import org.apache.hadoop.hdfs.server.namenode.ha.WrappedFailoverProxyProvider; //导入依赖的package包/类
/** Creates the Failover proxy provider instance*/
@VisibleForTesting
public static <T> AbstractNNFailoverProxyProvider<T> createFailoverProxyProvider(
    Configuration conf, URI nameNodeUri, Class<T> xface, boolean checkPort,
    AtomicBoolean fallbackToSimpleAuth) throws IOException {
  Class<FailoverProxyProvider<T>> failoverProxyProviderClass = null;
  AbstractNNFailoverProxyProvider<T> providerNN;
  try {
    // Obtain the class of the proxy provider
    failoverProxyProviderClass = getFailoverProxyProviderClass(conf,
        nameNodeUri);
    if (failoverProxyProviderClass == null) {
      return null;
    }
    // Create a proxy provider instance.
    Constructor<FailoverProxyProvider<T>> ctor = failoverProxyProviderClass
        .getConstructor(Configuration.class, URI.class, Class.class);
    FailoverProxyProvider<T> provider = ctor.newInstance(conf, nameNodeUri,
        xface);

    // If the proxy provider is of an old implementation, wrap it.
    if (!(provider instanceof AbstractNNFailoverProxyProvider)) {
      providerNN = new WrappedFailoverProxyProvider<>(provider);
    } else {
      providerNN = (AbstractNNFailoverProxyProvider<T>)provider;
    }
  } catch (Exception e) {
    final String message = "Couldn't create proxy provider " +
        failoverProxyProviderClass;
    LOG.debug(message, e);
    if (e.getCause() instanceof IOException) {
      throw (IOException) e.getCause();
    } else {
      throw new IOException(message, e);
    }
  }

  // Check the port in the URI, if it is logical.
  if (checkPort && providerNN.useLogicalURI()) {
    int port = nameNodeUri.getPort();
    if (port > 0 &&
        port != HdfsClientConfigKeys.DFS_NAMENODE_RPC_PORT_DEFAULT) {
      // Throwing here without any cleanup is fine since we have not
      // actually created the underlying proxies yet.
      throw new IOException("Port " + port + " specified in URI "
          + nameNodeUri + " but host '" + nameNodeUri.getHost()
          + "' is a logical (HA) namenode"
          + " and does not use port information.");
    }
  }
  providerNN.setFallbackToSimpleAuth(fallbackToSimpleAuth);
  return providerNN;
}
 

import org.apache.hadoop.hdfs.server.namenode.ha.WrappedFailoverProxyProvider; //导入依赖的package包/类
/** Creates the Failover proxy provider instance*/
@VisibleForTesting
public static <T> AbstractNNFailoverProxyProvider<T> createFailoverProxyProvider(
    Configuration conf, URI nameNodeUri, Class<T> xface, boolean checkPort,
    AtomicBoolean fallbackToSimpleAuth) throws IOException {
  Class<FailoverProxyProvider<T>> failoverProxyProviderClass = null;
  AbstractNNFailoverProxyProvider<T> providerNN;
  Preconditions.checkArgument(
      xface.isAssignableFrom(NamenodeProtocols.class),
      "Interface %s is not a NameNode protocol", xface);
  try {
    // Obtain the class of the proxy provider
    failoverProxyProviderClass = getFailoverProxyProviderClass(conf,
        nameNodeUri);
    if (failoverProxyProviderClass == null) {
      return null;
    }
    // Create a proxy provider instance.
    Constructor<FailoverProxyProvider<T>> ctor = failoverProxyProviderClass
        .getConstructor(Configuration.class, URI.class, Class.class);
    FailoverProxyProvider<T> provider = ctor.newInstance(conf, nameNodeUri,
        xface);

    // If the proxy provider is of an old implementation, wrap it.
    if (!(provider instanceof AbstractNNFailoverProxyProvider)) {
      providerNN = new WrappedFailoverProxyProvider<T>(provider);
    } else {
      providerNN = (AbstractNNFailoverProxyProvider<T>)provider;
    }
  } catch (Exception e) {
    String message = "Couldn't create proxy provider " + failoverProxyProviderClass;
    if (LOG.isDebugEnabled()) {
      LOG.debug(message, e);
    }
    if (e.getCause() instanceof IOException) {
      throw (IOException) e.getCause();
    } else {
      throw new IOException(message, e);
    }
  }

  // Check the port in the URI, if it is logical.
  if (checkPort && providerNN.useLogicalURI()) {
    int port = nameNodeUri.getPort();
    if (port > 0 && port != NameNode.DEFAULT_PORT) {
      // Throwing here without any cleanup is fine since we have not
      // actually created the underlying proxies yet.
      throw new IOException("Port " + port + " specified in URI "
          + nameNodeUri + " but host '" + nameNodeUri.getHost()
          + "' is a logical (HA) namenode"
          + " and does not use port information.");
    }
  }
  providerNN.setFallbackToSimpleAuth(fallbackToSimpleAuth);
  return providerNN;
}