Java tutorial
/** * 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.mapred; import java.io.EOFException; import java.io.FileDescriptor; import java.io.FileInputStream; import java.io.IOException; import java.io.InputStream; import org.apache.hadoop.conf.Configuration; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.fs.ChecksumException; import org.apache.hadoop.fs.HasFileDescriptor; import org.apache.hadoop.io.IOUtils; import org.apache.hadoop.io.ReadaheadPool; import org.apache.hadoop.io.ReadaheadPool.ReadaheadRequest; import org.apache.hadoop.mapreduce.MRConfig; import org.apache.hadoop.util.DataChecksum; /** * A checksum input stream, used for IFiles. * Used to validate the checksum of files created by {@link IFileOutputStream}. */ @InterfaceAudience.Private @InterfaceStability.Unstable public class IFileInputStream extends InputStream { private final InputStream in; //The input stream to be verified for checksum. private final FileDescriptor inFd; // the file descriptor, if it is known private final long length; //The total length of the input file private final long dataLength; private DataChecksum sum; private long currentOffset = 0; private final byte b[] = new byte[1]; private byte csum[] = null; private int checksumSize; private ReadaheadRequest curReadahead = null; private ReadaheadPool raPool = ReadaheadPool.getInstance(); private boolean readahead; private int readaheadLength; public static final Log LOG = LogFactory.getLog(IFileInputStream.class); private boolean disableChecksumValidation = false; /** * Create a checksum input stream that reads * @param in The input stream to be verified for checksum. * @param len The length of the input stream including checksum bytes. */ public IFileInputStream(InputStream in, long len, Configuration conf) { this.in = in; this.inFd = getFileDescriptorIfAvail(in); sum = DataChecksum.newDataChecksum(DataChecksum.Type.CRC32, Integer.MAX_VALUE); checksumSize = sum.getChecksumSize(); length = len; dataLength = length - checksumSize; conf = (conf != null) ? conf : new Configuration(); readahead = conf.getBoolean(MRConfig.MAPRED_IFILE_READAHEAD, MRConfig.DEFAULT_MAPRED_IFILE_READAHEAD); readaheadLength = conf.getInt(MRConfig.MAPRED_IFILE_READAHEAD_BYTES, MRConfig.DEFAULT_MAPRED_IFILE_READAHEAD_BYTES); doReadahead(); } private static FileDescriptor getFileDescriptorIfAvail(InputStream in) { FileDescriptor fd = null; try { if (in instanceof HasFileDescriptor) { fd = ((HasFileDescriptor) in).getFileDescriptor(); } else if (in instanceof FileInputStream) { fd = ((FileInputStream) in).getFD(); } } catch (IOException e) { LOG.info("Unable to determine FileDescriptor", e); } return fd; } /** * Close the input stream. Note that we need to read to the end of the * stream to validate the checksum. */ @Override public void close() throws IOException { if (curReadahead != null) { curReadahead.cancel(); } if (currentOffset < dataLength) { byte[] t = new byte[Math.min((int) (Integer.MAX_VALUE & (dataLength - currentOffset)), 32 * 1024)]; while (currentOffset < dataLength) { int n = read(t, 0, t.length); if (0 == n) { throw new EOFException("Could not validate checksum"); } } } in.close(); } @Override public long skip(long n) throws IOException { throw new IOException("Skip not supported for IFileInputStream"); } public long getPosition() { return (currentOffset >= dataLength) ? dataLength : currentOffset; } public long getSize() { return checksumSize; } /** * Read bytes from the stream. * At EOF, checksum is validated, but the checksum * bytes are not passed back in the buffer. */ public int read(byte[] b, int off, int len) throws IOException { if (currentOffset >= dataLength) { return -1; } doReadahead(); return doRead(b, off, len); } private void doReadahead() { if (raPool != null && inFd != null && readahead) { curReadahead = raPool.readaheadStream("ifile", inFd, currentOffset, readaheadLength, dataLength, curReadahead); } } /** * Read bytes from the stream. * At EOF, checksum is validated and sent back * as the last four bytes of the buffer. The caller should handle * these bytes appropriately */ public int readWithChecksum(byte[] b, int off, int len) throws IOException { if (currentOffset == length) { return -1; } else if (currentOffset >= dataLength) { // If the previous read drained off all the data, then just return // the checksum now. Note that checksum validation would have // happened in the earlier read int lenToCopy = (int) (checksumSize - (currentOffset - dataLength)); if (len < lenToCopy) { lenToCopy = len; } System.arraycopy(csum, (int) (currentOffset - dataLength), b, off, lenToCopy); currentOffset += lenToCopy; return lenToCopy; } int bytesRead = doRead(b, off, len); if (currentOffset == dataLength) { if (len >= bytesRead + checksumSize) { System.arraycopy(csum, 0, b, off + bytesRead, checksumSize); bytesRead += checksumSize; currentOffset += checksumSize; } } return bytesRead; } private int doRead(byte[] b, int off, int len) throws IOException { // If we are trying to read past the end of data, just read // the left over data if (currentOffset + len > dataLength) { len = (int) dataLength - (int) currentOffset; } int bytesRead = in.read(b, off, len); if (bytesRead < 0) { throw new ChecksumException("Checksum Error", 0); } sum.update(b, off, bytesRead); currentOffset += bytesRead; if (disableChecksumValidation) { return bytesRead; } if (currentOffset == dataLength) { // The last four bytes are checksum. Strip them and verify csum = new byte[checksumSize]; IOUtils.readFully(in, csum, 0, checksumSize); if (!sum.compare(csum, 0)) { throw new ChecksumException("Checksum Error", 0); } } return bytesRead; } @Override public int read() throws IOException { b[0] = 0; int l = read(b, 0, 1); if (l < 0) return l; // Upgrade the b[0] to an int so as not to misinterpret the // first bit of the byte as a sign bit int result = 0xFF & b[0]; return result; } public byte[] getChecksum() { return csum; } void disableChecksumValidation() { disableChecksumValidation = true; } }