自定义KeyValueTextInputFormat

hadoop0.20.2中的API进行了大幅度的重构，导致很多API变成了@Deprecated，而新的API又不全，所以新手学起来感觉很变扭，社区开发者还是建议用hadoop0.20.2的可以沿用老版的API，本着学习的态度，用新的API添加了KeyValueTextInputFormat这个在老版API中存在的类，实际上是对TextInputFormat进行了小幅的修改。

package cn.fnst.cspf.output;

import java.io.IOException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
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.Text;
import org.apache.hadoop.io.compress.CompressionCodec;
import org.apache.hadoop.io.compress.CompressionCodecFactory;
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;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;
import org.apache.hadoop.util.LineReader;

public class KeyValueInputFormat extends FileInputFormat<Text, Text>{
	
	protected static class KeyVRecordReader extends RecordReader<Text,Text>{
		
		private static final Log LOG = LogFactory.getLog(KeyVRecordReader.class);
		
		  private CompressionCodecFactory compressionCodecs = null;
		  private long start;
		  private long pos;
		  private long end;
		  private LineReader in;
		  private int maxLineLength;
		  private Text key = null;
		  private Text value = null;
		  private String separator = "\t";
		  
		
		@Override
		public void initialize(InputSplit genericSplit, TaskAttemptContext context)
				throws IOException, InterruptedException {
			
			FileSplit split = (FileSplit) genericSplit;
		    Configuration job = context.getConfiguration();
		    this.maxLineLength = job.getInt("mapred.linerecordreader.maxlength",
		                                    Integer.MAX_VALUE);
		    this.separator = job.get("key.value.separator.in.input.line", "\t");
		    start = split.getStart();
		    end = start + split.getLength();
		    final Path file = split.getPath();
		    compressionCodecs = new CompressionCodecFactory(job);
		    final CompressionCodec codec = compressionCodecs.getCodec(file);

		    FileSystem fs = file.getFileSystem(job);
		    FSDataInputStream fileIn = fs.open(split.getPath());
		    boolean skipFirstLine = false;
		    if (codec != null) {
		      in = new LineReader(codec.createInputStream(fileIn), job);
		      end = Long.MAX_VALUE;
		    } else {
		      if (start != 0) {
		        skipFirstLine = true;
		        --start;
		        fileIn.seek(start);
		      }
		      in = new LineReader(fileIn, job);
		    }
		    if (skipFirstLine) {  
		      start += in.readLine(new Text(), 0,
		                           (int)Math.min((long)Integer.MAX_VALUE, end - start));
		    }
		    this.pos = start;
			
		}

		@Override
		public synchronized void close() throws IOException {
			if(in!=null){
				in.close();
			}
		}

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

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

		@Override
		public float getProgress() throws IOException, InterruptedException {
			if (start == end) {
			      return 0.0f;
			    } else {
			      return Math.min(1.0f, (pos - start) / (float)(end - start));
			    }
		}


		@Override
		public boolean nextKeyValue() throws IOException, InterruptedException {
			Text line = new Text();
			if (key == null) {
			      key = new Text();
			    }
		    if (value == null) {
		      value = new Text();
		    }
		    int newSize = 0;
		    while (pos < end) {
		      newSize = in.readLine(line, maxLineLength,
		                            Math.max((int)Math.min(Integer.MAX_VALUE, end-pos),
		                                     maxLineLength));
//此处添加额外处理即可，其他地方与TextInputFormat一样。
		      if(null!=line){
		    	  String[] kv = line.toString().split(this.separator);
		    	  if(kv.length==2){
		    		  key.set("key:"+kv[0]);
		    		  value.set("value:"+kv[1]);
		    	  }else{
		    		  LOG.info("Skipped line has no separator");
		    		  key.set(line.toString());
		    		  value.set("");
		    	  }
		      }
		      if (newSize == 0) {
		        break;
		      }
		      pos += newSize;
		      if (newSize < maxLineLength) {
		        break;
		      }

		      LOG.info("Skipped line of size " + newSize + " at pos " + 
		               (pos - newSize));
		    }
		    if (newSize == 0) {
		      key = null;
		      value = null;
		      return false;
		    } else {
		      return true;
		    }
		}

		
	}

	@Override
	public RecordReader<Text, Text> createRecordReader(InputSplit split,
			TaskAttemptContext context) throws IOException,
			InterruptedException {
		return new KeyVRecordReader();
	}
	
	@Override
	  protected boolean isSplitable(JobContext context, Path file) {
	    CompressionCodec codec = 
	      new CompressionCodecFactory(context.getConfiguration()).getCodec(file);
	    return codec == null;
	  }
}

在看老版的API时，发现旧的KeyValueTextInputFormat的作者基本上都是拿算法自己写，hadoop源码的很多地方都是不会拿现成的api来用，都是自己定义，这样做对性能的可控性是很强，这也折射出国外程序员跟国内程序员的差异，国内提倡拿来主义，国外可能更强调创新精神吧。