1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.hadoop.mapreduce.lib.input; 20 21 import org.apache.hadoop.classification.InterfaceAudience; 22 import org.apache.hadoop.classification.InterfaceStability; 23 import org.apache.hadoop.fs.Path; 24 import org.apache.hadoop.io.LongWritable; 25 import org.apache.hadoop.io.Text; 26 import org.apache.hadoop.io.compress.CompressionCodec; 27 import org.apache.hadoop.io.compress.CompressionCodecFactory; 28 import org.apache.hadoop.io.compress.SplittableCompressionCodec; 29 import org.apache.hadoop.mapreduce.InputFormat; 30 import org.apache.hadoop.mapreduce.InputSplit; 31 import org.apache.hadoop.mapreduce.JobContext; 32 import org.apache.hadoop.mapreduce.RecordReader; 33 import org.apache.hadoop.mapreduce.TaskAttemptContext; 34 35 import com.google.common.base.Charsets; 36 37 /** An {@link InputFormat} for plain text files. Files are broken into lines. 38 * Either linefeed or carriage-return are used to signal end of line. Keys are 39 * the position in the file, and values are the line of text.. */ 40 @InterfaceAudience.Public 41 @InterfaceStability.Stable 42 public class TextInputFormat extends FileInputFormat<LongWritable, Text> { 43 44 @Override 45 public RecordReader<LongWritable, Text> 46 createRecordReader(InputSplit split, 47 TaskAttemptContext context) { 48 String delimiter = context.getConfiguration().get( 49 "textinputformat.record.delimiter"); 50 byte[] recordDelimiterBytes = null; 51 if (null != delimiter) 52 recordDelimiterBytes = delimiter.getBytes(Charsets.UTF_8); 53 return new LineRecordReader(recordDelimiterBytes); 54 } 55 56 @Override 57 protected boolean isSplitable(JobContext context, Path file) { 58 final CompressionCodec codec = 59 new CompressionCodecFactory(context.getConfiguration()).getCodec(file); 60 if (null == codec) { 61 return true; 62 } 63 return codec instanceof SplittableCompressionCodec; 64 } 65 66 }
TextInputFormat
父类(TextInputFormat本身含义为把每一行解析成键值对)
1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.hadoop.mapreduce.lib.input; 20 21 import java.io.IOException; 22 import java.util.ArrayList; 23 import java.util.List; 24 25 import org.apache.commons.logging.Log; 26 import org.apache.commons.logging.LogFactory; 27 import org.apache.hadoop.classification.InterfaceAudience; 28 import org.apache.hadoop.classification.InterfaceStability; 29 import org.apache.hadoop.conf.Configuration; 30 import org.apache.hadoop.fs.FileStatus; 31 import org.apache.hadoop.fs.FileSystem; 32 import org.apache.hadoop.fs.LocatedFileStatus; 33 import org.apache.hadoop.fs.Path; 34 import org.apache.hadoop.fs.PathFilter; 35 import org.apache.hadoop.fs.BlockLocation; 36 import org.apache.hadoop.fs.RemoteIterator; 37 import org.apache.hadoop.mapred.LocatedFileStatusFetcher; 38 import org.apache.hadoop.mapred.SplitLocationInfo; 39 import org.apache.hadoop.mapreduce.InputFormat; 40 import org.apache.hadoop.mapreduce.InputSplit; 41 import org.apache.hadoop.mapreduce.Job; 42 import org.apache.hadoop.mapreduce.JobContext; 43 import org.apache.hadoop.mapreduce.Mapper; 44 import org.apache.hadoop.mapreduce.security.TokenCache; 45 import org.apache.hadoop.util.ReflectionUtils; 46 import org.apache.hadoop.util.StringUtils; 47 48 import com.google.common.base.Stopwatch; 49 import com.google.common.collect.Lists; 50 51 /** 52 * A base class for file-based {@link InputFormat}s. 53 * 54 * <p><code>FileInputFormat</code> is the base class for all file-based 55 * <code>InputFormat</code>s. This provides a generic implementation of 56 * {@link #getSplits(JobContext)}. 57 * Subclasses of <code>FileInputFormat</code> can also override the 58 * {@link #isSplitable(JobContext, Path)} method to ensure input-files are 59 * not split-up and are processed as a whole by {@link Mapper}s. 60 */ 61 @InterfaceAudience.Public 62 @InterfaceStability.Stable 63 public abstract class FileInputFormat<K, V> extends InputFormat<K, V> { 64 public static final String INPUT_DIR = 65 "mapreduce.input.fileinputformat.inputdir"; 66 public static final String SPLIT_MAXSIZE = 67 "mapreduce.input.fileinputformat.split.maxsize"; 68 public static final String SPLIT_MINSIZE = 69 "mapreduce.input.fileinputformat.split.minsize"; 70 public static final String PATHFILTER_CLASS = 71 "mapreduce.input.pathFilter.class"; 72 public static final String NUM_INPUT_FILES = 73 "mapreduce.input.fileinputformat.numinputfiles"; 74 public static final String INPUT_DIR_RECURSIVE = 75 "mapreduce.input.fileinputformat.input.dir.recursive"; 76 public static final String LIST_STATUS_NUM_THREADS = 77 "mapreduce.input.fileinputformat.list-status.num-threads"; 78 public static final int DEFAULT_LIST_STATUS_NUM_THREADS = 1; 79 80 private static final Log LOG = LogFactory.getLog(FileInputFormat.class); 81 82 private static final double SPLIT_SLOP = 1.1; // 10% slop 83 84 @Deprecated 85 public static enum Counter { 86 BYTES_READ 87 } 88 89 private static final PathFilter hiddenFileFilter = new PathFilter(){ 90 public boolean accept(Path p){ 91 String name = p.getName(); 92 return !name.startsWith("_") && !name.startsWith("."); 93 } 94 }; 95 96 /** 97 * Proxy PathFilter that accepts a path only if all filters given in the 98 * constructor do. Used by the listPaths() to apply the built-in 99 * hiddenFileFilter together with a user provided one (if any). 