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/**
* 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.hdfs;
import java.io.IOException;
import java.nio.ByteBuffer;
/**
* Wraps different possible read implementations so that callers can be
* strategy-agnostic.
*/
interface ReaderStrategy {
/**
* Read from a block using the blockReader.
* @param blockReader
* @return number of bytes read
* @throws IOException
*/
int readFromBlock(BlockReader blockReader) throws IOException;
/**
* Read from a block using the blockReader with desired length to read.
* @param blockReader
* @param length number of bytes desired to read, not ensured
* @return number of bytes read
* @throws IOException
*/
int readFromBlock(BlockReader blockReader, int length) throws IOException;
/**
* Read or copy from a src buffer.
* @param src
* @return number of bytes copied
* Note: the position of the src buffer is not changed after the call
*/
int readFromBuffer(ByteBuffer src);
/**
* Read or copy length of data bytes from a src buffer with desired length.
* @param src
* @return number of bytes copied
* Note: the position of the src buffer is not changed after the call
*/
int readFromBuffer(ByteBuffer src, int length);
/**
* @return the target read buffer that reads data into.
*/
ByteBuffer getReadBuffer();
/**
* @return the target length to read.
*/
int getTargetLength();
}
/**
* Used to read bytes into a byte array buffer. Note it's not thread-safe
* and the behavior is not defined if concurrently operated.
*/
class ByteArrayStrategy implements ReaderStrategy {
private final DFSClient dfsClient;
private final ReadStatistics readStatistics;
private final byte[] readBuf;
private int offset;
private final int targetLength;
/**
* The constructor.
* @param readBuf target buffer to read into
* @param offset offset into the buffer
* @param targetLength target length of data
* @param readStatistics statistics counter
*/
public ByteArrayStrategy(byte[] readBuf, int offset, int targetLength,
ReadStatistics readStatistics,
DFSClient dfsClient) {
this.readBuf = readBuf;
this.offset = offset;
this.targetLength = targetLength;
this.readStatistics = readStatistics;
this.dfsClient = dfsClient;
}
@Override
public ByteBuffer getReadBuffer() {
return ByteBuffer.wrap(readBuf, offset, targetLength);
}
@Override
public int getTargetLength() {
return targetLength;
}
@Override
public int readFromBlock(BlockReader blockReader) throws IOException {
return readFromBlock(blockReader, targetLength);
}
@Override
public int readFromBlock(BlockReader blockReader,
int length) throws IOException {
int nRead = blockReader.read(readBuf, offset, length);
if (nRead > 0) {
offset += nRead;
}
return nRead;
}
@Override
public int readFromBuffer(ByteBuffer src) {
return readFromBuffer(src, src.remaining());
}
@Override
public int readFromBuffer(ByteBuffer src, int length) {
ByteBuffer dup = src.duplicate();
dup.get(readBuf, offset, length);
offset += length;
return length;
}
}
/**
* Used to read bytes into a user-supplied ByteBuffer. Note it's not thread-safe
* and the behavior is not defined if concurrently operated. When read operation
* is performed, the position of the underlying byte buffer will move forward as
* stated in ByteBufferReadable#read(ByteBuffer buf) method.
*/
class ByteBufferStrategy implements ReaderStrategy {
private final DFSClient dfsClient;
private final ReadStatistics readStatistics;
private final ByteBuffer readBuf;
private final int targetLength;
/**
* The constructor.
* @param readBuf target buffer to read into
* @param readStatistics statistics counter
*/
ByteBufferStrategy(ByteBuffer readBuf,
ReadStatistics readStatistics,
DFSClient dfsClient) {
this.readBuf = readBuf;
this.targetLength = readBuf.remaining();
this.readStatistics = readStatistics;
this.dfsClient = dfsClient;
}
@Override
public ByteBuffer getReadBuffer() {
return readBuf;
}
@Override
public int readFromBlock(BlockReader blockReader) throws IOException {
return readFromBlock(blockReader, readBuf.remaining());
}
@Override
public int readFromBlock(BlockReader blockReader,
int length) throws IOException {
ByteBuffer tmpBuf = readBuf.duplicate();
tmpBuf.limit(tmpBuf.position() + length);
int nRead = blockReader.read(tmpBuf);
// Only when data are read, update the position
if (nRead > 0) {
readBuf.position(readBuf.position() + nRead);
}
return nRead;
}
@Override
public int getTargetLength() {
return targetLength;
}
@Override
public int readFromBuffer(ByteBuffer src) {
return readFromBuffer(src, src.remaining());
}
@Override
public int readFromBuffer(ByteBuffer src, int length) {
ByteBuffer dup = src.duplicate();
int newLen = Math.min(readBuf.remaining(), dup.remaining());
newLen = Math.min(newLen, length);
dup.limit(dup.position() + newLen);
readBuf.put(dup);
return newLen;
}
}
