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.mapreduce.lib.output; import org.apache.hadoop.classification.InterfaceAudience; import org.apache.hadoop.classification.InterfaceStability; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.*; import org.apache.hadoop.mapreduce.Reducer.Context; import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs; import org.apache.hadoop.mapreduce.task.TaskAttemptContextImpl; import org.apache.hadoop.util.ReflectionUtils; import java.io.IOException; import java.util.*; /** * The MultipleOutputs class simplifies writing output data * to multiple outputs * * <p> * Case one: writing to additional outputs other than the job default output. * * Each additional output, or named output, may be configured with its own * <code>OutputFormat</code>, with its own key class and with its own value * class. * </p> * * <p> * Case two: to write data to different files provided by user * </p> * * <p> * MultipleOutputs supports counters, by default they are disabled. The * counters group is the {@link MultipleOutputs} class name. The names of the * counters are the same as the output name. These count the number records * written to each output name. * </p> * * Usage pattern for job submission: * <pre> * * Job job = new Job(); * * FileInputFormat.setInputPath(job, inDir); * FileOutputFormat.setOutputPath(job, outDir); * * job.setMapperClass(MOMap.class); * job.setReducerClass(MOReduce.class); * ... * * // Defines additional single text based output 'text' for the job * MultipleOutputs.addNamedOutput(job, "text", TextOutputFormat.class, * LongWritable.class, Text.class); * * // Defines additional sequence-file based output 'sequence' for the job * MultipleOutputs.addNamedOutput(job, "seq", * SequenceFileOutputFormat.class, * LongWritable.class, Text.class); * ... * * job.waitForCompletion(true); * ... * </pre> * <p> * Usage in Reducer: * <pre> * <K, V> String generateFileName(K k, V v) { * return k.toString() + "_" + v.toString(); * } * * public class MOReduce extends * Reducer<WritableComparable, Writable,WritableComparable, Writable> { * private MultipleOutputs mos; * public void setup(Context context) { * ... * mos = new MultipleOutputs(context); * } * * public void reduce(WritableComparable key, Iterator<Writable> values, * Context context) * throws IOException { * ... * mos.write("text", , key, new Text("Hello")); * mos.write("seq", LongWritable(1), new Text("Bye"), "seq_a"); * mos.write("seq", LongWritable(2), key, new Text("Chau"), "seq_b"); * mos.write(key, new Text("value"), generateFileName(key, new Text("value"))); * ... * } * * public void cleanup(Context) throws IOException { * mos.close(); * ... * } * * } * </pre> * * <p> * When used in conjuction with org.apache.hadoop.mapreduce.lib.output.LazyOutputFormat, * MultipleOutputs can mimic the behaviour of MultipleTextOutputFormat and MultipleSequenceFileOutputFormat * from the old Hadoop API - ie, output can be written from the Reducer to more than one location. * </p> * * <p> * Use <code>MultipleOutputs.write(KEYOUT key, VALUEOUT value, String baseOutputPath)</code> to write key and * value to a path specified by <code>baseOutputPath</code>, with no need to specify a named output. * <b>Warning</b>: when the baseOutputPath passed to MultipleOutputs.write * is a path that resolves outside of the final job output directory, the * directory is created immediately and then persists through subsequent * task retries, breaking the concept of output committing: * </p> * * <pre> * private MultipleOutputs<Text, Text> out; * * public void setup(Context context) { * out = new MultipleOutputs<Text, Text>(context); * ... * } * * public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException { * for (Text t : values) { * out.write(key, t, generateFileName(<<i>parameter list...