100 */ 101 private static class MultiPathFilter implements PathFilter { 102 private List<PathFilter> filters; 103 104 public MultiPathFilter(List<PathFilter> filters) { 105 this.filters = filters; 106 } 107 108 public boolean accept(Path path) { 109 for (PathFilter filter : filters) { 110 if (!filter.accept(path)) { 111 return false; 112 } 113 } 114 return true; 115 } 116 } 117 118 /** 119 * @param job 120 * the job to modify 121 * @param inputDirRecursive 122 */ 123 public static void setInputDirRecursive(Job job, 124 boolean inputDirRecursive) { 125 job.getConfiguration().setBoolean(INPUT_DIR_RECURSIVE, 126 inputDirRecursive); 127 } 128 129 /** 130 * @param job 131 * the job to look at. 132 * @return should the files to be read recursively? 133 */ 134 public static boolean getInputDirRecursive(JobContext job) { 135 return job.getConfiguration().getBoolean(INPUT_DIR_RECURSIVE, 136 false); 137 } 138 139 /** 140 * Get the lower bound on split size imposed by the format. 141 * @return the number of bytes of the minimal split for this format 142 */ 143 protected long getFormatMinSplitSize() { 144 return 1; 145 } 146 147 /** 148 * Is the given filename splitable? Usually, true, but if the file is 149 * stream compressed, it will not be. 150 * 151 * <code>FileInputFormat</code> implementations can override this and return 152 * <code>false</code> to ensure that individual input files are never split-up 153 * so that {@link Mapper}s process entire files. 154 * 155 * @param context the job context 156 * @param filename the file name to check 157 * @return is this file splitable? 158 */ 159 protected boolean isSplitable(JobContext context, Path filename) { 160 return true; 161 } 162 163 /** 164 * Set a PathFilter to be applied to the input paths for the map-reduce job. 165 * @param job the job to modify 166 * @param filter the PathFilter class use for filtering the input paths. 167 */ 168 public static void setInputPathFilter(Job job, 169 Class<? extends PathFilter> filter) { 170 job.getConfiguration().setClass(PATHFILTER_CLASS, filter, 171 PathFilter.class); 172 } 173 174 /** 175 * Set the minimum input split size 176 * @param job the job to modify 177 * @param size the minimum size 178 */ 179 public static void setMinInputSplitSize(Job job, 180 long size) { 181 job.getConfiguration().setLong(SPLIT_MINSIZE, size); 182 } 183 184 /** 185 * Get the minimum split size 186 * @param job the job 187 * @return the minimum number of bytes that can be in a split 188 */ 189 public static long getMinSplitSize(JobContext job) { 190 return job.getConfiguration().getLong(SPLIT_MINSIZE, 1L); 191 } 192 193 /** 194 * Set the maximum split size 195 * @param job the job to modify 196 * @param size the maximum split size 197 */ 198 public static void setMaxInputSplitSize(Job job, 199 long size) { 200 job.getConfiguration().setLong(SPLIT_MAXSIZE, size); 201 } 202 203 /** 204 * Get the maximum split size. 205 * @param context the job to look at. 206 * @return the maximum number of bytes a split can include 207 */ 208 public static long getMaxSplitSize(JobContext context) { 209 return context.getConfiguration().getLong(SPLIT_MAXSIZE, 210 Long.MAX_VALUE); 211 } 212 213 /** 214 * Get a PathFilter instance of the filter set for the input paths. 215 * 216 * @return the PathFilter instance set for the job, NULL if none has been set. 217 */ 218 public static PathFilter getInputPathFilter(JobContext context) { 219 Configuration conf = context.getConfiguration(); 220 Class<?> filterClass = conf.getClass(PATHFILTER_CLASS, null, 221 PathFilter.class); 222 return (filterClass != null) ? 223 (PathFilter) ReflectionUtils.newInstance(filterClass, conf) : null; 224 } 225 226 /** List input directories. 227 * Subclasses may override to, e.g., select only files matching a regular 228 * expression. 229 * 230 * @param job the job to list input paths for 231 * @return array of FileStatus objects 232 * @throws IOException if zero items. 233 */ 234 protected List<FileStatus> listStatus(JobContext job 235 ) throws IOException { 236 Path[] dirs = getInputPaths(job); 237 if (dirs.length == 0) { 238 throw new IOException("No input paths specified in job"); 239 } 240 241 // get tokens for all the required FileSystems.. 242 TokenCache.obtainTokensForNamenodes(job.getCredentials(), dirs, 243 job.getConfiguration()); 244 245 // Whether we need to recursive look into the directory structure 246 boolean recursive = getInputDirRecursive(job); 247 248 // creates a MultiPathFilter with the hiddenFileFilter and the 249 // user provided one (if any). 