Apache Hadoop 2.2中的org.apache.hadoop.mapreduce導入問題

Question

我最近安裝了新的Hadoop 2.2。 我以前寫過一個簡單的Word Count MapReduce程序，它曾經在CDH4上輕松工作。 但是現在，我對所有org.apache.hadoop.mapreduce導入都有問題。 有人能告訴我出口哪個罐子來修復這些進口嗎？ 代碼如下，以防有人需要指出我需要做出的更改，以確保它在Hadoop 2.2中運行。

import java.io.IOException;
import java.lang.InterruptedException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

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;

public class MapRWordCount {
    private final static IntWritable ONE = new IntWritable(1);
    private final static Pattern WORD = Pattern.compile("\\w+");

    public static class WordCountMapper 
            extends Mapper<LongWritable, Text, Text, IntWritable> {
        private final Text word = new Text();

        @Override
        public void map(LongWritable key, Text value, Context context) 
                throws IOException, InterruptedException {

            String valueString = value.toString();
            Matcher matcher = WORD.matcher(valueString);
            while (matcher.find()) {
                word.set(matcher.group().toLowerCase());
                context.write(word, ONE);
            }
        }
    }

    public static class WordCountReducer 
            extends Reducer<Text, IntWritable, Text, IntWritable> {
        private final IntWritable totalCount = new IntWritable();

        @Override
        public void reduce(Text key, Iterable<IntWritable> values, Context context) 
                throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable value : values) {
                sum += value.get();
            }
            totalCount.set(sum);
            context.write(key, totalCount);
        }
    }

    public static void main(String[] args) 
            throws IOException, ClassNotFoundException, InterruptedException {

        if (args.length != 2) {
            System.err.println("Usage: MapRWordCount <input_path> <output_path>");
            System.exit(-1);
        }

        Job job = new Job();
        job.setJarByClass(MapRWordCount.class);
        job.setJobName("MapReduce Word Count");

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

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

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

        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }

}

Answer 1

我在以下位置找到了JAR：

$HADOOP_HOME/share/hadoop/common/hadoop-common-2.2.0.jar
$HADOOP_HOME/share/hadoop/mapreduce/hadoop-mapreduce-client-core-2.2.0.jar

Answer 2

在maven中，我不得不將以下內容添加到pom.xml中，然后干凈地構建以便能夠在Java中找到Mapper和Reducer類：

<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-common</artifactId>
    <version>2.2.0</version>
</dependency>
<dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-mapreduce-client-core</artifactId>
    <version>2.2.0</version>
</dependency>

現在以下內容不會拋出錯誤：

import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;

Answer 3

如果你只是在Hadoop 2.2中尋找合適的JAR的位置，那么請查看share/hadoop/{common,hdfs,mapreduce} 。 您將找到以-2.2.0.jar結尾的文件，這些文件很可能是您要找的。

這應該與CDH4中的相同，除非您安裝了與Hadoop 1.x結構匹配的“MR1”版本。

Answer 4

使用此鏈接查找您需要的任何JAR文件

下載它們，右鍵單擊您的項目轉到構建路徑>配置構建路徑>添加外部JAR