定义DoubleArray并将其作为value写入SequenceFile

1)上代码：

 /**
  * Created with IntelliJ IDEA.
  * User: hadoop
  * Date: 16-1-20
  * Time: 下午7:30
  * To change this template use File | Settings | File Templates.
  */
 import org.apache.hadoop.io.*;
 import java.util.*;
 public class DoubleWritableArray {
     public static class DoubleArray extends ArrayWritable{
       public DoubleArray(){
           super(DoubleWritable.class);
       }
        // public  DoubleWritable[] get(){return values;}

        public static double[] convert2double(DoubleWritable[] w){
             double[] value=new double[w.length];
             for (int i = 0; i < value.length; i++) {
                 value[i]=Double.valueOf(w[i].get());
             }
             return value;
         }

     }

     public static void main(String[]args){

         ArrayWritable aw=new ArrayWritable(DoubleWritable.class);
         aw.set(new DoubleWritable[] {new DoubleWritable(4.34),new DoubleWritable(6.56),
                 new DoubleWritable(9.56)});

         DoubleWritable[] values=(DoubleWritable[])aw.get();
         for(DoubleWritable val1:values){
             System.out.println(val1);
         }
         //与ArrayWritable相比，新定义的DoubleArray只是在调用构造函数的时候少写了DoubleWritable类而已
         DoubleArray d=new DoubleArray();
         d.set(new DoubleWritable[] {new DoubleWritable(4.34),new DoubleWritable(6.56),
                 new DoubleWritable(9.56)});

         double[] temp=DoubleArray.convert2double((DoubleWritable[])d.get())   ;
         for (double val:temp)
             System.out.println(val);

     }

 }

ArrayWritable作为reduce的输入的话，需要创建其子类，在子类中创建一个无参构造函数。

来源：http://grepcode.com/file/repo1.maven.org/maven2/org.jvnet.hudson.hadoop/hadoop-core/0.19.1-hudson-2/org/apache/hadoop/io/ArrayWritable.java#ArrayWritable.toArray%28%29

2）读取txt文件并将其以<long,DoubleArray>作为键值对的形式写入SequenceFile

 package convert;

 /**
  * Created with IntelliJ IDEA.
  * User: hadoop
  * Date: 16-1-19
  * Time: 下午3:09
  * To change this template use File | Settings | File Templates.
  */
 import java.io.IOException;
 import java.net.URI;

 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.io.DoubleWritable;
 import org.apache.hadoop.io.IOUtils;
 import org.apache.hadoop.io.IntWritable;
 import org.apache.hadoop.io.LongWritable;
 import org.apache.hadoop.io.SequenceFile;
 import org.apache.hadoop.io.Text;
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.LineIterator;

 //import Jama.Matrix.*;
 //import  java.io.IOException;
 import java.io.File;

 //import javax.sound.midi.SysexMessage;
 public class SequenceFileWriteDemo {
     public static void main(String[] args) throws IOException {
         String uri ="/home/hadoop/srcData/bDoubleArraySeq";
         Configuration conf = new Configuration();
         FileSystem fs = FileSystem.get(URI.create(uri), conf);
         Path path = new Path(uri);
         LongWritable key = new LongWritable();
         DoubleArrayWritable value = new DoubleArrayWritable();
         SequenceFile.Writer writer = null;
         try {
             writer = SequenceFile.createWriter(fs, conf, path, key.getClass(),
                     value.getClass());

             final LineIterator it2 = FileUtils.lineIterator(new File("/home/hadoop/srcData/transB.txt"), "UTF-8");
             try {
                 int i=0;
                 String[] strings;
                 DoubleWritable[] ArrayDoubleWritables;
                 while (it2.hasNext()) {
                     ++i;
                     final String line = it2.nextLine();
                     key.set(i);
                     strings=line.split("\t");
                     ArrayDoubleWritables=new DoubleWritable[strings.length];
                     for (int j = 0; j < ArrayDoubleWritables.length; j++) {
                         ArrayDoubleWritables[j] =new DoubleWritable(Double.valueOf(strings[j]));

                     }

                     value.set(ArrayDoubleWritables);
                     writer.append(key,value);
                     //System.out.println("ffd");

                 }
             } finally {
                 it2.close();
             }

         }finally {
             IOUtils.closeStream(writer);
         }
         System.out.println("ok");

     }

 }