import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.CachingStrategyProto; //导入依赖的package包/类
static private CachingStrategyProto getCachingStrategy(CachingStrategy cachingStrategy) {
  CachingStrategyProto.Builder builder = CachingStrategyProto.newBuilder();
  if (cachingStrategy.getReadahead() != null) {
    builder.setReadahead(cachingStrategy.getReadahead().longValue());
  }
  if (cachingStrategy.getDropBehind() != null) {
    builder.setDropBehind(cachingStrategy.getDropBehind().booleanValue());
  }
  return builder.build();
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.CachingStrategyProto; //导入依赖的package包/类
static private CachingStrategy getCachingStrategy(CachingStrategyProto strategy) {
  Boolean dropBehind = strategy.hasDropBehind() ?
      strategy.getDropBehind() : null;
  Long readahead = strategy.hasReadahead() ?
      strategy.getReadahead() : null;
  return new CachingStrategy(dropBehind, readahead);
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.CachingStrategyProto; //导入依赖的package包/类
static private CachingStrategyProto getCachingStrategy(
    CachingStrategy cachingStrategy) {
  CachingStrategyProto.Builder builder = CachingStrategyProto.newBuilder();
  if (cachingStrategy.getReadahead() != null) {
    builder.setReadahead(cachingStrategy.getReadahead());
  }
  if (cachingStrategy.getDropBehind() != null) {
    builder.setDropBehind(cachingStrategy.getDropBehind());
  }
  return builder.build();
}
 

import org.apache.hadoop.hdfs.protocol.proto.DataTransferProtos.CachingStrategyProto; //导入依赖的package包/类
private static List<Future<Channel>> connectToDataNodes(Configuration conf, DFSClient client,
    String clientName, LocatedBlock locatedBlock, long maxBytesRcvd, long latestGS,
    BlockConstructionStage stage, DataChecksum summer, EventLoopGroup eventLoopGroup,
    Class<? extends Channel> channelClass) {
  Enum<?>[] storageTypes = locatedBlock.getStorageTypes();
  DatanodeInfo[] datanodeInfos = locatedBlock.getLocations();
  boolean connectToDnViaHostname =
      conf.getBoolean(DFS_CLIENT_USE_DN_HOSTNAME, DFS_CLIENT_USE_DN_HOSTNAME_DEFAULT);
  int timeoutMs = conf.getInt(DFS_CLIENT_SOCKET_TIMEOUT_KEY, READ_TIMEOUT);
  ExtendedBlock blockCopy = new ExtendedBlock(locatedBlock.getBlock());
  blockCopy.setNumBytes(locatedBlock.getBlockSize());
  ClientOperationHeaderProto header = ClientOperationHeaderProto.newBuilder()
      .setBaseHeader(BaseHeaderProto.newBuilder().setBlock(PB_HELPER.convert(blockCopy))
          .setToken(PB_HELPER.convert(locatedBlock.getBlockToken())))
      .setClientName(clientName).build();
  ChecksumProto checksumProto = DataTransferProtoUtil.toProto(summer);
  OpWriteBlockProto.Builder writeBlockProtoBuilder = OpWriteBlockProto.newBuilder()
      .setHeader(header).setStage(OpWriteBlockProto.BlockConstructionStage.valueOf(stage.name()))
      .setPipelineSize(1).setMinBytesRcvd(locatedBlock.getBlock().getNumBytes())
      .setMaxBytesRcvd(maxBytesRcvd).setLatestGenerationStamp(latestGS)
      .setRequestedChecksum(checksumProto)
      .setCachingStrategy(CachingStrategyProto.newBuilder().setDropBehind(true).build());
  List<Future<Channel>> futureList = new ArrayList<>(datanodeInfos.length);
  for (int i = 0; i < datanodeInfos.length; i++) {
    DatanodeInfo dnInfo = datanodeInfos[i];
    Enum<?> storageType = storageTypes[i];
    Promise<Channel> promise = eventLoopGroup.next().newPromise();
    futureList.add(promise);
    String dnAddr = dnInfo.getXferAddr(connectToDnViaHostname);
    new Bootstrap().group(eventLoopGroup).channel(channelClass)
        .option(CONNECT_TIMEOUT_MILLIS, timeoutMs).handler(new ChannelInitializer<Channel>() {

          @Override
          protected void initChannel(Channel ch) throws Exception {
            // we need to get the remote address of the channel so we can only move on after
            // channel connected. Leave an empty implementation here because netty does not allow
            // a null handler.
          }
        }).connect(NetUtils.createSocketAddr(dnAddr)).addListener(new ChannelFutureListener() {

          @Override
          public void operationComplete(ChannelFuture future) throws Exception {
            if (future.isSuccess()) {
              initialize(conf, future.channel(), dnInfo, storageType, writeBlockProtoBuilder,
                timeoutMs, client, locatedBlock.getBlockToken(), promise);
            } else {
              promise.tryFailure(future.cause());
            }
          }
        });
  }
  return futureList;
}