</i>>)); * } * } * * protected void cleanup(Context context) throws IOException, InterruptedException { * out.close(); * } * </pre> * * <p> * Use your own code in <code>generateFileName()</code> to create a custom path to your results. * '/' characters in <code>baseOutputPath</code> will be translated into directory levels in your file system. * Also, append your custom-generated path with "part" or similar, otherwise your output will be -00000, -00001 etc. * No call to <code>context.write()</code> is necessary. See example <code>generateFileName()</code> code below. * </p> * * <pre> * private String generateFileName(Text k) { * // expect Text k in format "Surname|Forename" * String[] kStr = k.toString().split("\\|"); * * String sName = kStr[0]; * String fName = kStr[1]; * * // example for k = Smith|John * // output written to /user/hadoop/path/to/output/Smith/John-r-00000 (etc) * return sName + "/" + fName; * } * </pre> * * <p> * Using MultipleOutputs in this way will still create zero-sized default output, eg part-00000. * To prevent this use <code>LazyOutputFormat.setOutputFormatClass(job, TextOutputFormat.class);</code> * instead of <code>job.setOutputFormatClass(TextOutputFormat.class);</code> in your Hadoop job configuration. * </p> * */ @InterfaceAudience.Public @InterfaceStability.Stable public class MultipleOutputs<KEYOUT, VALUEOUT> { private static final String MULTIPLE_OUTPUTS = "mapreduce.multipleoutputs"; private static final String MO_PREFIX = "mapreduce.multipleoutputs.namedOutput."; private static final String FORMAT = ".format"; private static final String KEY = ".key"; private static final String VALUE = ".value"; private static final String COUNTERS_ENABLED = "mapreduce.multipleoutputs.counters"; /** * Counters group used by the counters of MultipleOutputs. */ private static final String COUNTERS_GROUP = MultipleOutputs.class.getName(); /** * Cache for the taskContexts */ private Map<String, TaskAttemptContext> taskContexts = new HashMap<String, TaskAttemptContext>(); /** * Cached TaskAttemptContext which uses the job's configured settings */ private TaskAttemptContext jobOutputFormatContext; /** * Checks if a named output name is valid token. * * @param namedOutput named output Name * @throws IllegalArgumentException if the output name is not valid. */ private static void checkTokenName(String namedOutput) { if (namedOutput == null || namedOutput.length() == 0) { throw new IllegalArgumentException("Name cannot be NULL or emtpy"); } for (char ch : namedOutput.toCharArray()) { if ((ch >= 'A') && (ch <= 'Z')) { continue; } if ((ch >= 'a') && (ch <= 'z')) { continue; } if ((ch >= '0') && (ch <= '9')) { continue; } throw new IllegalArgumentException("Name cannot be have a '" + ch + "' char"); } } /** * Checks if output name is valid. * * name cannot be the name used for the default output * @param outputPath base output Name * @throws IllegalArgumentException if the output name is not valid. */ private static void checkBaseOutputPath(String outputPath) { if (outputPath.equals(FileOutputFormat.PART)) { throw new IllegalArgumentException("output name cannot be 'part'"); } } /** * Checks if a named output name is valid. * * @param namedOutput named output Name * @throws IllegalArgumentException if the output name is not valid. */ private static void checkNamedOutputName(JobContext job, String namedOutput, boolean alreadyDefined) { checkTokenName(namedOutput); checkBaseOutputPath(namedOutput); List<String> definedChannels = getNamedOutputsList(job); if (alreadyDefined && definedChannels.contains(namedOutput)) { throw new IllegalArgumentException("Named output '" + namedOutput + "' already alreadyDefined"); } else if (!alreadyDefined && !definedChannels.contains(namedOutput)) { throw new IllegalArgumentException("Named output '" + namedOutput + "' not defined"); } } // Returns list of channel names. private static List<String> getNamedOutputsList(JobContext job) { List<String> names = new ArrayList<String>(); StringTokenizer st = new StringTokenizer(job.getConfiguration().get(MULTIPLE_OUTPUTS, ""), " "); while (st.hasMoreTokens()) { names.add(st.nextToken()); } return names; } // Returns the named output OutputFormat. @SuppressWarnings("unchecked") private static Class<? extends OutputFormat<?, ?>> getNamedOutputFormatClass(JobContext job, String namedOutput) { return (Class<? extends OutputFormat<?, ?>>) job.getConfiguration() .getClass(MO_PREFIX + namedOutput + FORMAT, null, OutputFormat.class); } // Returns the key class for a named output. private static Class<?> getNamedOutputKeyClass(JobContext job, String namedOutput) { return job.getConfiguration().getClass(MO_PREFIX + namedOutput + KEY, null, Object.class); } // Returns the value class for a named output. private static Class<?