250 List<PathFilter> filters = new ArrayList<PathFilter>(); 251 filters.add(hiddenFileFilter); 252 PathFilter jobFilter = getInputPathFilter(job); 253 if (jobFilter != null) { 254 filters.add(jobFilter); 255 } 256 PathFilter inputFilter = new MultiPathFilter(filters); 257 258 List<FileStatus> result = null; 259 260 int numThreads = job.getConfiguration().getInt(LIST_STATUS_NUM_THREADS, 261 DEFAULT_LIST_STATUS_NUM_THREADS); 262 Stopwatch sw = new Stopwatch().start(); 263 if (numThreads == 1) { 264 result = singleThreadedListStatus(job, dirs, inputFilter, recursive); 265 } else { 266 Iterable<FileStatus> locatedFiles = null; 267 try { 268 LocatedFileStatusFetcher locatedFileStatusFetcher = new LocatedFileStatusFetcher( 269 job.getConfiguration(), dirs, recursive, inputFilter, true); 270 locatedFiles = locatedFileStatusFetcher.getFileStatuses(); 271 } catch (InterruptedException e) { 272 throw new IOException("Interrupted while getting file statuses"); 273 } 274 result = Lists.newArrayList(locatedFiles); 275 } 276 277 sw.stop(); 278 if (LOG.isDebugEnabled()) { 279 LOG.debug("Time taken to get FileStatuses: " + sw.elapsedMillis()); 280 } 281 LOG.info("Total input paths to process : " + result.size()); 282 return result; 283 } 284 285 private List<FileStatus> singleThreadedListStatus(JobContext job, Path[] dirs, 286 PathFilter inputFilter, boolean recursive) throws IOException { 287 List<FileStatus> result = new ArrayList<FileStatus>(); 288 List<IOException> errors = new ArrayList<IOException>(); 289 for (int i=0; i < dirs.length; ++i) { 290 Path p = dirs[i]; 291 FileSystem fs = p.getFileSystem(job.getConfiguration()); 292 FileStatus[] matches = fs.globStatus(p, inputFilter); 293 if (matches == null) { 294 errors.add(new IOException("Input path does not exist: " + p)); 295 } else if (matches.length == 0) { 296 errors.add(new IOException("Input Pattern " + p + " matches 0 files")); 297 } else { 298 for (FileStatus globStat: matches) { 299 if (globStat.isDirectory()) { 300 RemoteIterator<LocatedFileStatus> iter = 301 fs.listLocatedStatus(globStat.getPath()); 302 while (iter.hasNext()) { 303 LocatedFileStatus stat = iter.next(); 304 if (inputFilter.accept(stat.getPath())) { 305 if (recursive && stat.isDirectory()) { 306 addInputPathRecursively(result, fs, stat.getPath(), 307 inputFilter); 308 } else { 309 result.add(stat); 310 } 311 } 312 } 313 } else { 314 result.add(globStat); 315 } 316 } 317 } 318 } 319 320 if (!errors.isEmpty()) { 321 throw new InvalidInputException(errors); 322 } 323 return result; 324 } 325 326 /** 327 * Add files in the input path recursively into the results. 328 * @param result 329 * The List to store all files. 330 * @param fs 331 * The FileSystem. 332 * @param path 333 * The input path. 334 * @param inputFilter 335 * The input filter that can be used to filter files/dirs. 336 * @throws IOException 337 */ 338 protected void addInputPathRecursively(List<FileStatus> result, 339 FileSystem fs, Path path, PathFilter inputFilter) 340 throws IOException { 341 RemoteIterator<LocatedFileStatus> iter = fs.listLocatedStatus(path); 342 while (iter.hasNext()) { 343 LocatedFileStatus stat = iter.next(); 344 if (inputFilter.accept(stat.getPath())) { 345 if (stat.isDirectory()) { 346 addInputPathRecursively(result, fs, stat.getPath(), inputFilter); 347 } else { 348 result.add(stat); 349 } 350 } 351 } 352 } 353 354 355 /** 356 * A factory that makes the split for this class. It can be overridden 357 * by sub-classes to make sub-types 358 */ 359 protected FileSplit makeSplit(Path file, long start, long length, 360 String[] hosts) { 361 return new FileSplit(file, start, length, hosts); 362 } 363 364 /** 365 * A factory that makes the split for this class. It can be overridden 366 * by sub-classes to make sub-types 367 */ 368 protected FileSplit makeSplit(Path file, long start, long length, 369 String[] hosts, String[] inMemoryHosts) { 370 return new FileSplit(file, start, length, hosts, inMemoryHosts); 371 } 372 373 /** 374 * Generate the list of files and make them into FileSplits. 375 * @param job the job context 376 * @throws IOException 377 */ 378 public List<InputSplit> getSplits(JobContext job) throws IOException { 379 Stopwatch sw = new Stopwatch().start(); 380 long minSize = Math.max(getFormatMinSplitSize(), getMinSplitSize(job)); 381 long maxSize = getMaxSplitSize(job); 382 383 // generate splits 384 List<InputSplit> splits = new ArrayList<InputSplit>(); 385 List<FileStatus> files = listStatus(job); 386 for (FileStatus file: files) { 387 Path path = file.getPath(); 388 long length = file.getLen(); 389 if (length != 0) { 390 BlockLocation[] blkLocations; 391 if (file instanceof LocatedFileStatus) { 392 blkLocations = ((LocatedFileStatus) file).getBlockLocations(); 393 } else { 394 FileSystem fs = path.getFileSystem(job.getConfiguration()); 395 blkLocations = fs.getFileBlockLocations(file, 0, length); 396 } 397 if (isSplitable(job, path)) { 398 long blockSize = file.getBlockSize(); 399 long splitSize = computeSplitSize(blockSize, minSize, maxSize); 400 401 long bytesRemaining = length; 402 while (((double) bytesRemaining)/splitSize > SPLIT_SLOP) { 403 int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining); 404 splits.add(makeSplit(path, length-bytesRemaining, splitSize, 405 blkLocations[blkIndex].getHosts(), 406 blkLocations[blkIndex].getCachedHosts())); 407 bytesRemaining -= splitSize; 408 } 409 410 if (bytesRemaining != 0) { 411 int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining); 412 splits.add(makeSplit(path, length-bytesRemaining, bytesRemaining, 413 blkLocations[blkIndex].getHosts(), 414 blkLocations[blkIndex].getCachedHosts())); 