我们要自定义输出时，首先继承两个抽象类，一个是 OutputFormat，一个是 RecordWriter
。前者是主要是创建RecordWriter，后者就是主要实现 write方法来将kv写入文件。

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1、需求
将reduce输出的KV中，如果key中包含特定字符串，则将其输出到一个文件中，剩下的KV则输出到另外的文件中。

2、源码
源数据

http://cn.bing.com
http://www.baidu.com
http://www.google.com
http://www.itstar.com
http://www.itstar1.com
http://www.itstar2.com
http://www.itstar3.com
http://www.baidu.com
http://www.sin2a.com
http://www.sin2a.comw.google.com
http://www.sin2desa.com
http://www.sin2desa.comw.google.com
http://www.sina.com
http://www.sindsafa.com
http://www.sohu.com

outputFormat

public class MyOutputFormat extends FileOutputFormat {

    @Override
    public RecordWriter getRecordWriter(TaskAttemptContext taskAttemptContext) throws IOException, InterruptedException {
        return new MyRecordWriter(taskAttemptContext);
    }
}

RecordWriter

public class MyRecordWriter extends RecordWriter {
    private FSDataOutputStream startOut;
    private FSDataOutputStream otherOut;

    public MyRecordWriter(TaskAttemptContext job) {
        try {
            FileSystem fs = FileSystem.get(job.getConfiguration());
            startOut = fs.create(new Path("G:\\test\\date\\A\\itstarlog\\logdir\\startout.log"));
            otherOut = fs.create(new Path("G:\\test\\date\\A\\itstarlog\\logdir\\otherout.log"));
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    @Override
    public void write(Text key, NullWritable value) throws IOException, InterruptedException {
        String line = key.toString();

        //如果key中包含itstar就写入到另外一个文件中
        if (line.contains("itstar")) {
            this.startOut.writeUTF(line);
        } else {
            this.otherOut.writeUTF(line);
        }
    }

    @Override
    public void close(TaskAttemptContext taskAttemptContext) throws IOException, InterruptedException {
        this.startOut.close();
        this.otherOut.close();
    }
}

mapper

public class MyOutputMapper extends Mapper {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        context.write(value, NullWritable.get());
    }
}

reducer

public class MyOutputReducer extends Reducer {
    Text k = new Text();

    @Override
    protected void reduce(Text key, Iterable values, Context context) throws IOException, InterruptedException {
        String line = key.toString();
        line = line + "\r\n";
        k.set(line);

        context.write(k, NullWritable.get());
    }
}

driver

ublic class MyDriver {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

        args = new String[]{"G:\\test\\date\\A\\itstarlog\\A\\other.log", "G:\\test\\date\\A\\itstarlog\\logresult\\"};

        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);

        job.setJarByClass(MyDriver.class);
        job.setMapperClass(MyOutputMapper.class);
        job.setReducerClass(MyOutputReducer.class);

        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);

        //自定义输出的实现子类，也是继承FileOutputFormat
        job.setOutputFormatClass(MyOutputFormat.class);

        FileInputFormat.setInputPaths(job, new Path(args[0]));
        //这个路径输出的是job的执行成功successs文件的输出路径
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);
    }
}