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Hadoop版Helloworld之wordcount运行示例

2024-08-31 08:38:29   222人阅读

1.编写一个统计单词数量的java程序，并命名为wordcount.java，代码如下：

import java.io.IOException;import java.util.StringTokenizer;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;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 WordCount {  public static class TokenizerMapper       extends Mapper<Object, Text, Text, IntWritable>{    private final static IntWritable one = new IntWritable(1);    private Text word = new Text();    public void map(Object key, Text value, Context context                    ) throws IOException, InterruptedException {      StringTokenizer itr = new StringTokenizer(value.toString());      while (itr.hasMoreTokens()) {        word.set(itr.nextToken());        context.write(word, one);      }    }  }  public static class IntSumReducer       extends Reducer<Text,IntWritable,Text,IntWritable> {    private IntWritable result = new IntWritable();    public void reduce(Text key, Iterable<IntWritable> values,                       Context context                       ) throws IOException, InterruptedException {      int sum = 0;      for (IntWritable val : values) {        sum += val.get();      }      result.set(sum);      context.write(key, result);    }  }  public static void main(String[] args) throws Exception {    Configuration conf = new Configuration();    Job job = Job.getInstance(conf, "word count");    job.setJarByClass(WordCount.class);    job.setMapperClass(TokenizerMapper.class);    job.setCombinerClass(IntSumReducer.class);    job.setReducerClass(IntSumReducer.class);    job.setOutputKeyClass(Text.class);    job.setOutputValueClass(IntWritable.class);    FileInputFormat.addInputPath(job, new Path(args[0]));    FileOutputFormat.setOutputPath(job, new Path(args[1]));    System.exit(job.waitForCompletion(true) ? 0 : 1);  }}

2.声明java环境变量：

export JAVA_HOME=/usr/java/defaultexport PATH=${JAVA_HOME}/bin:${PATH}export HADOOP_CLASSPATH=${JAVA_HOME}/lib/tools.jar

注意：如果不声明以上环境变量，那么在以后运行时，将会收到错误提示：

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3.编译并创建jar包。

bin/hadoop com.sun.tools.javac.Main WordCount.javajar cf wc.jar WordCount*.class

4.运行第三步骤生成的wc.jar包。此时要注意，output文件夹不要手工创建，系统运行后会自动创建。

bin/hadoop jar wc.jar WordCount /user/root/wordcount/input /user/root/wordcount/output

正常运行结束后，会在outPut文件夹下生成part-r-00000及__SUCCESS两个文件，其中part-r-00000存储分析结果。运行命令：

bin/hadoop fs -cat /user/joe/wordcount/output/part-r-00000

即可查看分析结果，如下图所示：
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至此，本示例完成。

Hadoop版Helloworld之wordcount运行示例


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