415 } 416 } else { // not splitable 417 splits.add(makeSplit(path, 0, length, blkLocations[0].getHosts(), 418 blkLocations[0].getCachedHosts())); 419 } 420 } else { 421 //Create empty hosts array for zero length files 422 splits.add(makeSplit(path, 0, length, new String[0])); 423 } 424 } 425 // Save the number of input files for metrics/loadgen 426 job.getConfiguration().setLong(NUM_INPUT_FILES, files.size()); 427 sw.stop(); 428 if (LOG.isDebugEnabled()) { 429 LOG.debug("Total # of splits generated by getSplits: " + splits.size() 430 + ", TimeTaken: " + sw.elapsedMillis()); 431 } 432 return splits; 433 } 434 435 protected long computeSplitSize(long blockSize, long minSize, 436 long maxSize) { 437 return Math.max(minSize, Math.min(maxSize, blockSize)); 438 } 439 440 protected int getBlockIndex(BlockLocation[] blkLocations, 441 long offset) { 442 for (int i = 0 ; i < blkLocations.length; i++) { 443 // is the offset inside this block? 444 if ((blkLocations[i].getOffset() <= offset) && 445 (offset < blkLocations[i].getOffset() + blkLocations[i].getLength())){ 446 return i; 447 } 448 } 449 BlockLocation last = blkLocations[blkLocations.length -1]; 450 long fileLength = last.getOffset() + last.getLength() -1; 451 throw new IllegalArgumentException("Offset " + offset + 452 " is outside of file (0.." + 453 fileLength + ")"); 454 } 455 456 /** 457 * Sets the given comma separated paths as the list of inputs 458 * for the map-reduce job. 459 * 460 * @param job the job 461 * @param commaSeparatedPaths Comma separated paths to be set as 462 * the list of inputs for the map-reduce job. 463 */ 464 public static void setInputPaths(Job job, 465 String commaSeparatedPaths 466 ) throws IOException { 467 setInputPaths(job, StringUtils.stringToPath( 468 getPathStrings(commaSeparatedPaths))); 469 } 470 471 /** 472 * Add the given comma separated paths to the list of inputs for 473 * the map-reduce job. 474 * 475 * @param job The job to modify 476 * @param commaSeparatedPaths Comma separated paths to be added to 477 * the list of inputs for the map-reduce job. 478 */ 479 public static void addInputPaths(Job job, 480 String commaSeparatedPaths 481 ) throws IOException { 482 for (String str : getPathStrings(commaSeparatedPaths)) { 483 addInputPath(job, new Path(str)); 484 } 485 } 486 487 /** 488 * Set the array of {@link Path}s as the list of inputs 489 * for the map-reduce job. 490 * 491 * @param job The job to modify 492 * @param inputPaths the {@link Path}s of the input directories/files 493 * for the map-reduce job. 494 */ 495 public static void setInputPaths(Job job, 496 Path... inputPaths) throws IOException { 497 Configuration conf = job.getConfiguration(); 498 Path path = inputPaths[0].getFileSystem(conf).makeQualified(inputPaths[0]); 499 StringBuffer str = new StringBuffer(StringUtils.escapeString(path.toString())); 500 for(int i = 1; i < inputPaths.length;i++) { 501 str.append(StringUtils.COMMA_STR); 502 path = inputPaths[i].getFileSystem(conf).makeQualified(inputPaths[i]); 503 str.append(StringUtils.escapeString(path.toString())); 504 } 505 conf.set(INPUT_DIR, str.toString()); 506 } 507 508 /** 509 * Add a {@link Path} to the list of inputs for the map-reduce job. 510 * 511 * @param job The {@link Job} to modify 512 * @param path {@link Path} to be added to the list of inputs for 513 * the map-reduce job. 514 */ 515 public static void addInputPath(Job job, 516 Path path) throws IOException { 517 Configuration conf = job.getConfiguration(); 518 path = path.getFileSystem(conf).makeQualified(path); 519 String dirStr = StringUtils.escapeString(path.toString()); 520 String dirs = conf.get(INPUT_DIR); 521 conf.set(INPUT_DIR, dirs == null ? dirStr : dirs + "," + dirStr); 522 } 523 524 // This method escapes commas in the glob pattern of the given paths. 525 private static String[] getPathStrings(String commaSeparatedPaths) { 526 int length = commaSeparatedPaths.length(); 527 int curlyOpen = 0; 528 int pathStart = 0; 529 boolean globPattern = false; 530 List<String> pathStrings = new ArrayList<String>(); 531 532 for (int i=0; i<length; i++) { 533 char ch = commaSeparatedPaths.charAt(i); 534 switch(ch) { 535 case '{' : { 536 curlyOpen++; 537 if (!globPattern) { 538 globPattern = true; 539 } 540 break; 541 } 542 case '}' : { 543 curlyOpen--; 544 if (curlyOpen == 0 && globPattern) { 545 globPattern = false; 546 } 547 break; 548 } 549 case ',' : { 550 if (!globPattern) { 551 pathStrings.add(commaSeparatedPaths.substring(pathStart, i)); 552 pathStart = i + 1 ; 553 } 554 break; 555 } 556 default: 557 continue; // nothing special to do for this character 558 } 559 } 560 pathStrings.add(commaSeparatedPaths.substring(pathStart, length)); 561 562 return pathStrings.toArray(new String[0]); 563 } 564 565 /** 566 * Get the list of input {@link Path}s for the map-reduce job. 567 * 568 * @param context The job 569 * @return the list of input {@link Path}s for the map-reduce job. 570 */ 571 public static Path[] getInputPaths(JobContext context) { 572 String dirs = context.getConfiguration().get(INPUT_DIR, ""); 573 String [] list = StringUtils.split(dirs); 574 Path[] result = new Path[list.length]; 575 for (int i = 0; i < list.length; i++) { 576 result[i] = new Path(StringUtils.unEscapeString(list[i])); 577 } 578 return result; 579 } 580 581 }
