Java tutorial
/*
* Cloud9: A Hadoop toolkit for working with big data
*
* Licensed 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.
*/
import java.io.IOException;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.CommandLineParser;
import org.apache.commons.cli.GnuParser;
import org.apache.commons.cli.HelpFormatter;
import org.apache.commons.cli.OptionBuilder;
import org.apache.commons.cli.Options;
import org.apache.commons.cli.ParseException;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.MapFileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import org.apache.log4j.Logger;
import tl.lin.data.array.ArrayListWritable;
import tl.lin.data.fd.Object2IntFrequencyDistribution;
import tl.lin.data.fd.Object2IntFrequencyDistributionEntry;
import tl.lin.data.pair.PairOfInts;
import tl.lin.data.pair.PairOfObjectInt;
import tl.lin.data.pair.PairOfWritables;
public class BuildInvertedIndex extends Configured implements Tool {
private static final Logger LOG = Logger.getLogger(BuildInvertedIndex.class);
private static class MyMapper extends Mapper<LongWritable, Text, Text, PairOfInts> {
private static final Text WORD = new Text();
// private static final Object2IntFrequencyDistribution<String> COUNTS =
// new Object2IntFrequencyDistributionEntry<String>();
private static final HashMap<String, Integer> COUNTS = new HashMap<String, Integer>();
@Override
public void map(LongWritable docno, Text doc, Context context) throws IOException, InterruptedException {
String text = doc.toString();
COUNTS.clear();
String[] terms = text.split("\\s+");
// First build a histogram of the terms.
for (String term : terms) {
if (term == null || term.length() == 0) {
continue;
}
if (COUNTS.containsKey(term)) {
COUNTS.put(/* fill in your code here */);
} else {
COUNTS.put(/* fill in your code here */);
}
}
// Emit postings.
for (Entry<String, Integer> entry : COUNTS.entrySet()) {
WORD.set(entry.getKey());
context.write(WORD, new PairOfInts((int) docno.get(), entry.getValue()));
}
}
}
private static class MyReducer
extends Reducer<Text, PairOfInts, Text, PairOfWritables<IntWritable, ArrayListWritable<PairOfInts>>> {
private final static IntWritable DF = new IntWritable();
@Override
public void reduce(Text key, Iterable<PairOfInts> values, Context context)
throws IOException, InterruptedException {
// Iterator<PairOfInts> iter = values.iterator();
ArrayListWritable<PairOfInts> postings = new ArrayListWritable<PairOfInts>();
int df = 0;
for (PairOfInts pair : values) {
/* fill in your code here */++;
/* fill in your code here */.add(pair.clone());
}
// Sort the postings by docno ascending.
Collections.sort(postings);
DF.set(df);
context.write(key,
new PairOfWritables<IntWritable, ArrayListWritable<PairOfInts>>(DF, postings));
}
}
private BuildInvertedIndex() {
}
private static final String INPUT = "input";
private static final String OUTPUT = "output";
private static final String NUM_REDUCERS = "numReducers";
/**
* Runs this tool.
*/
@SuppressWarnings({ "static-access" })
public int run(String[] args) throws Exception {
Options options = new Options();
options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("input path").create(INPUT));
options.addOption(OptionBuilder.withArgName("path").hasArg().withDescription("output path").create(OUTPUT));
options.addOption(OptionBuilder.withArgName("num").hasArg().withDescription("number of reducers")
.create(NUM_REDUCERS));
CommandLine cmdline;
CommandLineParser parser = new GnuParser();
try {
cmdline = parser.parse(options, args);
} catch (ParseException exp) {
System.err.println("Error parsing command line: " + exp.getMessage());
return -1;
}
if (!cmdline.hasOption(INPUT) || !cmdline.hasOption(OUTPUT)) {
System.out.println("args: " + Arrays.toString(args));
HelpFormatter formatter = new HelpFormatter();
formatter.setWidth(120);
formatter.printHelp(this.getClass().getName(), options);
ToolRunner.printGenericCommandUsage(System.out);
return -1;
}
String inputPath = cmdline.getOptionValue(INPUT);
String outputPath = cmdline.getOptionValue(OUTPUT);
int reduceTasks = cmdline.hasOption(NUM_REDUCERS) ? Integer.parseInt(cmdline.getOptionValue(NUM_REDUCERS))
: 1;
LOG.info("Tool name: " + BuildInvertedIndex.class.getSimpleName());
LOG.info(" - input path: " + inputPath);
LOG.info(" - output path: " + outputPath);
LOG.info(" - num reducers: " + reduceTasks);
Job job = Job.getInstance(getConf());
job.setJobName(BuildInvertedIndex.class.getSimpleName());
job.setJarByClass(BuildInvertedIndex.class);
job.setNumReduceTasks(reduceTasks);
FileInputFormat.setInputPaths(job, new Path(inputPath));
FileOutputFormat.setOutputPath(job, new Path(outputPath));
job.setMapOutputKeyClass(Text.class);
job.setMapOutputValueClass(PairOfInts.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(PairOfWritables.class);
job.setOutputFormatClass(TextOutputFormat.class);
job.setMapperClass(MyMapper.class);
job.setReducerClass(MyReducer.class);
// Delete the output directory if it exists already.
Path outputDir = new Path(outputPath);
FileSystem.get(getConf()).delete(outputDir, true);
long startTime = System.currentTimeMillis();
job.waitForCompletion(true);
System.out.println("Job Finished in " + (System.currentTimeMillis() - startTime) / 1000.0 + " seconds");
return 0;
}
/**
* Dispatches command-line arguments to the tool via the {@code ToolRunner}.
*/
public static void main(String[] args) throws Exception {
ToolRunner.run(new BuildInvertedIndex(), args);
}
}