Hadoop源码分析3: 序列化

1. Java 默认序列化

public class Block1 implements Serializable {

    private static finallong serialVersionUID = 1276464248616673062L;

    privatelong blockId;

    privatelong numBytes;

    privatelong generationStamp; 

    publicBlock1() { 

    }

    publicBlock1(final long blkid, final long len, final longgenerationStamp) {

      this.blockId = blkid;

      this.numBytes = len;

      this.generationStamp =genStamp;

   } 

    @Override

    publicString toString() {

      return "Block1 [blockId=" +blockId + ", numBytes=" + numBytes

          +", generationStamp=" + generationStamp + "]";

   } 

      // setter getter...............

}

2.Hadoop 序列化

public class Block2 implements Writable { 

       static { // register a ctor

   WritableFactories.setFactory(Block2.class,new WritableFactory() {

      public Writable newInstance(){

          return new Block2();

      }

      });

    }

    privatelong blockId;

    privatelong numBytes;

    privatelong generationStamp;

    publicBlock2() { 

    }

    publicBlock2(final long blkid, final long len, final longgenerationStamp) {

      this.blockId = blkid;

      this.numBytes = len;

      this.generationStamp =genStamp;

    }

 

    publicvoid set(long blkid, long len, long genStamp) {

      this.blockId = blkid;

      this.numBytes = len;

      this.generationStamp =genStamp;

   } 

 

   @Override

   publicvoid write(DataOutput out) throws IOException {

      out.writeLong(blockId);

      out.writeLong(numBytes);

      out.writeLong(generationStamp);

   }

   @Override

   publicvoid readFields(DataInput in) throws IOException{

      this.blockId = in.readLong();

      this.numBytes =in.readLong();

      this.generationStamp =in.readLong();

      if (numBytes < 0) {

          throw new IOException("Unexpected blocksize: " + numBytes);

      }

   } 

       // settergetter...............

  @Override

    publicString toString() {

      return "Block2 [blockId=" +blockId + ", numBytes=" + numBytes

         + ", generationStamp=" +generationStamp + "]";

   } 

}

2. 比较 

public class BlockMain {

    publicstatic void main(String[] args) throws IOException {

      Block1 block1 = newBlock1(7806259420524417791L, 39447755L, 56736651L);

       ByteArrayOutputStream out1 = newByteArrayOutputStream();

       ObjectOutputStream objOut1 = newObjectOutputStream(out1);

       objOut1.writeObject(block1);

       objOut1.close();

       System.out.println("writeObject (block1) with "+ out1.size() + " bytes:");

       SerializationExample.print16(out1.toByteArray(),out1.size());

       System.out.println();

       Block2 block2 = new Block2(7806259420524417791L,39447755L, 56736651L);

       ByteArrayOutputStream out2 = newByteArrayOutputStream();

       ObjectOutputStream objOut2 = newObjectOutputStream(out2);

       block2.write(objOut2);

       objOut2.close();

       System.out.println("writeObject (block2) with "+ out2.size() + " bytes:");

       SerializationExample.print16(out2.toByteArray(),out2.size());

    }

}

打印：

writeObject (block1) with 113 bytes:

AC ED 00 05 73 72 00 1D  6F 72 67 2E 68 61 646F    ....sr.. org.hado

6F 70 69 6E 74 65 72 6E  61 6C 2E 73 65 72 2E42    opintern al.ser.B

6C 6F 63 6B 31 11 B6 E9  78 9B 48 5F 26 02 0003    lock1... x.H_&...

4A 00 07 62 6C 6F 63 6B  49 64 4A 00 0F 67 656E    J..block IdJ..gen

65 72 61 74 69 6F 6E 53  74 61 6D 70 4A 00 086E    erationS tampJ..n

75 6D 42 79 74 65 73 78  70 6C 55 67 95 68 E792    umBytesx plUg.h..

FF 00 00 00 00 03 61 BB  8B 00 00 00 00 02 59EC    ......a. ......Y.

CB                                          .

writeObject (block2) with 30 bytes:

AC ED 00 05 77 18 6C 55  67 95 68 E7 92 FF 0000    ....w.lU g.h.....

00 00 02 59 EC CB 00 00  00 00 03 61 BB 8B        ...Y.... ...a..

可见使用Writable的数据量比Serializable 小得多: 30/113 约为 26.6%。

3.文件读写对象

public class BlockMain {

public static void main(String[] args) throwsIOException, ClassNotFoundException {

    Filefile =new File("d:\\1.txt");

   FileOutputStream fos = newFileOutputStream(file);

   ObjectOutputStream objOut = newObjectOutputStream(fos);

   FileInputStream fis = newFileInputStream(file);

   ObjectInputStream objIn = newObjectInputStream(fis);

    Block1block1 = new Block1(7806259420524417791L, 39447755L,56736651L);

   objOut.writeObject(block1);

   objOut.close();

   Block1 block1Retrive =(Block1) objIn.readObject();

   System.out.println("writeObject(block1) : " + block1Retrive + " ");

   objIn.close();

   System.out.println();

   

    file=new File("d:\\2.txt");

    fos =new FileOutputStream(file);

    objOut= new ObjectOutputStream(fos);

    fis =new FileInputStream(file);

    objIn =new ObjectInputStream(fis);

    Block2block2 = new Block2(7806259420524417791L, 39447755L,56736651L);

   block2.write(objOut);

   objOut.close();

   Block2 block2Retrive = newBlock2();

   block2Retrive.readFields(objIn);

   objIn.close();

   System.out.println("writeObject(block2) : " + block2Retrive + " ");

 

}

}

打印：

writeObject (block1) : Block1 [blockId=7806259420524417791,numBytes=39447755,generationStamp=56736651] 

writeObject (block2) : Block2 [blockId=7806259420524417791,numBytes=39447755,generationStamp=56736651] 

文件内容：

d:\1.txt 113 字节

d:\2.txt 30 字节