FileInputFormat
父类
1 /** 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 package org.apache.hadoop.mapreduce; 20 21 import java.io.IOException; 22 import java.util.List; 23 24 import org.apache.hadoop.classification.InterfaceAudience; 25 import org.apache.hadoop.classification.InterfaceStability; 26 import org.apache.hadoop.fs.FileSystem; 27 import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; 28 29 /** 30 * <code>InputFormat</code> describes the input-specification for a 31 * Map-Reduce job. 32 * 33 * <p>The Map-Reduce framework relies on the <code>InputFormat</code> of the 34 * job to:<p> 35 * <ol> 36 * <li> 37 * Validate the input-specification of the job. 38 * <li> 39 * Split-up the input file(s) into logical {@link InputSplit}s, each of 40 * which is then assigned to an individual {@link Mapper}. 41 * </li> 42 * <li> 43 * Provide the {@link RecordReader} implementation to be used to glean 44 * input records from the logical <code>InputSplit</code> for processing by 45 * the {@link Mapper}. 46 * </li> 47 * </ol> 48 * 49 * <p>The default behavior of file-based {@link InputFormat}s, typically 50 * sub-classes of {@link FileInputFormat}, is to split the 51 * input into <i>logical</i> {@link InputSplit}s based on the total size, in 52 * bytes, of the input files. However, the {@link FileSystem} blocksize of 53 * the input files is treated as an upper bound for input splits. A lower bound 54 * on the split size can be set via 55 * <a href="{@docRoot}/../hadoop-mapreduce-client/hadoop-mapreduce-client-core/mapred-default.xml#mapreduce.input.fileinputformat.split.minsize"> 56 * mapreduce.input.fileinputformat.split.minsize</a>.</p> 57 * 58 * <p>Clearly, logical splits based on input-size is insufficient for many 59 * applications since record boundaries are to respected. In such cases, the 60 * application has to also implement a {@link RecordReader} on whom lies the 61 * responsibility to respect record-boundaries and present a record-oriented 62 * view of the logical <code>InputSplit</code> to the individual task. 63 * 64 * @see InputSplit 65 * @see RecordReader 66 * @see FileInputFormat 67 */ 68 @InterfaceAudience.Public 69 @InterfaceStability.Stable 70 public abstract class InputFormat<K, V> { 71 72 /** 73 * Logically split the set of input files for the job. 74 * 75 * <p>Each {@link InputSplit} is then assigned to an individual {@link Mapper} 76 * for processing.</p> 77 * 78 * <p><i>Note</i>: The split is a <i>logical</i> split of the inputs and the 79 * input files are not physically split into chunks. For e.g. a split could 80 * be <i><input-file-path, start, offset></i> tuple. The InputFormat 81 * also creates the {@link RecordReader} to read the {@link InputSplit}. 82 * 83 * @param context job configuration. 84 * @return an array of {@link InputSplit}s for the job. 85 */ 86 public abstract 87 List<InputSplit> getSplits(JobContext context 88 ) throws IOException, InterruptedException; 89 90 /** 91 * Create a record reader for a given split. The framework will call 92 * {@link RecordReader#initialize(InputSplit, TaskAttemptContext)} before 93 * the split is used. 94 * @param split the split to be read 95 * @param context the information about the task 96 * @return a new record reader 97 * @throws IOException 98 * @throws InterruptedException 99 */ 100 public abstract 101 RecordReader<K,V> createRecordReader(InputSplit split, 102 TaskAttemptContext context 103 ) throws IOException, 104 InterruptedException; 105 106 }
InputFormat源码
* <p>Each [email protected] InputSplit} is then assigned to an individual [email protected] Mapper} * for processing.</p>
*
* <p><i>Note</i>: The split is a <i>logical</i> split of the inputs and the
* input files are not physically split into chunks. For e.g. a split could
* be <i><input-file-path, start, offset></i> tuple. The InputFormat
* also creates the [email protected] RecordReader} to read the [email protected] InputSplit}.
*
* @param context job configuration.
* @return an array of [email protected] InputSplit}s for the job.
*/
public abstract
List<InputSplit> getSplits(JobContext context
) throws IOException, InterruptedException;
意思是：每一个文件逻辑上切分成若干个split(由getsplit方法)，一个split对应一个mapper任务
/** * Create a record reader for a given split. The framework will call * [email protected] RecordReader#initialize(InputSplit, TaskAttemptContext)} before * the split is used. * @param split the split to be read * @param context the information about the task * @return a new record reader * @throws IOException * @throws InterruptedException */ public abstract RecordReader<K,V> createRecordReader(InputSplit split, TaskAttemptContext context ) throws IOException, InterruptedException; }
意思是：split本质上是文件内容一部分，由RecordReader来处理文件内容(键值对)，进入RecordReader查看，可得该抽象类将data数据拆分成键值对，目的是输入给Mapper
/**
* The record reader breaks the data into key/value pairs for input to the
* [email protected] Mapper}.
* @param <KEYIN>
* @param <VALUEIN>
*/
public abstract class RecordReader<KEYIN, VALUEIN> implements Closeable {
/**
* Called once at initialization.
