Hadoop3：MapReduce中Reduce阶段自定义OutputFormat逻辑

一、情景描述

我们知道，在MapTask阶段开始时，需要InputFormat来读取数据
而在ReduceTask阶段结束时，将处理完成的数据，输出到磁盘，此时就要用到OutputFormat

在之前的程序中，我们都没有设置过这部分配置
所以，采用的是默认输出格式：TextOutputFormat

在实际工作中，我们的输出不一定是到磁盘，可能是输出到MySQL、HBase等

那么，如何实现自定义的OutputFormat？

二、案例

1、源数据

http://www.baidu.com
http://www.google.com
http://cn.bing.com
http://www.atguigu.com
http://www.sohu.com
http://www.baidu.com
http://www.sina.com
http://www.sin2a.com
http://www.baidu.com
http://www.sin2desa.com
http://www.sindsafa.com

2、需求分析

过滤输入的log日志，包含atguigu的网站输出到e:/atguigu.log，不包含atguigu的网站输出到e:/other.log。

3、代码实现

LogMapper.java

package com.atguigu.mapreduce.outputformat;import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;import java.io.IOException;public class LogMapper extends Mapper<LongWritable, Text,Text, NullWritable> {@Overrideprotected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {// http://www.baidu.com//http://www.google.com// (http://www.google.com, NullWritable)// 不做任何处理context.write(value, NullWritable.get());}
}

LogReducer.java

package com.atguigu.mapreduce.outputformat;import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;import java.io.IOException;public class LogReducer extends Reducer<Text, NullWritable, Text, NullWritable> {@Overrideprotected void reduce(Text key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {// http://www.baidu.com// http://www.baidu.com// 防止有相同数据，丢数据for (NullWritable value : values) {context.write(key, NullWritable.get());}}
}

LogRecordWriter.java

package com.atguigu.mapreduce.outputformat;import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;import java.io.IOException;public class LogRecordWriter extends RecordWriter<Text, NullWritable> {private  FSDataOutputStream atguiguOut;private  FSDataOutputStream otherOut;public LogRecordWriter(TaskAttemptContext job) {// 创建两条流try {FileSystem fs = FileSystem.get(job.getConfiguration());atguiguOut = fs.create(new Path("D:\\hadoop\\atguigu.log"));otherOut = fs.create(new Path("D:\\hadoop\\other.log"));} catch (IOException e) {e.printStackTrace();}}@Overridepublic void write(Text key, NullWritable value) throws IOException, InterruptedException {String log = key.toString();// 具体写if (log.contains("atguigu")){atguiguOut.writeBytes(log+"\n");}else {otherOut.writeBytes(log+"\n");}}@Overridepublic void close(TaskAttemptContext context) throws IOException, InterruptedException {// 关流IOUtils.closeStream(atguiguOut);IOUtils.closeStream(otherOut);}
}

LogOutputFormat.java

package com.atguigu.mapreduce.outputformat;import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.RecordWriter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import java.io.IOException;public class LogOutputFormat extends FileOutputFormat<Text, NullWritable> {@Overridepublic RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {LogRecordWriter lrw = new LogRecordWriter(job);return lrw;}
}

LogDriver.java

package com.atguigu.mapreduce.outputformat;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
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;import java.io.IOException;public class LogDriver {public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {Configuration conf = new Configuration();Job job = Job.getInstance(conf);job.setJarByClass(LogDriver.class);job.setMapperClass(LogMapper.class);job.setReducerClass(LogReducer.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(NullWritable.class);job.setOutputKeyClass(Text.class);job.setOutputValueClass(NullWritable.class);//设置自定义的outputformatjob.setOutputFormatClass(LogOutputFormat.class);FileInputFormat.setInputPaths(job, new Path("D:\\input\\inputoutputformat"));//虽然我们自定义了outputformat，但是因为我们的outputformat继承自fileoutputformat//而fileoutputformat要输出一个_SUCCESS文件，所以在这还得指定一个输出目录FileOutputFormat.setOutputPath(job, new Path("D:\\hadoop\\output1111"));boolean b = job.waitForCompletion(true);System.exit(b ? 0 : 1);}
}

3、测试

三、总结

关键文件：
LogRecordWriter.java
LogOutputFormat.java
LogDriver.java

        //设置自定义的outputformatjob.setOutputFormatClass(LogOutputFormat.class);