手写WordCount示例编写

cd /export/servers

vim wordcount.txt

hello,world,hadoop
hive,sqoop,flume,hello
kitty,tom,jerry,world
hadoop

hdfs dfs -mkdir /wordcount/
hdfs dfs -put wordcount.txt /wordcount/

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;

public class WordCountMapper extends Mapper<LongWritable,Text,Text,LongWritable> {
    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String line = value.toString();
        String[] split = line.split(",");
        for (String word : split) {
            context.write(new Text(word),new LongWritable(1));
        }

    }
}

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

public class WordCountReducer extends Reducer<Text,LongWritable,Text,LongWritable> {
    /**
     * 自定义reduce逻辑
     * 所有的key都是单词，所有的values都是单词出现的次数
     * @param key
     * @param values
     * @param context
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
        long count = 0;
        for (LongWritable value : values) {
            count += value.get();
        }
        context.write(key,new LongWritable(count));
    }
}

public class JobMain extends Configured implements Tool {
@Override
public int run(String[] args) throws Exception {
    Job job = Job.getInstance(super.getConf(), JobMain.class.getSimpleName());
    //打包到集群上面运行时候，必须要添加以下配置，指定程序的main函数
    job.setJarByClass(JobMain.class);
    //第一步：读取输入文件解析成key，value对
    job.setInputFormatClass(TextInputFormat.class);
    TextInputFormat.addInputPath(job,new Path("hdfs://192.168.100.129:8020/wordcount"));

    //第二步：设置mapper类
    job.setMapperClass(WordCountMapper.class);
    //设置map阶段完成之后的输出类型
    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(LongWritable.class);
    //第三步，第四步，第五步，第六步，省略
    //第七步：设置reduce类
    job.setReducerClass(WordCountReducer.class);
    //设置reduce阶段完成之后的输出类型
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(LongWritable.class);
    //第八步：设置输出类以及输出路径
    job.setOutputFormatClass(TextOutputFormat.class);
    TextOutputFormat.setOutputPath(job,new Path("hdfs://192.168.100.129:8020/wordcount_out"));
    boolean b = job.waitForCompletion(true);
    return b?0:1;
}

/**
 * 程序main函数的入口类
 * @param args
 * @throws Exception
 */
public static void main(String[] args) throws Exception {
    Configuration configuration = new Configuration();
    Tool tool  =  new JobMain();
    int run = ToolRunner.run(configuration, tool, args);
    System.exit(run);
}

hadoop jar hadoop_hdfs_operate-1.0-SNAPSHOT.jar cn.itcast.hdfs.demo1.JobMain