* @param split the split that defines the range of records to read
* @param context the information about the task
* @throws IOException
* @throws InterruptedException
*/
由此总结，源码分析的
文件———–通过———–>getsplits()———–分解为————>InputSplit————通过————–>RecordReader类(由createRecordReader()方法创建的)-——处理———->map(k1,v1)
第一部分：文件切分
问题1:如何将文件切分成split，查看自雷的getsplits()方法
1 /** 2 * Generate the list of files and make them into FileSplits. 3 * @param job the job context 4 * @throws IOException 5 */ 6 public List<InputSplit> getSplits(JobContext job) throws IOException { 7 Stopwatch sw = new Stopwatch().start(); 8 long minSize = Math.max(getFormatMinSplitSize(), getMinSplitSize(job)); 9 long maxSize = getMaxSplitSize(job); 10 11 // generate splits 12 List<InputSplit> splits = new ArrayList<InputSplit>(); 13 List<FileStatus> files = listStatus(job); 14 for (FileStatus file: files) { 15 Path path = file.getPath(); 16 long length = file.getLen(); 17 if (length != 0) { 18 BlockLocation[] blkLocations; 19 if (file instanceof LocatedFileStatus) { 20 blkLocations = ((LocatedFileStatus) file).getBlockLocations(); 21 } else { 22 FileSystem fs = path.getFileSystem(job.getConfiguration()); 23 blkLocations = fs.getFileBlockLocations(file, 0, length); 24 } 25 if (isSplitable(job, path)) { 26 long blockSize = file.getBlockSize(); 27 long splitSize = computeSplitSize(blockSize, minSize, maxSize); 28 29 long bytesRemaining = length; 30 while (((double) bytesRemaining)/splitSize > SPLIT_SLOP) { 31 int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining); 32 splits.add(makeSplit(path, length-bytesRemaining, splitSize, 33 blkLocations[blkIndex].getHosts(), 34 blkLocations[blkIndex].getCachedHosts())); 35 bytesRemaining -= splitSize; 36 } 37 38 if (bytesRemaining != 0) { 39 int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining); 40 splits.add(makeSplit(path, length-bytesRemaining, bytesRemaining, 41 blkLocations[blkIndex].getHosts(), 42 blkLocations[blkIndex].getCachedHosts())); 43 } 44 } else { // not splitable 45 splits.add(makeSplit(path, 0, length, blkLocations[0].getHosts(), 46 blkLocations[0].getCachedHosts())); 47 } 48 } else { 49 //Create empty hosts array for zero length files 50 splits.add(makeSplit(path, 0, length, new String[0])); 51 } 52 } 53 // Save the number of input files for metrics/loadgen 54 job.getConfiguration().setLong(NUM_INPUT_FILES, files.size()); 55 sw.stop(); 56 if (LOG.isDebugEnabled()) { 57 LOG.debug("Total # of splits generated by getSplits: " + splits.size() 58 + ", TimeTaken: " + sw.elapsedMillis()); 59 } 60 return splits; 61 }
getSplits
/** * Generate the list of files and make them into FileSplits. 将文件切分成split * @param job the job context * @throws IOException */
(1) 通过add方法将切片加入列表
(2)add方法中通过makesplit方法实现逻辑块的切分
（3）makeSplit内部使用FileSplit进行文件切分
(4)FileSplit三个参数的意义如下
hosts值得是包含块的节点列表，即block块。从start开始处理，处理多长length，处理的数据信息位于那个block块上，因此Split是逻辑切分
没有真正切分，如此对程序的影响，不会真正去读磁盘数据，而是使用HDFS读数据方法。
（5）分析文件长度不为0程序如何执行
if (length != 0) { BlockLocation[] blkLocations; if (file instanceof LocatedFileStatus) { blkLocations = ((LocatedFileStatus) file).getBlockLocations(); } else { FileSystem fs = path.getFileSystem(job.getConfiguration()); blkLocations = fs.getFileBlockLocations(file, 0, length); } if (isSplitable(job, path)) { //如果文件被切分，并非所有文件 都可以切分，比如密码文件，通常有文件结构决定是否可以被切分 long blockSize = file.getBlockSize(); long splitSize = computeSplitSize(blockSize, minSize, maxSize); long bytesRemaining = length; while (((double) bytesRemaining)/splitSize > SPLIT_SLOP) { int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining); splits.add(makeSplit(path, length-bytesRemaining, splitSize, //length-bytesRemaining为剩余字节
blkLocations[blkIndex].getHosts(),
blkLocations[blkIndex].getCachedHosts()));
bytesRemaining -= splitSize; }
- 如果文件大小300，length=300，bytesRemaining=300
- 执行第一次makesplit(0,128) 按splitSize=128切分
- bytesRemaining=300-128=172
- 执行第二次makesplit(300-172=128,128)
- bytesRemaining=172-128=44
- 执行第三次makesplit(300-44=256,128)
文件不允许被分割，执行以下程序
} else { // not splitable
splits.add(makeSplit(path, 0, length, blkLocations[0].getHosts(),
blkLocations[0].getCachedHosts()));
}
（6）分析文件块大小
380 long minSize = Math.max(getFormatMinSplitSize(), getMinSplitSize(job)); //结果分析为1L
381 long maxSize = getMaxSplitSize(job);//最大为Long的最大值
查看變量minsize的源代碼
long minSize = Math.max(getFormatMinSplitSize(), getMinSplitSize(job));
点击getFormatMinSplitSize()查看，为1L
/**
* Get the lower bound on split size imposed by the format.
