001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.fs;
019    
020    import java.io.IOException;
021    import java.nio.ByteBuffer;
022    
023    /**
024     * Implementers of this interface provide a read API that writes to a
025     * ByteBuffer, not a byte[].
026     */
027    public interface ByteBufferReadable {
028      /**
029       * Reads up to buf.remaining() bytes into buf. Callers should use
030       * buf.limit(..) to control the size of the desired read.
031       * <p/>
032       * After a successful call, buf.position() and buf.limit() should be
033       * unchanged, and therefore any data can be immediately read from buf.
034       * buf.mark() may be cleared or updated.
035       * <p/>
036       * In the case of an exception, the values of buf.position() and buf.limit()
037       * are undefined, and callers should be prepared to recover from this
038       * eventuality.
039       * <p/>
040       * Many implementations will throw {@link UnsupportedOperationException}, so
041       * callers that are not confident in support for this method from the
042       * underlying filesystem should be prepared to handle that exception.
043       * <p/>
044       * Implementations should treat 0-length requests as legitimate, and must not
045       * signal an error upon their receipt.
046       *
047       * @param buf
048       *          the ByteBuffer to receive the results of the read operation. Up to
049       *          buf.limit() - buf.position() bytes may be read.
050       * @return the number of bytes available to read from buf
051       * @throws IOException
052       *           if there is some error performing the read
053       */
054      public int read(ByteBuffer buf) throws IOException;
055    }