> getNamedOutputValueClass(JobContext job, String namedOutput) { return job.getConfiguration().getClass(MO_PREFIX + namedOutput + VALUE, null, Object.class); } /** * Adds a named output for the job. * * @param job job to add the named output * @param namedOutput named output name, it has to be a word, letters * and numbers only, cannot be the word 'part' as * that is reserved for the default output. * @param outputFormatClass OutputFormat class. * @param keyClass key class * @param valueClass value class */ @SuppressWarnings("unchecked") public static void addNamedOutput(Job job, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Class<?> keyClass, Class<?> valueClass) { checkNamedOutputName(job, namedOutput, true); Configuration conf = job.getConfiguration(); conf.set(MULTIPLE_OUTPUTS, conf.get(MULTIPLE_OUTPUTS, "") + " " + namedOutput); conf.setClass(MO_PREFIX + namedOutput + FORMAT, outputFormatClass, OutputFormat.class); conf.setClass(MO_PREFIX + namedOutput + KEY, keyClass, Object.class); conf.setClass(MO_PREFIX + namedOutput + VALUE, valueClass, Object.class); } /** * Enables or disables counters for the named outputs. * * The counters group is the {@link MultipleOutputs} class name. * The names of the counters are the same as the named outputs. These * counters count the number records written to each output name. * By default these counters are disabled. * * @param job job to enable counters * @param enabled indicates if the counters will be enabled or not. */ public static void setCountersEnabled(Job job, boolean enabled) { job.getConfiguration().setBoolean(COUNTERS_ENABLED, enabled); } /** * Returns if the counters for the named outputs are enabled or not. * By default these counters are disabled. * * @param job the job * @return TRUE if the counters are enabled, FALSE if they are disabled. */ public static boolean getCountersEnabled(JobContext job) { return job.getConfiguration().getBoolean(COUNTERS_ENABLED, false); } /** * Wraps RecordWriter to increment counters. */ @SuppressWarnings("unchecked") private static class RecordWriterWithCounter extends RecordWriter { private RecordWriter writer; private String counterName; private TaskInputOutputContext context; public RecordWriterWithCounter(RecordWriter writer, String counterName, TaskInputOutputContext context) { this.writer = writer; this.counterName = counterName; this.context = context; } @SuppressWarnings({ "unchecked" }) public void write(Object key, Object value) throws IOException, InterruptedException { context.getCounter(COUNTERS_GROUP, counterName).increment(1); writer.write(key, value); } public void close(TaskAttemptContext context) throws IOException, InterruptedException { writer.close(context); } } // instance code, to be used from Mapper/Reducer code private TaskInputOutputContext<?, ?, KEYOUT, VALUEOUT> context; private Set<String> namedOutputs; private Map<String, RecordWriter<?, ?>> recordWriters; private boolean countersEnabled; /** * Creates and initializes multiple outputs support, * it should be instantiated in the Mapper/Reducer setup method. * * @param context the TaskInputOutputContext object */ public MultipleOutputs(TaskInputOutputContext<?, ?, KEYOUT, VALUEOUT> context) { this.context = context; namedOutputs = Collections .unmodifiableSet(new HashSet<String>(MultipleOutputs.getNamedOutputsList(context))); recordWriters = new HashMap<String, RecordWriter<?, ?>>(); countersEnabled = getCountersEnabled(context); } /** * Write key and value to the namedOutput. * * Output path is a unique file generated for the namedOutput. * For example, {namedOutput}-(m|r)-{part-number} * * @param namedOutput the named output name * @param key the key * @param value the value */ @SuppressWarnings("unchecked") public <K, V> void write(String namedOutput, K key, V value) throws IOException, InterruptedException { write(namedOutput, key, value, namedOutput); } /** * Write key and value to baseOutputPath using the namedOutput. * * @param namedOutput the named output name * @param key the key * @param value the value * @param baseOutputPath base-output path to write the record to. * Note: Framework will generate unique filename for the baseOutputPath * <b>Warning</b>: when the baseOutputPath is a path that resolves * outside of the final job output directory, the directory is created * immediately and then persists through subsequent task retries, breaking * the concept of output committing. */ @SuppressWarnings("unchecked") public <K, V> void