* @return the number of bytes of the minimal split for this format
*/
protected long getFormatMinSplitSize() {
return 1;
}
点击getMinSplitSize()查看，计算办法为返回当前文件块的最小尺寸，如果配置文件中没有SPLIT_MINSIZE参数则返回1L
/**
* Get the minimum split size
* @param job the job
* @return the minimum number of bytes that can be in a split
*/
public static long getMinSplitSize(JobContext job) {
return job.getConfiguration().getLong(SPLIT_MINSIZE, 1L);
}
从而得到minsplit最小值为1L
而真正计算block是在399行，默认情况下inputsplit和block的大小均为128M，换句话说，一个map处理数据块的大小是一个block块大小
397 if (isSplitable(job, path)) { 398 long blockSize = file.getBlockSize(); 399 long splitSize = computeSplitSize(blockSize, minSize, maxSize);
当inputsplit和block的大小不同的时候，就会产生网络传输，如果inputsplit比block大，则inputsplit所需的是一个block块是不够的的，必须在找一个block块。
如果inputsplit比block小，block块中得一部分数据是没有被处理的，可能被别的map处理，也就可鞥产生网络传输，也是一种数据本地化的。
因为源码中使用的是for循环，因此，没一个文件都会去切分split
（7）两个50M，一个200M的文件和一个空文件会产生几个split
空白文件也会产生split，两个50M产生两个split，一个200M产生2个split，共需要5个map任务
**********************************************************
第二部分 通过createRecordReader()处理map任务
（1）解读createRecordReader
/** An {@link InputFormat} for plain text files. Files are broken into lines. * Either linefeed or carriage-return are used to signal end of line. Keys are * the position in the file, and values are the line of text.. */ @InterfaceAudience.Public @InterfaceStability.Stable public class TextInputFormat extends FileInputFormat<LongWritable, Text> { @Override public RecordReader<LongWritable, Text> createRecordReader(InputSplit split, TaskAttemptContext context) { String delimiter = context.getConfiguration().get( "textinputformat.record.delimiter"); byte[] recordDelimiterBytes = null; if (null != delimiter) recordDelimiterBytes = delimiter.getBytes(Charsets.UTF_8);//delimiter为分隔符，编码格式为utf-8，在解析的时候如果不是这个格式将会出错
return new LineRecordReader(recordDelimiterBytes); }
LineRecordReader为RecordReader的子类
/** * Treats keys as offset in file and value as line. key为偏移量，value为每一行的值 */ @InterfaceAudience.LimitedPrivate({"MapReduce", "Pig"}) @InterfaceStability.Evolving public class LineRecordReader extends RecordReader<LongWritable, Text> { private static final Log LOG = LogFactory.getLog(LineRecordReader.class); public static final String MAX_LINE_LENGTH = "mapreduce.input.linerecordreader.line.maxlength"; private long start; private long pos; private long end;
RecordReader类
/** * Called once at initialization. * @param split the split that defines the range of records to read * @param context the information about the task * @throws IOException * @throws InterruptedException */ public abstract void initialize(InputSplit split, //初始化，执行一次 TaskAttemptContext context ) throws IOException, InterruptedException; /** * Read the next key, value pair. * @return true if a key/value pair was read * @throws IOException * @throws InterruptedException */ public abstract //读取下一个键值对 这个键值对是map端的k1和v1 boolean nextKeyValue() throws IOException, InterruptedException; /** * Get the current key //得到key值 * @return the current key or null if there is no current key * @throws IOException * @throws InterruptedException */ public abstract KEYIN getCurrentKey() throws IOException, InterruptedException; /** * Get the current value. * @return the object that was read * @throws IOException * @throws InterruptedException */ public abstract VALUEIN getCurrentValue() throws IOException, InterruptedException; /** * The current progress of the record reader through its data. * @return a number between 0.0 and 1.0 that is the fraction of the data read * @throws IOException * @throws InterruptedException */ public abstract float getProgress() throws IOException, InterruptedException; /** * Close the record reader. */ public abstract void close() throws IOException; }
上述没有key和value的值，这是需要注意的，下面却提供了key和value的get方法，因此key和value在类的字段中存放，
在方法体中对key和value赋值，然后再利用getCurrentkey和getCurrentValue获得key和value。
比如：while(rs.next()){rs.getLong()}
Enumeration里面有一个hasMoreElement()方法也是上述情况，hashtable方法，用element做迭代，最后归结到Enumeration
因此上述程序可理解为：
while(rr.nextKeyValue()){key=rr.getCurrentKey(),value=rr.getCurrentValue(),map(key,value,context)}
通过源代码可以验证上述猜想，key和value的类型已经固定，因此在mapreduce中可以省略<k1,v1>不写
其中SplitLineReader为行读取器。
（2）
**split.getStart()处理被处理数据的起始位置，和行没有关系
起始位置赋给了pos当前位置，现在查找netKeyVAalue()方法
LineRecordReader类中
public boolean nextKeyValue() throws IOException { if (key == null) { key = new LongWritable(); } key.set(pos); if (value == null) { value = new Text(); } int newSize = 0; // We always read one extra line, which lies outside the upper // split limit i.e. (end - 1) while (getFilePosition() <= end || in.needAdditionalRecordAfterSplit()) { if (pos == 0) { newSize = skipUtfByteOrderMark(); } else { newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos)); pos += newSize; } if ((newSize == 0) || (newSize < maxLineLength)) { break; } // line too long. try again LOG.info("Skipped line of size " + newSize + " at pos " + (pos - newSize)); } if (newSize == 0) { key = null; value = null; return false; } else { return true; } }
如：hello you
hello me
上述文件中，会被切分成一个split，在这里
第一次调用nextKeyValue()的时候start=0，value=hello you，end=19,pos=0，key=0，newsize=10
第二次调用nextKeyValue()的时候key=10，value=hello me,newsize=10
由readLine()方法从输入流中读取给定文本，返回值为被读取字节的数量
newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos));读取一行数据，将数据放入value中，返回值为被读取字节的长度，还包括新行(换行)
总结，key和value的值就是通过nextKeyValue()方法赋值的。
第三部分 当key，value被赋值之后，剩下的问题就是如何被map函数所调用？
*****************************************************************
从map类分析：
