【Hadoop离线基础总结】MapReduce自定义InputFormat和OutputFormat案例

MapReduce自定义InputFormat和OutputFormat案例

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自定义InputFormat 合并小文件

• 需求
  
  无论hdfs还是mapreduce，存放小文件会占用元数据信息，白白浪费内存，实践中，又难免面临处理大量小文件的场景

• 优化小文件的三种方式
  
  1.在数据采集的时候，就将小文件或小批数据合成大文件再上传HDFS
  
  2.在业务处理之前，在HDFS上使用mapreduce程序对小文件进行合并
  
  3.在mapreduce处理时，可采用combineInputFormat提高效率

• 用代码实现第二种方式

自定义InputFormat

package cn.itcast.demo3;
import jdk.nashorn.internal.ir.Splittable;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.*;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import java.io.IOException;
import java.util.List;
public class MyInputFormat extends FileInputFormat<NullWritable, BytesWritable> {
    @Override
    public RecordReader<NullWritable, BytesWritable> createRecordReader(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException {
        MyRecordReader myRecordReader = new MyRecordReader();
        myRecordReader.initialize(split, context);
        return myRecordReader;
    }
    /**
     * 表示我们的文件是否可切分
     * 返回false表示我们的文件不可切分，读取文件时会一次性将文件内容全部读取出来
     *
     * @param context
     * @param filename
     * @return
     */
    @Override
    protected boolean isSplitable(JobContext context, Path filename) {
        return false;
    }
}

自定义RecordReader

package cn.itcast.demo3;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import java.io.IOException;
import java.io.InputStream;
public class MyRecordReader extends RecordReader<NullWritable, BytesWritable> {
    //定义文件切片
    private FileSplit fileSplit;
    //定义文件configuration
    private Configuration configuration;
    //定义v2
    private BytesWritable bytesWritable = new BytesWritable();
    //定义下面nextKeyValue返回值为false
    private boolean nextKeyValue = false;
    /**
     * 初始化方法
     * 这里可以拿到文件切片，也就意味着可以拿到文件，将文件转换为字节数组
     *
     * @param split
     * @param context
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public void initialize(InputSplit split, TaskAttemptContext context) throws IOException, InterruptedException {
        //获取文件切片
        this.fileSplit = (FileSplit) split;
        //获取文件Configuration
        this.configuration = context.getConfiguration();
    }
    /**
     * 返回true，表示文件读取完成，不会再往下继续读取文件
     * 返回false，表示会继续往下读取文件
     *
     * @return
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
        if (!nextKeyValue) {
            //根据文件的切片，将文件的内容全部读取出来，封装到BytesWritable中
            byte[] fileContent = new byte[(int) fileSplit.getLength()];
            //获取文件切片路径
            Path path = fileSplit.getPath();
            //获取文件系统
            FileSystem fileSystem = path.getFileSystem(configuration);
            //打开文件输入流
            FSDataInputStream inputStream = fileSystem.open(path);
            //将输入流转到字节数组中
            IOUtils.readFully(inputStream, fileContent, 0, (int) fileSplit.getLength());
            bytesWritable.set(fileContent, 0, fileContent.length);
            //将读取文件的标识设置为true，表示文件已经读取完成，不需要继续读取
            nextKeyValue = true;
            IOUtils.closeStream(inputStream);
            return nextKeyValue;
        }
        return false;
    }
    /**
     * 用来返回k1的值
     *
     * @return
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public NullWritable getCurrentKey() throws IOException, InterruptedException {
        return NullWritable.get();
    }
    /**
     * 用来返回v1的值
     *
     * @return
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public BytesWritable getCurrentValue() throws IOException, InterruptedException {
        return bytesWritable;
    }
    /**
     * 不太需要注意，就是用来读取运行进度的
     *
     * @return
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public float getProgress() throws IOException, InterruptedException {
        return nextKeyValue ? 1.0F : 0.0F;
    }
    /**
     * 用来读取完后释放资源的，了解即可
     *
     * @throws IOException
     */
    @Override
    public void close() throws IOException {
    }
}

定义一个Mapper类

package cn.itcast.demo3;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import java.io.IOException;
public class MyMapperInput extends Mapper<NullWritable, BytesWritable, Text, BytesWritable> {
    @Override
    protected void map(NullWritable key, BytesWritable value, Context context) throws IOException, InterruptedException {
        //获取文件切片
        FileSplit inputSplit = (FileSplit) context.getInputSplit();
        //获取文件名称
        String name = inputSplit.getPath().getName();
        //输出k2,v2
        context.write(new Text(name), value);
    }
}