write(String namedOutput, K key, V value, String baseOutputPath) throws IOException, InterruptedException { checkNamedOutputName(context, namedOutput, false); checkBaseOutputPath(baseOutputPath); if (!namedOutputs.contains(namedOutput)) { throw new IllegalArgumentException("Undefined named output '" + namedOutput + "'"); } TaskAttemptContext taskContext = getContext(namedOutput); getRecordWriter(taskContext, baseOutputPath).write(key, value); } /** * Write key value to an output file name. * * Gets the record writer from job's output format. * Job's output format should be a FileOutputFormat. * * @param key the key * @param value the value * @param baseOutputPath base-output path to write the record to. * Note: Framework will generate unique filename for the baseOutputPath * <b>Warning</b>: when the baseOutputPath is a path that resolves * outside of the final job output directory, the directory is created * immediately and then persists through subsequent task retries, breaking * the concept of output committing. */ @SuppressWarnings("unchecked") public void write(KEYOUT key, VALUEOUT value, String baseOutputPath) throws IOException, InterruptedException { checkBaseOutputPath(baseOutputPath); if (jobOutputFormatContext == null) { jobOutputFormatContext = new TaskAttemptContextImpl(context.getConfiguration(), context.getTaskAttemptID(), new WrappedStatusReporter(context)); } getRecordWriter(jobOutputFormatContext, baseOutputPath).write(key, value); } // by being synchronized MultipleOutputTask can be use with a // MultithreadedMapper. @SuppressWarnings("unchecked") private synchronized RecordWriter getRecordWriter(TaskAttemptContext taskContext, String baseFileName) throws IOException, InterruptedException { // look for record-writer in the cache RecordWriter writer = recordWriters.get(baseFileName); // If not in cache, create a new one if (writer == null) { // get the record writer from context output format FileOutputFormat.setOutputName(taskContext, baseFileName); try { writer = ((OutputFormat) ReflectionUtils.newInstance(taskContext.getOutputFormatClass(), taskContext.getConfiguration())).getRecordWriter(taskContext); } catch (ClassNotFoundException e) { throw new IOException(e); } // if counters are enabled, wrap the writer with context // to increment counters if (countersEnabled) { writer = new RecordWriterWithCounter(writer, baseFileName, context); } // add the record-writer to the cache recordWriters.put(baseFileName, writer); } return writer; } // Create a taskAttemptContext for the named output with // output format and output key/value types put in the context private TaskAttemptContext getContext(String nameOutput) throws IOException { TaskAttemptContext taskContext = taskContexts.get(nameOutput); if (taskContext != null) { return taskContext; } // The following trick leverages the instantiation of a record writer via // the job thus supporting arbitrary output formats. Job job = Job.getInstance(context.getConfiguration()); job.setOutputFormatClass(getNamedOutputFormatClass(context, nameOutput)); job.setOutputKeyClass(getNamedOutputKeyClass(context, nameOutput)); job.setOutputValueClass(getNamedOutputValueClass(context, nameOutput)); taskContext = new TaskAttemptContextImpl(job.getConfiguration(), context.getTaskAttemptID(), new WrappedStatusReporter(context)); taskContexts.put(nameOutput, taskContext); return taskContext; } private static class WrappedStatusReporter extends StatusReporter { TaskAttemptContext context; public WrappedStatusReporter(TaskAttemptContext context) { this.context = context; } @Override public Counter getCounter(Enum<?> name) { return context.getCounter(name); } @Override public Counter getCounter(String group, String name) { return context.getCounter(group, name); } @Override public void progress() { context.progress(); } @Override public float getProgress() { return context.getProgress(); } @Override public void setStatus(String status) { context.setStatus(status); } } /** * Closes all the opened outputs. * * This should be called from cleanup method of map/reduce task. * If overridden subclasses must invoke <code>super.close()</code> at the * end of their <code>close()</code> * */ @SuppressWarnings("unchecked") public void close() throws IOException, InterruptedException { for (RecordWriter writer : recordWriters.values()) { writer.close(context); } } }