使用Hortonworks Sanbox 练习 Hadoop 和 MapReduce

最近在上Coursera的云计算系列课程。在Cloud Application里面，需要提交练习编写MapReduce的作业。便捷模拟Hadoop环境的虚拟机是Hortonworks Sanbox。

开机之后可以SSH登陆，127.0.0.1:2222

# 添加环境变量
export HADOOP_CLASSPATH=$JAVA_HOME/lib/tools.jar
# 编译
hadoop com.sun.tools.javac.Main  TopTitleStatistics.java  -d build
# 打包jar
jar -cvf  TopTitleStatistics.jar -C build/ ./
# 执行
hadoop jar TopTitleStatistics.jar TopTitleStatistics -D stopwords=/mp2/misc/stopwords.txt -D delimiters=/mp2/misc/delimiters.txt -D N=5 /mp2/titles /mp2/C-output

# 查看输出结果
hadoop fs -cat /mp2/C-output/part* | head -n 100

# 删除输出和编译结果（如果要重新运行，必须删除输出）
hadoop fs -rm -r /mp2/C-output
rm -rf ./build/* ./TopTitleStatistics.jar

附源码

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.ArrayWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
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.input.KeyValueTextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.List;
import java.util.StringTokenizer;
import java.util.TreeSet;

/* * TopTitles.java */

// >>> Don't Change
public class TopTitles extends Configured implements Tool {

    public static void main(String[] args) throws Exception {
        int res = ToolRunner.run(new Configuration(), new TopTitles(), args);
        System.exit(res);
    }

    @Override
    public int run(String[] args) throws Exception {
        Configuration conf = this.getConf();
        FileSystem fs = FileSystem.get(conf);
        Path tmpPath = new Path("/mp2/tmp");
        fs.delete(tmpPath, true);

        Job jobA = Job.getInstance(conf, "Title Count");
        jobA.setOutputKeyClass(Text.class);
        jobA.setOutputValueClass(IntWritable.class);

        jobA.setMapperClass(TitleCountMap.class);
        jobA.setReducerClass(TitleCountReduce.class);

        FileInputFormat.setInputPaths(jobA, new Path(args[0]));
        FileOutputFormat.setOutputPath(jobA, tmpPath);

        jobA.setJarByClass(TopTitles.class);
        jobA.waitForCompletion(true);

        Job jobB = Job.getInstance(conf, "Top Titles");
        jobB.setOutputKeyClass(Text.class);
        jobB.setOutputValueClass(IntWritable.class);

        jobB.setMapOutputKeyClass(NullWritable.class);
        jobB.setMapOutputValueClass(TextArrayWritable.class);

        jobB.setMapperClass(TopTitlesMap.class);
        jobB.setReducerClass(TopTitlesReduce.class);
        jobB.setNumReduceTasks(1);

        FileInputFormat.setInputPaths(jobB, tmpPath);
        FileOutputFormat.setOutputPath(jobB, new Path(args[1]));

        jobB.setInputFormatClass(KeyValueTextInputFormat.class);
        jobB.setOutputFormatClass(TextOutputFormat.class);

        jobB.setJarByClass(TopTitles.class);
        return jobB.waitForCompletion(true) ? 0 : 1;
    }

    public static String readHDFSFile(String path, Configuration conf) throws IOException{
        Path pt=new Path(path);
        FileSystem fs = FileSystem.get(pt.toUri(), conf);
        FSDataInputStream file = fs.open(pt);
        BufferedReader buffIn=new BufferedReader(new InputStreamReader(file));

        StringBuilder everything = new StringBuilder();
        String line;
        while( (line = buffIn.readLine()) != null) {
            everything.append(line);
            everything.append("\n");
        }
        return everything.toString();
    }

    public static class TextArrayWritable extends ArrayWritable {
        public TextArrayWritable() {
            super(Text.class);
        }

        public TextArrayWritable(String[] strings) {
            super(Text.class);
            Text[] texts = new Text[strings.length];
            for (int i = 0; i < strings.length; i++) {
                texts[i] = new Text(strings[i]);
            }
            set(texts);
        }
    }
// <<< Don't Change

    public static class TitleCountMap extends Mapper<Object, Text, Text, IntWritable> {
        List<String> stopWords;
        String delimiters;

        @Override
        protected void setup(Context context) throws IOException,InterruptedException {

            Configuration conf = context.getConfiguration();

            String stopWordsPath = conf.get("stopwords");
            String delimitersPath = conf.get("delimiters");

            this.stopWords = Arrays.asList(readHDFSFile(stopWordsPath, conf).split("\n"));
            this.delimiters = readHDFSFile(delimitersPath, conf);
        }


