nl.topicus.jdbc.shaded.io.grpc.ServerProvider 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 nl.topicus.jdbc.shaded.io.grpc.ManagedChannelProvider.ProviderNotFoundException;
import java.util.ServiceLoader;
/**
* Provider of servers 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 ServerProvider {
private static final ServerProvider provider =
load(ServerProvider.class.getClassLoader());
@VisibleForTesting
static final ServerProvider load(ClassLoader cl) {
ServiceLoader providers = ServiceLoader.load(ServerProvider.class, cl);
// 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 (!providers.iterator().hasNext()) {
providers = ServiceLoader.load(ServerProvider.class);
}
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);
}