直接附代码，说明都在源码里了。
package com.hadoop.totalsort;
import java.io.IOException;
import java.util.ArrayList;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.SequenceFile;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.FileInputFormat;
import org.apache.hadoop.mapred.FileSplit;
import org.apache.hadoop.mapred.InputSplit;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.LineRecordReader;
import org.apache.hadoop.mapred.RecordReader;
import org.apache.hadoop.mapred.Reporter;
import org.apache.hadoop.util.IndexedSortable;
import org.apache.hadoop.util.QuickSort;
public class SamplerInputFormat extends FileInputFormat<Text, Text> {
static final String PARTITION_FILENAME = "_partition.lst";
static final String SAMPLE_SIZE = "terasort.partitions.sample";
private static JobConf lastConf = null;
private static InputSplit[] lastResult = null;
static class TextSampler implements IndexedSortable {
public ArrayList<Text> records = new ArrayList<Text>();
public int compare(int arg0, int arg1) {
Text right = records.get(arg0);
Text left = records.get(arg1);
return right.compareTo(left);
}
public void swap(int arg0, int arg1) {
Text right = records.get(arg0);
Text left = records.get(arg1);
records.set(arg0, left);
records.set(arg1, right);
}
public void addKey(Text key) {
records.add(new Text(key));
}
//将采集出来的key数据排序
public Text[] createPartitions(int numPartitions) {
int numRecords = records.size();
if (numPartitions > numRecords) {
throw new IllegalArgumentException("Requested more partitions than input keys (" + numPartitions +
" > " + numRecords + ")");
}
new QuickSort().sort(this, 0, records.size());
float stepSize = numRecords / (float) numPartitions; //采集的时候应该是采了100条记录,从10个分片查找的,此处再取numPartitions-1条
Text[] result = new Text[numPartitions - 1];
for (int i = 1; i < numPartitions; ++i) {
result[i - 1] = records.get(Math.round(stepSize * i));
}
return result;
}
}
public static void writePartitionFile(JobConf conf, Path partFile) throws IOException {
//前段代码从分片中采集数据，通过sampler.addKey存入TextSampler中的records数组
SamplerInputFormat inputFormat = new SamplerInputFormat();
TextSampler sampler = new TextSampler();
Text key = new Text();
Text value = new Text();
int partitions = conf.getNumReduceTasks(); // Reducer任务的个数
long sampleSize = conf.getLong(SAMPLE_SIZE, 100); // 采集数据-键值对的个数
InputSplit[] splits = inputFormat.getSplits(conf, conf.getNumMapTasks());// 获得数据分片
int samples = Math.min(10, splits.length);// 采集分片的个数 ,采集10个分片
long recordsPerSample = sampleSize / samples;// 每个分片采集的键值对个数
int sampleStep = splits.length / samples; // 采集分片的步长 ,总的分片个数/要采集的分片个数
long records = 0;
for (int i = 0; i < samples; i++) { //1...10分片数
RecordReader<Text, Text> reader = inputFormat.getRecordReader(splits[sampleStep * i], conf, null);
while (reader.next(key, value)) {
sampler.addKey(key); //将key值增加到sampler的records数组
records += 1;
if ((i + 1) * recordsPerSample <= records) { //目的是均匀采集各分片的条数，比如采集到第5个分片,那么记录条数应该小于5个分片应该的条数
break;
}
}
}
FileSystem outFs = partFile.getFileSystem(conf);
if (outFs.exists(partFile)) {
outFs.delete(partFile, false);
}
SequenceFile.Writer writer = SequenceFile.createWriter(outFs, conf, partFile, Text.class, NullWritable.class);
NullWritable nullValue = NullWritable.get();
for (Text split : sampler.createPartitions(partitions)) { //调用createPartitions方法，排序采集出来的数据，并取partitions条
writer.append(split, nullValue);
}
writer.close();
}
static class TeraRecordReader implements RecordReader<Text, Text> {
private LineRecordReader in;
private LongWritable junk = new LongWritable();
private Text line = new Text();
private static int KEY_LENGTH = 10;
public TeraRecordReader(Configuration job, FileSplit split) throws IOException {
in = new LineRecordReader(job, split);
}
public void close() throws IOException {
in.close();
}
public Text createKey() {
// TODO Auto-generated method stub
return new Text();
}
public Text createValue() {
return new Text();
}
public long getPos() throws IOException {
// TODO Auto-generated method stub
return in.getPos();
}
public float getProgress() throws IOException {
// TODO Auto-generated method stub
return in.getProgress();
}
public boolean next(Text arg0, Text arg1) throws IOException {
if (in.next(junk, line)) { //调用父类方法,将value值赋给key
// if (line.getLength() < KEY_LENGTH) {
arg0.set(line);
arg1.clear();
// } else {
// byte[] bytes = line.getBytes(); // 默认知道读取要比较值的前10个字节 作为key
// // 后面的字节作为value；
// arg0.set(bytes, 0, KEY_LENGTH);
// arg1.set(bytes, KEY_LENGTH, line.getLength() - KEY_LENGTH);
// }
return true;
} else {
return false;
}
}
}
@Override
public InputSplit[] getSplits(JobConf conf, int splits) throws IOException {
if (conf == lastConf) {
return lastResult;
}
lastConf = conf;
lastResult = super.getSplits(lastConf, splits);
return lastResult;
}
public org.apache.hadoop.mapred.RecordReader<Text, Text> getRecordReader(InputSplit arg0, JobConf arg1,
Reporter arg2) throws IOException {
return new TeraRecordReader(arg1, (FileSplit) arg0);
}
}
转载自：http://www.open-open.com/lib/view/open1381329062408.html