org.apache.hadoop.fs.ByteBufferPositionedReadable Maven / Gradle / Ivy
/**
* 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.EOFException;
import java.io.IOException;
import java.nio.ByteBuffer;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
/**
* Implementers of this interface provide a positioned read API that writes to a
* {@link ByteBuffer} rather than a {@code byte[]}.
*
* @see PositionedReadable
* @see ByteBufferReadable
*/
@InterfaceAudience.Public
@InterfaceStability.Evolving
public interface ByteBufferPositionedReadable {
/**
* Reads up to {@code buf.remaining()} bytes into buf from a given position
* in the file and returns the number of bytes read. Callers should use
* {@code buf.limit(...)} to control the size of the desired read and
* {@code buf.position(...)} to control the offset into the buffer the data
* should be written to.
*
* After a successful call, {@code buf.position()} will be advanced by the
* number of bytes read and {@code buf.limit()} will be unchanged.
*
* In the case of an exception, the state of the buffer (the contents of the
* buffer, the {@code buf.position()}, the {@code buf.limit()}, etc.) is
* undefined, and callers should be prepared to recover from this
* eventuality.
*
* Callers should use {@link StreamCapabilities#hasCapability(String)} with
* {@link StreamCapabilities#PREADBYTEBUFFER} to check if the underlying
* stream supports this interface, otherwise they might get a
* {@link UnsupportedOperationException}.
*
* Implementations should treat 0-length requests as legitimate, and must not
* signal an error upon their receipt.
*
* This does not change the current offset of a file, and is thread-safe.
*
* @param position position within file
* @param buf the ByteBuffer to receive the results of the read operation.
* @return the number of bytes read, possibly zero, or -1 if reached
* end-of-stream
* @throws IOException if there is some error performing the read
*/
int read(long position, ByteBuffer buf) throws IOException;
/**
* Reads {@code buf.remaining()} bytes into buf from a given position in
* the file or until the end of the data was reached before the read
* operation completed. Callers should use {@code buf.limit(...)} to
* control the size of the desired read and {@code buf.position(...)} to
* control the offset into the buffer the data should be written to.
*
* This operation provides similar semantics to
* {@link #read(long, ByteBuffer)}, the difference is that this method is
* guaranteed to read data until the {@link ByteBuffer} is full, or until
* the end of the data stream is reached.
*
* @param position position within file
* @param buf the ByteBuffer to receive the results of the read operation.
* @throws IOException if there is some error performing the read
* @throws EOFException the end of the data was reached before
* the read operation completed
* @see #read(long, ByteBuffer)
*/
void readFully(long position, ByteBuffer buf) throws IOException;
}