        @Override
        public void map(Object key, Text value, Context context) throws IOException, InterruptedException {
        // TODO
            String line = value.toString();
            StringTokenizer st = new StringTokenizer(line, delimiters);
            while (st.hasMoreTokens()) {
                String word = (st.nextToken()).trim().toLowerCase();
                if (!stopWords.contains(word)) {
                    context.write(new Text(word), new IntWritable(1));
                }
            }
        }
    }

    public static class TitleCountReduce extends Reducer<Text, IntWritable, Text, IntWritable> {
        @Override
        public void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            // TODO
            int sum = 0;
            for (IntWritable val: values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }

    public static class TopTitlesMap extends Mapper<Text, Text, NullWritable, TextArrayWritable> {
        Integer N;
        // TODO
        /* * add TreeSet. Item in treeset are sorted acsended * sorted by KEY automatically */
        TreeSet<Pair<Integer,String>> titleCountMap = new TreeSet<Pair<Integer,String>>();

        @Override
        protected void setup(Context context) throws IOException,InterruptedException {
            Configuration conf = context.getConfiguration();
            this.N = conf.getInt("N", 10);
        }

        @Override
        public void map(Text key, Text value, Context context) throws IOException, InterruptedException {
            // TODO
            String word = key.toString();
            Integer count = Integer.parseInt(value.toString());

            titleCountMap.add(new Pair<Integer,String>(count,word));
            if (titleCountMap.size() > N) {  //remove too much items, no more than N (default 10)
                titleCountMap.remove(titleCountMap.first());
            }
        }

        @Override
        protected void cleanup(Context context) throws IOException, InterruptedException {
            // TODO
            //When mapper is nearly finish, method cleanup() is called
            for (Pair<Integer,String> item: titleCountMap) {
                String[] strings = {item.second, item.first.toString()};

                TextArrayWritable val = new TextArrayWritable(strings);
                context.write(NullWritable.get(), val);
            }
        }
    }

    public static class TopTitlesReduce extends Reducer<NullWritable, TextArrayWritable, Text, IntWritable> {
        Integer N;
        // TODO
        TreeSet<Pair<Integer,String>> titleCountMap = new TreeSet<Pair<Integer,String>>();

        @Override
        protected void setup(Context context) throws IOException,InterruptedException {
            Configuration conf = context.getConfiguration();
            this.N = conf.getInt("N", 10);
        }

        @Override
        public void reduce(NullWritable key, Iterable<TextArrayWritable> values, Context context) throws IOException, InterruptedException {
            // TODO
            //Because Mapper's output key is a NullWritable, all of the output will send to a single reducer
            for (TextArrayWritable val:values) {
                Text[] pair = (Text[]) val.toArray();
                String word = pair[0].toString();
                Integer count = Integer.parseInt(pair[1].toString());
                titleCountMap.add(new Pair<Integer,String>(count,word));
            }
            if (titleCountMap.size() > N) {
                titleCountMap.remove(titleCountMap.first());
            }
            for (Pair<Integer,String> item:titleCountMap) {
                Text word = new Text(item.second);
                IntWritable count = new IntWritable(item.first);
                context.write(word, count);
            }
        }
    }

}

// >>> Don't Change
class Pair<A extends Comparable<? super A>,
        B extends Comparable<? super B>>
        implements Comparable<Pair<A, B>> {

    public final A first;
    public final B second;

    public Pair(A first, B second) {
        this.first = first;
        this.second = second;
    }

    public static <A extends Comparable<? super A>,
            B extends Comparable<? super B>>
    Pair<A, B> of(A first, B second) {
        return new Pair<A, B>(first, second);
    }

    @Override
    public int compareTo(Pair<A, B> o) {
        int cmp = o == null ? 1 : (this.first).compareTo(o.first);
        return cmp == 0 ? (this.second).compareTo(o.second) : cmp;
    }

    @Override
    public int hashCode() {
        return 31 * hashcode(first) + hashcode(second);
    }

    private static int hashcode(Object o) {
        return o == null ? 0 : o.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Pair))
            return false;
        if (this == obj)
            return true;
        return equal(first, ((Pair<?, ?>) obj).first)
                && equal(second, ((Pair<?, ?>) obj).second);
    }

    private boolean equal(Object o1, Object o2) {
        return o1 == o2 || (o1 != null && o1.equals(o2));
    }

    @Override
    public String toString() {
        return "(" + first + ", " + second + ')';
    }
}
// <<< Don't Change