程序main函数入口

package cn.itcast.demo3;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.BytesWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
public class OwnInputFormatMain extends Configured implements Tool {
    @Override
    public int run(String[] args) throws Exception {
        //创建job对象
        Job job = Job.getInstance(super.getConf(), "ownInputFormat");
        //输入数据，设置输入路径，注意这里是自动以的InputFormat
        job.setInputFormatClass(MyInputFormat.class);
        MyInputFormat.addInputPath(job, new Path("file:////Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义inputformat_小文件合并/input"));
        //自定义map逻辑
        job.setMapperClass(MyMapperInput.class);
        //设置k2,v2输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(BytesWritable.class);
        //虽然没有reducer，但是不设置reduce输出类型，默认的是<LongWritable,Text>
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(BytesWritable.class);
		//输出数据，设置输出路径
        job.setOutputFormatClass(SequenceFileOutputFormat.class);
        SequenceFileOutputFormat.setOutputPath(job,new Path("file:////Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义inputformat_小文件合并/sequence_output"));
        //提交任务到集群
        boolean b = job.waitForCompletion(true);
        return b ? 0 : 1;
    }
    public static void main(String[] args) throws Exception {
        int run = ToolRunner.run(new Configuration(), new OwnInputFormatMain(), args);
        System.exit(run);
    }
}

---

自定义OutputFormat 将一个文件中的数据分发到不同文件

• 需求
  
  将订单的好评与差评区分开来，并将最终的数据发送到不同的文件夹下面去，其中数据第九个字段表示好评，中评，差评。0：好评，1：中评，2：差评

• 代码实现

自定义OutputFormat

package cn.itcast.demo4;
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.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 MyOutputFormat extends FileOutputFormat<Text, NullWritable> {
    @Override
    public RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext context) throws IOException, InterruptedException {
        //从这个方法里就可以获取一个configuration
        Configuration configuration = context.getConfiguration();
        //获取文件系统
        FileSystem fileSystem = FileSystem.get(configuration);
        //设置好评文件的输出路径
        Path goodComment = new Path("/Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义outputformat/myGoodComment/1.txt");
        //设置差评文件的输出路径
        Path badComment = new Path("/Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义outputformat/myBadComment/1.txt");
        //获取文件输出流
        FSDataOutputStream fsDataOutputStream = fileSystem.create(goodComment);
        FSDataOutputStream fsDataOutputStream1 = fileSystem.create(badComment);
        MyRecordWriter myRecordWriter = new MyRecordWriter(fsDataOutputStream, fsDataOutputStream1);
        return myRecordWriter;
    }
}

自定义RecordWriter

package cn.itcast.demo4;
import org.apache.hadoop.fs.FSDataOutputStream;
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 MyRecordWriter extends RecordWriter<Text, NullWritable> {
    //使用无参和带参构造调用goodStream和badStream
    private FSDataOutputStream goodStream;
    private FSDataOutputStream badStream;
    public MyRecordWriter() {
    }
    public MyRecordWriter(FSDataOutputStream goodStream, FSDataOutputStream badStream) {
        this.goodStream = goodStream;
        this.badStream = badStream;
    }
    /**
     * 这个write方法就是往外写出去数据
     *
     * @param key   可以根据这个key，来判断文件究竟往哪个目录下写
     * @param value
     * @throws IOException
     * @throws InterruptedException
     */
    @Override
    public void write(Text key, NullWritable value) throws IOException, InterruptedException {
        //分割导入的数据
        String[] split = key.toString().split("\t");
        //获取评论状态    0：好评    1：中评    2：差评;
        //判断评论状态,如果小于等于1则写到好评文件中，否则写到差评文件中
        if (Integer.parseInt(split[9]) <= 1) {
            goodStream.write(key.toString().getBytes());
            goodStream.write("\r\n".getBytes());
        } else {
            badStream.write(key.toString().getBytes());
            badStream.write("\r\n".getBytes());
        }
    }
    @Override
    public void close(TaskAttemptContext taskAttemptContext) throws IOException, InterruptedException {
        IOUtils.closeStream(goodStream);
        IOUtils.closeStream(badStream);
    }
}

定义一个Mapper类

package cn.itcast.demo4;
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 MyOutputMapper extends Mapper<LongWritable, Text, Text, NullWritable> {
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        context.write(value, NullWritable.get());
    }
}

程序main函数入口

package cn.itcast.demo4;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
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.TextInputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
public class MyOutputMain extends Configured implements Tool {
    @Override
    public int run(String[] args) throws Exception {
        //创建job对象
        Job job = Job.getInstance(super.getConf(), "OutputFormat");
        //输入数据，设置输入路径
        job.setInputFormatClass(TextInputFormat.class);
        TextInputFormat.setInputPaths(job, new Path("file:////Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义outputformat/input/ordercomment.csv"));
        //自定义map逻辑
        job.setMapperClass(MyOutputMapper.class);
        //设置k2,v2输出类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);
        //输出数据，设置输出路径，这里的输出路径不是真正的输出路径
        job.setOutputFormatClass(MyOutputFormat.class);
        MyOutputFormat.setOutputPath(job, new Path("file:////Volumes/赵壮备份/大数据离线课程资料/5.大数据离线第五天/自定义outputformat/output"));
        //提交任务至集群
        boolean b = job.waitForCompletion(true);
        return b ? 0 : 1;
    }
    public static void main(String[] args) throws Exception {
        int run = ToolRunner.run(new Configuration(), new MyOutputMain(), args);
        System.exit(run);
    }
}