电脑基础 · 2023年3月2日

大数据框架之Hadoop:MapReduce(三)MapReduce框架原理——OutputFormat数据输出

3.6.1OutputFormat接口实现类

OutputFormat是MapReduce输出的基类,所有实现MapReduce输出都实现了OutputFormat接口。下面我们介绍几种常见的OutputFormat实现类。

1、文本输出TextOutputFormat

默认的输出格式是TextOutputFormat,它把每条记录写为文本行。它的键和值可以是任意类型,疑问TextOutputFormat调用toString()方法把他们转换为字符串。

2、SequenceFileOutputFormat

将SequenceFileOutputFormat输出作为后续MapReduce任务的输入,这便是一种好的输出格式,因为它的格式紧凑,很容易被压缩

3、自定义OutputFormat

根据用户需求,自定义实现输出。

3.6.2自定义OutputFormat

1、使用场景

为了实现控制最终文件的输出路径和输出格式,可以自定义OutputFormat。

例如:要在一个MapReduce程序中根据数据的不同输出两类结果到不同的目录,这类灵活的输出需求可以通过自定义OutputFormat来实现。

2、自定义OUtputFormat步骤

(1)自定义一个类继承FileOutputFormat。

(2)改写RecordWriter,具体改写输出数据的方法write()。

3.6.3自定义OutputFormat案例实操

1、需求

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。

(1)输入数据

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

(2)期望输出数据

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

2、需求分析

大数据框架之Hadoop:MapReduce(三)MapReduce框架原理——OutputFormat数据输出

3、案例实操

(1)编写FilterMapper类

package com.cuiyf41.output;
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 FilterMapper extends Mapper<LongWritable, Text, Text, NullWritable> {
    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, NullWritable>.Context context) throws IOException, InterruptedException {
        // 写出
        context.write(value, NullWritable.get());
    }
}

(2)编写FilterReducer类

package com.cuiyf41.output;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
import java.io.IOException;
public class FilterReducer extends Reducer<Text, NullWritable, Text, NullWritable> {
    Text k = new Text();
    @Override
    protected void reduce(Text key, Iterable<NullWritable> values, Reducer<Text, NullWritable, Text, NullWritable>.Context context) throws IOException, InterruptedException {
        // 1 获取一行
        String line = key.toString();
        // 2 拼接
        line = line + "\r\n";
        // 3 设置key
        k.set(line);
        // 4 输出
        context.write(k, NullWritable.get());
    }
}

(3)自定义一个OutputFormat类

package com.atguigu.mapreduce.outputformat;
import java.io.IOException;
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;
public class FilterOutputFormat extends FileOutputFormat<Text, NullWritable>{
	@Override
	public RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext job)			throws IOException, InterruptedException {
		// 创建一个RecordWriter
		return new FilterRecordWriter(job);
	}
}

(4)编写RecordWriter类

package com.cuiyf41.output;
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 FilterRecordWriter extends RecordWriter<Text, NullWritable> {
    FSDataOutputStream atguiguOut = null;
    FSDataOutputStream otherOut = null;
    public FilterRecordWriter(TaskAttemptContext job) {
        // 1 获取文件系统
        FileSystem fs;
        try {
            fs = FileSystem.get(job.getConfiguration());
            // 2 创建输出文件路径
            Path atguiguPath = new Path("e:/atguigu.log");
            Path otherPath = new Path("e:/other.log");
            // 3 创建输出流
            atguiguOut = fs.create(atguiguPath);
            otherOut = fs.create(otherPath);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public void write(Text key, NullWritable value) throws IOException, InterruptedException {
        // 判断是否包含“atguigu”输出到不同文件
        if (key.toString().contains("atguigu")) {
            atguiguOut.write(key.toString().getBytes());
        } else {
            otherOut.write(key.toString().getBytes());
        }
    }
    @Override
    public void close(TaskAttemptContext context) throws IOException, InterruptedException {
        // 关闭资源
        IOUtils.closeStream(atguiguOut);
        IOUtils.closeStream(otherOut);
    }
}

(5)编写FilterDriver类

package com.cuiyf41.output;
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 FilterDriver {
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        // 输入输出路径需要根据自己电脑上实际的输入输出路径设置
        args = new String[] { "e:/input/log.txt", "e:/output2" };
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);
        job.setJarByClass(FilterDriver.class);
        job.setMapperClass(FilterMapper.class);
        job.setReducerClass(FilterReducer.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);
        // 要将自定义的输出格式组件设置到job中
        job.setOutputFormatClass(FilterOutputFormat.class);
        Path input = new Path(args[0]);
        Path output = new Path(args[1]);
        // 如果输出路径存在,则进行删除
        FileSystem fs = FileSystem.get(conf);
        if (fs.exists(output)) {
            fs.delete(output,true);
        }
        FileInputFormat.setInputPaths(job, input);
        // 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, output);
        boolean result = job.waitForCompletion(true);
        System.exit(result ? 0 : 1);
    }
}