Hadoop WordCount程序

一、把所有Hadoop的依赖jar包导入buildpath，不用一个一个调，都导一遍就可以，因为是一个工程，所以覆盖是没有问题的

二、写wordcount程序

1.工程目录结构如下：

2.写mapper程序：

package mapreduce;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
/**
 * LongWritable想当于long，这个是Hadoop特有的类型，因为是要网络间通信远程执行的，所以需要序列化，这个封装类型的序列化效果更好
 * Text等于String
 * @author Q
 *
 */
public class WordCountMapper extends Mapper<LongWritable, Text, Text, LongWritable>{
    @Override
    protected void map(LongWritable key, Text value,
            Mapper<LongWritable, Text, Text, LongWritable>.Context context)
            throws IOException, InterruptedException {
        // key为字符偏移量 value为一行的内容
        String line = value.toString();
        String[] words = line.split(" ");
        //发送 <key,1>键值对到reducer
        for(String word:words){
            context.write(new Text(word), new LongWritable());
        }
    }

}

2.写reducer程序

package mapreduce;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class WordCountReducer extends Reducer<Text, LongWritable, Text, LongWritable>{
    @Override
    protected void reduce(Text key, Iterable<LongWritable> values,
            Reducer<Text, LongWritable, Text, LongWritable>.Context context)
            throws IOException, InterruptedException {
        long sub=;
        //接收到<key,value>键值对，此时key为单词，value是一个迭代器，可以看成例如：<"hello",List{1,1,1,1,1}>
        for(LongWritable value:values){
            sub+=value.get();
        }
        context.write(key, new LongWritable(sub));

    }

}

3.写main函数

package mapreduce;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class WordCount {
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        // 获取job对象，用来提交MapReduce任务
        Job job = Job.getInstance(conf);
        // 通过class路径设置jar
        job.setJarByClass(WordCount.class);
        // 设置mapper和reducer类
        job.setMapperClass(WordCountMapper.class);
        job.setReducerClass(WordCountReducer.class);
        // 设置mapper的输出键值对的类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);
        // 设置reducer的输出键值对
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        // 输入输出文件的路径
        FileInputFormat.setInputPaths(job, new Path("hdfs://hadoop1:9000/wordcount/data/"));
        FileOutputFormat.setOutputPath(job, new Path("hdfs://hadoop1:9000/wordcount/output1"));
        //提交任务
        job.waitForCompletion(true);
    }

}

4.将工程打包成jar文件传到Linux平台上

打包：鼠标放在工程上右键---》点击export--》java--》JAE File

Linux上运行jar包的命令是

hadoop jar wordcount.jar mapreduce.WordCount  有两个参数，第一个参数是你打包的jar的名字，第二个参数是你的main函数的全限定名