OutputFormat

OutputFormat是MapReduce输出的基类，所有实现MapReduce输出都实现了OutputFormat接口。

常见的OutputFormat实现类如下所示，在IDEA中 按下 Ctrl + H 查看

自定义OutputFormat

输入文件：web_logs.txt

需求：将其中包含 mahe 字符串的网站，输出到一个文件中，其他不包含的去重后输出数据到另一个文件中

Mapper类

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> {

    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, NullWritable>.Context context) throws IOException, InterruptedException {

        // 不做任何处理
        context.write(value, NullWritable.get());
    }
}

Reducer类

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> {

    @Override
    protected void reduce(Text key, Iterable<NullWritable> values, Reducer<Text, NullWritable, Text, NullWritable>.Context context) throws IOException, InterruptedException {
        // 循环所有
        // 如果全部去重的话，直接输出就好了，因为key默认就是不重复的
        for (NullWritable val : values) {
            context.write(key, val);
            if (!key.toString().contains("mahe")){
                break;
            }
        }
    }
}

OutputFormat类

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;

/**
 * 这里的泛型是Reducer的输出类型
 */
public class LogOutputFormat extends FileOutputFormat<Text, NullWritable> {

    @Override
    public RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException {

        // 这里需要给LogRecordWriter类写一个构造方法，然后让这个类和job有关联
        return new LogRecordWriter(job);
    }
}

RecordWriter类

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;

/**
 * 这里也是Reducer输出的类型
 */
public class LogRecordWriter extends RecordWriter<Text, NullWritable> {

    private FSDataOutputStream maheOut;
    private FSDataOutputStream otherOut;

    public LogRecordWriter(TaskAttemptContext job) {

        try {
            // 创建两条流
            FileSystem fs = FileSystem.get(job.getConfiguration());

            maheOut = fs.create(new Path("D:\\output\\mahe.log"));
            otherOut = fs.create(new Path("D:\\output\\other.log"));
        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }

    @Override
    public void write(Text key, NullWritable value) throws IOException, InterruptedException {
        // 具体写的操作

        String log = key.toString() + "\n";
        if (log.contains("mahe")){
            maheOut.write(log.getBytes());
        }else{
            otherOut.write(log.getBytes());
        }

    }

    @Override
    public void close(TaskAttemptContext context) throws IOException, InterruptedException {
        // 关流
        IOUtils.closeStream(maheOut);
        IOUtils.closeStream(otherOut);
    }
}

Driver类

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, InterruptedException, ClassNotFoundException {
        // 1.获取job
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);

        // 2.设置jar包路径
        job.setJarByClass(LogDriver.class);

        // 3.关联mapper和reducer
        job.setMapperClass(LogMapper.class);
        job.setReducerClass(LogReducer.class);

        // 4.设置map输出的KV类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);

        // 5.设置最终输出的KV类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);

        // 设置OutputFormat
        job.setOutputFormatClass(LogOutputFormat.class);

        // 6.设置输入路径和输出路径
        FileInputFormat.setInputPaths(job, new Path("C:\\Users\\MaHe666\\Desktop\\web_logs.txt"));
        // 这里的路径是个文件夹
        FileOutputFormat.setOutputPath(job, new Path("D:\\output"));

        // 7.提交job
        // 源码当中用的就是 waitForCompletion()，该方法中已经有submit()了
        boolean result = job.waitForCompletion(true);
        System.exit(result ? 0 : 1);
    }
}