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 com.linkedin.whiteelephant.mapreduce; import java.io.IOException; import java.util.Map; import java.util.StringTokenizer; import java.util.List; import java.util.Set; import java.util.HashMap; import java.util.ArrayList; import java.util.HashSet; import java.util.Collections; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.util.ReflectionUtils; import org.apache.hadoop.mapreduce.TaskAttemptContext; import org.apache.hadoop.mapreduce.RecordWriter; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.JobContext; import org.apache.hadoop.mapreduce.OutputFormat; import org.apache.hadoop.mapreduce.TaskInputOutputContext; import org.apache.hadoop.io.NullWritable; import org.apache.avro.Schema; import org.apache.avro.mapreduce.AvroJob; /** * The AvroMultipleOutputs class simplifies writing Avro 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>Schema</code> and <code>OutputFormat</code>. * </p> * <p> * Case two: to write data to different files provided by user * </p> * * <p> * AvroMultipleOutputs supports counters, by default they are disabled. The * counters group is the {@link AvroMultipleOutputs} class name. The names of the * counters are the same as the output name. These count the number of 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(MyAvroMapper.class); * job.setReducerClass(MyAvroReducer.class); * ... * * Schema schema; * ... * // Defines additional single output 'avro1' for the job * AvroMultipleOutputs.addNamedOutput(job, "avro1", AvroKeyValueOutputFormat.class, * keyschema, valueSchema); // valueSchema can be set to null if there only Key to be written to file in the RecordWriter * * // Defines additional output 'avro2' with different schema for the job * AvroMultipleOutputs.addNamedOutput(job, "avro2", * AvroKeyOutputFormat.class, * schema,null); * ... * * job.waitForCompletion(true); * ... * </pre> * <p> * Usage in Reducer: * <pre> * * public class MyAvroReducer extends * Reducer<K, V, T, NullWritable> { * private MultipleOutputs amos; * * * public void setup(Context context) { * ... * amos = new AvroMultipleOutputs(context); * } * * public void reduce(K, Iterator<V> values,Context context) * throws IOException { * ... * amos.write("avro1",datum,NullWritable.get()); * amos.write("avro2",datum,NullWritable.get()); * amos.getCollector("avro3",datum); // here the value is taken as NullWritable * ... * } * * public void cleanup(Context context) throws IOException { * amos.close(); * ... * } * * } * </pre> */ // patched version of AvroMultipleOutputs which actually works public class MyAvroMultipleOutputs { private static final String MULTIPLE_OUTPUTS = "avro.mapreduce.multipleoutputs"; private static final String MO_PREFIX = "avro.mapreduce.multipleoutputs.namedOutput."; private static final String FORMAT = ".format"; private static final String COUNTERS_ENABLED = "avro.mapreduce.multipleoutputs.counters"; /** * Counters group used by the counters of MultipleOutputs. */ private static final String COUNTERS_GROUP = MyAvroMultipleOutputs.class.getName(); /** * Cache for the taskContexts */ private Map<String, TaskAttemptContext> taskContexts = new HashMap<String, TaskAttemptContext>(); /** * Cache for the Key Schemas */ private static Map<String, Schema> keySchemas = new HashMap<String, Schema>(); /** * Cache for the Value Schemas */ private static Map<String, Schema> valSchemas = new HashMap<String, Schema>(); /** * 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("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); } /** * Adds a named output for the job. * <p/> * * @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 keySchema Schema for the Key */ @SuppressWarnings("unchecked") public static void addNamedOutput(Job job, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema keySchema) { addNamedOutput(job, namedOutput, outputFormatClass, keySchema, null); } /** * Adds a named output for the job. * <p/> * * @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 keySchema Schema for the Key * @param valueSchema Schema for the Value (used in case of AvroKeyValueOutputFormat or null) */ @SuppressWarnings("unchecked") public static void addNamedOutput(Job job, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema keySchema, Schema valueSchema) { 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); keySchemas.put(namedOutput + "_KEYSCHEMA", keySchema); valSchemas.put(namedOutput + "_VALSCHEMA", valueSchema); } /** * 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<?, ?, ?, ?> 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 MyAvroMultipleOutputs(TaskInputOutputContext<?, ?, ?, ?> context) { this.context = context; namedOutputs = Collections .unmodifiableSet(new HashSet<String>(MyAvroMultipleOutputs.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 , value is NullWritable */ @SuppressWarnings("unchecked") public void write(String namedOutput, Object key) throws IOException, InterruptedException { write(namedOutput, key, NullWritable.get(), namedOutput); } /** * 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 void write(String namedOutput, Object key, Object 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 */ @SuppressWarnings("unchecked") public void write(String namedOutput, Object key, Object 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 */ @SuppressWarnings("unchecked") public void write(Object key, Object value, String baseOutputPath) throws IOException, InterruptedException { checkBaseOutputPath(baseOutputPath); TaskAttemptContext taskContext = new TaskAttemptContext(context.getConfiguration(), context.getTaskAttemptID()); getRecordWriter(taskContext, 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); // (mhayes) Fix so can write to different baseFileName // * Bug reported here: https://issues.apache.org/jira/browse/AVRO-1215 // * Original code submitted here: https://issues.apache.org/jira/browse/AVRO-1106 taskContext.getConfiguration().set("avro.mo.config.namedOutput", 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. context.getConfiguration().set("avro.mo.config.namedOutput", nameOutput); Job job = new Job(context.getConfiguration()); job.setOutputFormatClass(getNamedOutputFormatClass(context, nameOutput)); Schema keySchema = keySchemas.get(nameOutput + "_KEYSCHEMA"); Schema valSchema = valSchemas.get(nameOutput + "_VALSCHEMA"); boolean isMaponly = job.getNumReduceTasks() == 0; if (keySchema != null) { if (isMaponly) AvroJob.setMapOutputKeySchema(job, keySchema); else AvroJob.setOutputKeySchema(job, keySchema); } if (valSchema != null) { if (isMaponly) AvroJob.setMapOutputValueSchema(job, valSchema); else AvroJob.setOutputValueSchema(job, valSchema); } taskContext = new TaskAttemptContext(job.getConfiguration(), context.getTaskAttemptID()); taskContexts.put(nameOutput, taskContext); return taskContext; } /** * 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); } } }