OutputFormat数据输出

相较于InputFormat，OutputFormat相对而言简单些.
OutPutFormat是MapReduce输出的基类，所有MapReduce输出都实现了OutputFormat接口.
1. 文本输出TextOutputFormat
默认的输出格式是TextOutputFormat，它把每条记录写成文本行.它的键值可以是任意类型，因为TextOutputFormat调用toString()方法把它们转换成字符串.
2. SequenceFileOutputFormat
将SequenceFileOutputFormat输出作为后续的MapReduce任务的输入，这是一种好的输入格式，因为它存储的是二进制格式，格式紧凑，易于压缩.
3. 自定义OutputFormat
（1）自定义一个类， 继承FileOutputFormat类
（2）自定义一个RecordWriter类，继承RecordWriter类，具体改写输出数据的方法write()
4. 代码实现

OutputFormat类

package 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 OPFormat extends FileOutputFormat<Text, NullWritable> {

    @Override
    public RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext context) throws IOException, InterruptedException {
        return new OPRecordWriter(context);
    }
}

RecordWriter类

package outputformat;

import org.apache.hadoop.conf.Configuration;
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 OPRecordWriter extends RecordWriter<Text, NullWritable> {
    private FSDataOutputStream google = null;
    private FSDataOutputStream other = null;

    public OPRecordWriter(TaskAttemptContext job) throws IOException {
        Configuration conf = job.getConfiguration();
        FileSystem fs = FileSystem.get(conf);
        Path gPath = new Path("i:\\op_output\\google");
        Path oPath = new Path("i:\\op_output\\other");
        google = fs.create(gPath);
        other = fs.create(oPath);
    }

    @Override
    public void write(Text text, NullWritable nullWritable) throws IOException, InterruptedException {
        if (text.toString().contains("google")) {
            google.write(text.getBytes());
            google.write("\n".getBytes());
        } else {
            other.write(text.getBytes());
            other.write("\n".getBytes());
        }
    }

    @Override
    public void close(TaskAttemptContext taskAttemptContext) throws IOException, InterruptedException {
        IOUtils.closeStream(google);
        IOUtils.closeStream(other);
    }
}

Mapper类

package 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 OPMapper extends Mapper<LongWritable, Text, Text, NullWritable> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        context.write(value, NullWritable.get());
    }
}

Reducer类

package 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 OPReducer extends Reducer<Text, NullWritable, Text, NullWritable> {
    @Override
    protected void reduce(Text key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
        for (NullWritable value : values) {
            context.write(key, NullWritable.get());
        }
    }
}

Driver类

package outputformat;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
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 OPDriver {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(conf);
        Path oPath = new Path("i:\\op_output");
        if (fs.exists(oPath)) {
            fs.delete(oPath, true);
        }

        Job job = Job.getInstance(conf);
        job.setJarByClass(OPDriver.class);
        job.setMapperClass(OPMapper.class);
        job.setReducerClass(OPReducer.class);

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

        job.setOutputFormatClass(OPFormat.class);
        FileInputFormat.addInputPath(job, new Path("i:\\op_input"));
        FileOutputFormat.setOutputPath(job, oPath);

        boolean result = job.waitForCompletion(true);
        System.exit(result ? 0 : 1);
    }
}