hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/StreamCapabilitiesPolicy.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.fs;

import java.io.InputStream;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Static methods to implement policies for {@link StreamCapabilities}.
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class StreamCapabilitiesPolicy {
  public static final String CAN_UNBUFFER_NOT_IMPLEMENTED_MESSAGE =
          "claims unbuffer capabilty but does not implement CanUnbuffer";
  static final Logger LOG = LoggerFactory.getLogger(
          StreamCapabilitiesPolicy.class);
  /**
   * Implement the policy for {@link CanUnbuffer#unbuffer()}.
   *
   * @param in the input stream
   */
  public static void unbuffer(InputStream in) {
    try {
      if (in instanceof StreamCapabilities
          && ((StreamCapabilities) in).hasCapability(
          StreamCapabilities.UNBUFFER)) {
        ((CanUnbuffer) in).unbuffer();
      } else {
        LOG.debug(in.getClass().getName() + ":"
                + " does not implement StreamCapabilities"
                + " and the unbuffer capability");
      }
    } catch (ClassCastException e) {
      throw new UnsupportedOperationException(in.getClass().getName() + ": "
              + CAN_UNBUFFER_NOT_IMPLEMENTED_MESSAGE);
    }
  }
}