because we may be running under Robolectric
Class.forName("android.app.Application", /*initialize=*/ false,
ManagedChannelProvider.class.getClassLoader());
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);
}
}
}