Hadoop 入门 之 实践之wordcount

groupId: com.hmzhou.hadoop

Artifactid:wordcount

pom.xml

​

-- 1
<packaging>jar</packaging>

-- 2
<dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.8.5</version>
        </dependency>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-hdfs</artifactId>
            <version>2.8.5</version>
        </dependency>

        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>2.8.5</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>

    </dependencies>

Mapper 编写

​

public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

    // 注意泛型的对应关系
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        // 此处使用空格分割
        String[] strings = value.toString().split(" ");
        for (String s : strings) {
            context.write(new Text(s), new IntWritable(1));
        }
    }
}

Reducer编写

public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable> {

    @Override
    protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
        int count = 0;
        for (IntWritable v : values) {
            count += v.get();
        }

        context.write(key, new IntWritable(count));
    }
}

Wordcount main方法编写

​

public class WordCount {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration configuration = new Configuration();

        String[] otherArgs = new GenericOptionsParser(configuration, args).getRemainingArgs();
        if (otherArgs.length < 2) {
            System.err.println("Usage: wordcount <in> [<in>...] <out>");
            System.exit(2);
        }
        rmr(configuration, otherArgs[otherArgs.length - 1]);
        Job job = Job.getInstance(configuration, "WordsCount");
        job.setJarByClass(WordCount.class);

        job.setMapperClass(WordCountMapper.class);
        job.setCombinerClass(WordCountReducer.class);
        job.setReducerClass(WordCountReducer.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));

        if (job.waitForCompletion(true)) {
            cat(configuration, otherArgs[1] + "/part-r-00000");
            System.out.println("success");
        } else {
            System.out.println("fail");
        }
    }


    private static boolean rmr(Configuration configuration, String dirPath) throws IOException {
        boolean delResult = false;
        Path targetPath = new Path(dirPath);
        FileSystem fs = targetPath.getFileSystem(configuration);
        if (fs.exists(targetPath)) {

            delResult = fs.delete(targetPath, true);
            if (delResult) {
                System.out.println(targetPath + " has bean deleted successful.");
            } else {
                System.out.println(targetPath + " deletion failed.");
            }
        }

        return delResult;
    }

    private static void cat(Configuration configuration, String filePath) throws IOException {
        InputStream inputStream = null;
        Path file = new Path(filePath);
        FileSystem fileSystem = file.getFileSystem(configuration);
        try {
            inputStream = fileSystem.open(file);
            org.apache.hadoop.io.IOUtils.copyBytes(inputStream, System.out, 4096, true);
        } finally {
            if (inputStream != null) {
                org.apache.hadoop.io.IOUtils.closeStream(inputStream);
            }
        }
    }
}

配置执行参数

注意需要将对应的输入文件 wordcount.txt 推送到hdfs

hdfs -put wordcount.txt /wordcount/words/input/