/** * 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.mapreduce; import java.io.IOException; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.io.RawComparator; import org.apache.hadoop.io.compress.CompressionCodec; import org.apache.hadoop.mapreduce.task.MapContextImpl; /** * Maps input key/value pairs to a set of intermediate key/value pairs. * * <p>Maps are the individual tasks which transform input records into a * intermediate records. The transformed intermediate records need not be of * the same type as the input records. A given input pair may map to zero or * many output pairs.</p> * * <p>The Hadoop Map-Reduce framework spawns one map task for each * {@link InputSplit} generated by the {@link InputFormat} for the job. * <code>Mapper</code> implementations can access the {@link Configuration} for * the job via the {@link JobContext#getConfiguration()}. * * <p>The framework first calls * {@link #setup(org.apache.hadoop.mapreduce.Mapper.Context)}, followed by * {@link #map(Object, Object, Context)} * for each key/value pair in the <code>InputSplit</code>. Finally * {@link #cleanup(Context)} is called.</p> * * <p>All intermediate values associated with a given output key are * subsequently grouped by the framework, and passed to a {@link Reducer} to * determine the final output. Users can control the sorting and grouping by * specifying two key {@link RawComparator} classes.</p> * * <p>The <code>Mapper</code> outputs are partitioned per * <code>Reducer</code>. Users can control which keys (and hence records) go to * which <code>Reducer</code> by implementing a custom {@link Partitioner}. * * <p>Users can optionally specify a <code>combiner</code>, via * {@link Job#setCombinerClass(Class)}, to perform local aggregation of the * intermediate outputs, which helps to cut down the amount of data transferred * from the <code>Mapper</code> to the <code>Reducer</code>. * * <p>Applications can specify if and how the intermediate * outputs are to be compressed and which {@link CompressionCodec}s are to be * used via the <code>Configuration</code>.</p> * * <p>If the job has zero * reduces then the output of the <code>Mapper</code> is directly written * to the {@link OutputFormat} without sorting by keys.</p> * * <p>Example:</p> * <p><blockquote>* public class TokenCounterMapper * extends Mapper<Object, Text, Text, IntWritable>{ * * private final static IntWritable one = new IntWritable(1); * private Text word = new Text(); * * public void map(Object key, Text value, Context context) throws IOException, InterruptedException { * StringTokenizer itr = new StringTokenizer(value.toString()); * while (itr.hasMoreTokens()) { * word.set(itr.nextToken()); * context.write(word, one); * } * } * } *</blockquote></p>
@link #run(Context)} method to exert
*
* <p>Applications may override the {
* greater control on map processing e.g. multi-threaded <code>Mapper</code>s
* etc.</p>
*
* @see InputFormat
* @see JobContext
* @see Partitioner
* @see Reducer
*/
@InterfaceAudience.Public
@InterfaceStability.Stable
public class Mapper<KEYIN, VALUEIN, KEYOUT, VALUEOUT> {/**
* The <code>Context</code> passed on to the {@link Mapper} implementations.
*/
public abstract class Context
implements MapContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT> {
}/**
* Called once at the beginning of the task.任务执行开始调用
*/
protected void setup(Context context
) throws IOException, InterruptedException {
// NOTHING
}/**input split的每一个键值对都调用一次
* Called once for each key/value pair in the input split. Most applications
* should override this, but the default is the identity function.
*/
@SuppressWarnings("unchecked")
protected void map(KEYIN key, VALUEIN value,
Context context) throws IOException, InterruptedException {
context.write((KEYOUT) key, (VALUEOUT) value);
}/**
* Called once at the end of the task.
*/
protected void cleanup(Context context
) throws IOException, InterruptedException {
// NOTHING
}/**
* Expert users can override this method for more complete control over the
* execution of the Mapper.
* @param context
* @throws IOException
*/
public void run(Context context) throws IOException, InterruptedException {
setup(context); 执行一次
try {
while (context.nextKeyValue()) {
map(context.getCurrentKey(), context.getCurrentValue(), context);//一个inputsplit调用一次map函数
}
} finally {
cleanup(context); 执行一次
}
}
}
nextKeyValue()方法查看，
找到nextkeyvalue的实现，ctrl+t也可进入
MapContextImpl类下面提供了该类的实现
其种reader由RecordReader类提供
另外通过Context源码查看
进入该类
研究mapcontext，mapcontext是在构造函数中赋值的
查看WrappedMapper類的nextkeyvalue()方法
通過查看其實現，可以查找其實鮮類
可觀察到以下reader的實現情況
reader最終是有RecordReader來聲明的。
總結：
调用MapContextImpl有参构造方法，然后将RecordReader赋值进去(57行),从而可以调用80行的nextkeyvalue()方法，然后MapContextImpl的父类Context调用nextkeyvalue()
总结：从源代码的角度分析map函数处理的<k1,v1>是如何从HDFS文件中获取的？答：
1.从TextInputFormat入手分析，找到父类FileInputFormat，找到父类InputFormat。
在InputFormat中找到2个方法，分别是getSplits(…)和createRecordReader(…)。
通过注释知道getSplits(…)作用是把输入文件集合中的所有内容解析成一个个的InputSplits，每一个InputSplit对应一个mapper task。
createRecordReader(…)作用是创建一个RecordReader的实现类。RecordReader作用是解析InputSplit产生一个个的<k,v>。
2.在FileInputFormat中找到getSplits(…)的实现。
通过实现，获知
(1)每个SplitSize的大小和默认的block大小一致，好处是满足数据本地性。
(2)每个输入文件都会产生一个InputSplit，即使是空白文件，也会产生InputSPlit；
如果一个文件非常大，那么会按照InputSplit大小，切分产生多个InputSplit。
3.在TextInputFormat中找到createRecordReader(…)的实现，在方法中找到了LineRecordReader。
接下来分析LineRecordReader类。
在RecordReader类中，通过查看多个方法，知晓key、value作为类的属性存在的，且知道了nextKeyValue()方法的用法。
在LineRecordReader类中，重点分析了nextKeyValue(…)方法。在这个方法中，重点分析了newSize = in.readLine(value, maxLineLength, maxBytesToConsume(pos));
在in.readLine(…)中，第一个形参存储被读取的行文本内容，返回值表示被读取内容的字节数。
通过以上代码，分析了InputSplit中的内容是如何转化为一个个的<k,v>。
4.从Mapper类中进行分析，发现了setup()、cleanup()、map()、run()。
在run()方法中，通过while，调用context.nextKeyValue(…)。
进一步分析Context的接口类是org.apache.hadoop.mapreduce.lib.map.WrappedMapper.MapContext，MapContext调用了nextKeyValue(…)。最终找到了MapContext的实现了MapContextImpl类org.apache.hadoop.mapreduce.task.MapContextImpl。
在这个类的构造方法中，发现传入了RecordReader的实现类。
原创文章，作者：奋斗，如若转载，请注明出处：https://blog.ytso.com/9094.html