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

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package io.grpc;

import io.grpc.internal.ClientTransportFactory;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutorService;

import javax.annotation.Nullable;

/**
 * The base class for channel builders.
 *
 * @param <BuilderT> The concrete type of this builder.
 */
public abstract class AbstractChannelBuilder<BuilderT extends AbstractChannelBuilder<BuilderT>> {

  @Nullable
  private ExecutorService executor;
  private final List<ClientInterceptor> interceptors = new ArrayList<ClientInterceptor>();

  @Nullable
  private String userAgent;

  /**
   * Provides a custom executor.
   *
   * <p>It's an optional parameter. If the user has not provided an executor when the channel is
   * built, the builder will use a static cached thread pool.
   *
   * <p>The channel won't take ownership of the given executor. It's caller's responsibility to
   * shut down the executor when it's desired.
   */
  public final BuilderT executor(ExecutorService executor) {
    this.executor = executor;
    return thisT();
  }

  /**
   * Adds interceptors that will be called before the channel performs its real work. This is
   * functionally equivalent to using {@link ClientInterceptors#intercept(Channel, List)}, but while
   * still having access to the original {@code ChannelImpl}.
   */
  public final BuilderT intercept(List<ClientInterceptor> interceptors) {
    this.interceptors.addAll(interceptors);
    return thisT();
  }

  /**
   * Adds interceptors that will be called before the channel performs its real work. This is
   * functionally equivalent to using {@link ClientInterceptors#intercept(Channel,
   * ClientInterceptor...)}, but while still having access to the original {@code ChannelImpl}.
   */
  public final BuilderT intercept(ClientInterceptor... interceptors) {
    return intercept(Arrays.asList(interceptors));
  }

  private BuilderT thisT() {
    @SuppressWarnings("unchecked")
    BuilderT thisT = (BuilderT) this;
    return thisT;
  }

  /**
   * Provides a custom {@code User-Agent} for the application.
   *
   * <p>It's an optional parameter. If provided, the given agent will be prepended by the
   * grpc {@code User-Agent}.
   */
  @SuppressWarnings("unchecked")
  public final BuilderT userAgent(String userAgent) {
    this.userAgent = userAgent;
    return (BuilderT) this;
  }

  /**
   * Builds a channel using the given parameters.
   */
  public ChannelImpl build() {
    ClientTransportFactory transportFactory = buildTransportFactory();
    return new ChannelImpl(transportFactory, executor, userAgent, interceptors);
  }

  /**
   * Children of AbstractChannelBuilder should override this method to provide the
   * {@link ClientTransportFactory} appropriate for this channel.  This method is meant for
   * Transport implementors and should not be used by normal users.
   */
  @Internal
  protected abstract ClientTransportFactory buildTransportFactory();
}