1.java.lang.Object
  |__ java.io.OutputStream
           |__ java.io.ByteArrayOutputStream
                  //description
                     public class ByteArrayOutputStream
                     extends OutputStream
                   //method
                     byte[] toByteArray()   //Creates a newly allocated byte array.
2.java.lang.Object
      |__ java.io.OutputStream
               |__ java.io.FilterOutputStream
                        |__ java.io.DataOutputStream
                             //description
                                public class DataOutputStream
                                extends FilterOutputStream
                                implements DataOutput
3. java.lang.Object
      |__ java.io.OutputStream
           // description
               public abstract class OutputStream
               extends Object
                implements Closeable, Flushable
            //mdthods
               void close()
               void flush()
               void write(byte[] b)
               void write(byte[] b, int off, int len)
               abstract void write(int b)
4.org.apache.hadoop.io
Interface Writable
 //description
    public interface Writable
 //methods
   void readFields(DataInput in)
   void write(DataOutput out)
5. java.lang.Object
       |__ org.apache.hadoop.io.IntWritable
              //description
                 public class IntWritableextends Object
                 implements   WritableComparable
               // methods
                   int get()
                   void readFields(DataInput in)
                   void set(int value)
                   void write(DataOutput out)
6. java.lang.Object
      |__ org.apache.hadoop.util.StringUtils
            //description
              public class StringUtils
              extends Object
            //method
               static String byteToHexString(byte[] bytes)
               static String capitalize(String s)
               static String[] split(String str)
               static Path[] stringToPath(String[] str)
               static URI[] stringToURI(String[] str)
               static String uriToString(URI[] uris) 

import java.io.DataOutputStream;
import java.io.ByteArrayOutputStream;
import java.lang.Byte;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.StringUtils;
public class TestWritable extends IntWritable {

  public static byte[] serialize(IntWritable writable) throws Exception {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    DataOutputStream dataOut = new DataOutputStream(out);
    writable.write(dataOut);
    dataOut.close();
    return out.toByteArray();
  }

  public static void main(String[] args) throws Exception {
    IntWritable i = new IntWritable();
    i.set(8);
    System.out.println(i.get());
    byte[] bytes = serialize(i);
    System.out.println(bytes.toString().length());
    System.out.println(StringUtils.byteToHexString(bytes));
  }
}