Hadoop RecordReader

自定义RecordReader
步骤：
1）继承抽象类RecordReader，实现RecordReader的一个实例
2）实现自定义InputFormat类，重写InputFormat中的createRecordReader（）方法，返回值是自定义的RecordReader实例
3）配置job.setInputFormatClass（）设置自定义的InputFormat实例

RecordReader例子
应用场景：
数据：
10
20
30
40
50
60
70
要求：分别计算奇数行与偶数行数据之和
奇数行总和：10+30+50+70=160
偶数行总和：20+40+60=120
MyRecordReader.java

package com.recordreader;

import java.io.IOException;

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.LongWritable;
import org.apache.hadoop.io.Text;
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 org.apache.hadoop.util.LineReader;

public class MyRecordReader extends RecordReader {
    private long start ;
    private long end ;
    private long pos ;//表示行号
    private FSDataInputStream fin = null ;
    private LongWritable key = null ;
    private Text value = null ;
    private LineReader reader = null ;
    @Override
    public void close() throws IOException {
        fin.close() ;
    }

    @Override
    public LongWritable getCurrentKey() throws IOException,
            InterruptedException {
        return key;
    }

    @Override
    public Text getCurrentValue() throws IOException, InterruptedException {
        return value;
    }

    @Override
    public float getProgress() throws IOException, InterruptedException {
        return 0;
    }

    @Override
    public void initialize(InputSplit inputSplit, TaskAttemptContext context)
            throws IOException, InterruptedException {
        FileSplit fileSplit = (FileSplit)inputSplit ;
        start = fileSplit.getStart() ;
        end = start + fileSplit.getLength() ;

        Configuration conf = context.getConfiguration() ;
        Path path = fileSplit.getPath() ;
        FileSystem fs = path.getFileSystem(conf) ;
        fin = fs.open(path) ;
        fin.seek(start) ;
        reader = new LineReader(fin) ;
        pos = 1 ;

    }

    @Override
    public boolean nextKeyValue() throws IOException, InterruptedException {
        if(key == null){
            key = new LongWritable() ;
        }
        key.set(pos) ;

        if(value == null){
            value = new Text() ;
        }

        if(reader.readLine(value) ==0){
            return false ;
        }

        pos++ ;
        return true ;
    }

}

MyFileInputFormat.java

package com.recordreader;

import java.io.IOException;

import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;

public class MyFileInputFormat extends FileInputFormat {

    @Override
    public RecordReader createRecordReader(InputSplit arg0,
            TaskAttemptContext arg1) throws IOException, InterruptedException {
        return new MyRecordReader();
    }

    @Override
    protected boolean isSplitable(JobContext context, Path filename) {

        return false ;
    }



}

MyMapper.java

package com.recordreader;

import java.io.IOException;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class MyMapper extends Mapper<LongWritable, Text, LongWritable, Text> {

    @Override
    protected void map(LongWritable key, Text value,Context context)
            throws IOException, InterruptedException {
        context.write(key, value) ;
    }

}

MyPartitioner.java

package com.recordreader;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Partitioner;

public class MyPartitioner extends Partitioner<LongWritable, Text> {

    @Override
    public int getPartition(LongWritable key, Text value, int numPartitions) {
        if(key.get() % 2 == 0){
            key.set(1) ;
            return 1 ;
        }else{
            key.set(0) ;
            return 0 ;
        }

    }

}

MyReducer.java

package com.recordreader;

import java.io.IOException;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class MyReducer extends Reducer<LongWritable, Text, Text, IntWritable> {

    @Override
    protected void reduce(LongWritable key, Iterable value,Context context)
            throws IOException, InterruptedException {
        int sum = 0 ;
        for(Text val : value){
            sum += Integer.valueOf(val.toString()) ;
        }
        Text writeKey = new Text() ;
        IntWritable writeValue = new IntWritable() ;

        if(key.get() == 0){
            writeKey.set("奇数行之和：") ;
        }else{
            writeKey.set("偶数行之和：") ;
        }

        writeValue.set(sum) ;
        context.write(writeKey, writeValue) ;
    }

}

TestRecordReader.java

package com.recordreader;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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 org.apache.hadoop.mapreduce.lib.reduce.IntSumReducer;
import org.apache.hadoop.util.GenericOptionsParser;

public class TestRecordReader {
    public static void main(String args[]) throws Exception{
        Configuration conf = new Configuration();
        String[] otherArgs = new GenericOptionsParser(conf, args)
                .getRemainingArgs();
        if (otherArgs.length != 2) {
            System.err.println("Usage: wordcount  ");
            System.exit(2);
        }
        Job job = new Job(conf, "word count");
        job.setJarByClass(TestRecordReader.class);
        job.setMapperClass(MyMapper.class);

        job.setReducerClass(MyReducer.class);
        job.setPartitionerClass(MyPartitioner.class) ;
        job.setNumReduceTasks(2) ;
        job.setInputFormatClass(MyFileInputFormat.class) ;

//      job.setOutputKeyClass(Text.class);
//      job.setOutputValueClass(IntWritable.class);


        FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
        FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}