Question

我最近安装了新的Hadoop 2.2。我以前写过一个简单的Word Count MapReduce程序，它曾经在CDH4上轻松工作。但是现在，我对所有org.apache.hadoop.mapreduce导入都有问题。有人能告诉我出口哪个罐子来修复这些进口吗？代码如下，以防有人需要指出我需要做的更改，以确保它在Hadoop 2.2中运行。

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

我在以下地点找到了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，我必须将以下内容添加到pom.xml中，然后干净地构建以便能够在Java中找到Mapper和Reducer类：

<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>

现在以下内容不会抛出错误：

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

Answer 3

如果您只是在Hadoop 2.2中查找相应JAR的位置，请查看share/hadoop/{common,hdfs,mapreduce}下的内容。您将找到以-2.2.0.jar结尾的文件，这些文件很可能就是您要找的。

除非您安装了与Hadoop 1.x结构匹配的“MR1”版本，否则它应与CDH4中的相同。

Answer 4

使用此链接查找您需要的任何JAR文件

下载它们，右键单击您的项目转到构建路径＆gt;配置构建路径＆gt;添加外部JAR

Apache Hadoop 2.2中的org.apache.hadoop.mapreduce导入问题

4 个答案: