Demonstrating Object Serialization

2006-04-11

Assuming you know the rules for Object Serialization, my aim in this article is to write an app in J# which does Object Serialization and then I shall decipher the serialized data.

Below is the app which does the object serialization. This app is inspired from :

https://www.visiblearea.com/visdoc/examples/Java/Thinking_in_Java/c12/documentation/Worm.html#Worm2

// Demonstrates Object Serialization

import java.io.*;

import java.util.*;

class Store implements Serializable {

private int n;

public Store(int n) { this.n = n; }

public String toString() { return Integer.toString(n); }

}

public class link implements Serializable {

private static int next_int = 0;

private Store[] d = {

new Store(next_int++),

new Store(next_int++)

};

private link next;

private char c;

// Value of i == number of segments

public link(int i, char x) {

c = x;

if(--i > 0)

next = new link(i, (char)(x + 1));

}

public link() {}

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

link w = new link(4, 'a');

ObjectOutputStream out = new ObjectOutputStream(

new FileOutputStream("link.out"));

out.writeObject(w);

out.close();

}

Now using the app from my previous post, when I try to read the contents of the output file link.out, I get the following result:

>file_bytes.exe link.out

ac ed 0 5 73 72 0 4 6c 69 6e 6b c8 f1 6d e 38 aa 2f ca 2 0 3 43 0 1 63 5b 0 1 64 74 0 8 5b 4c 53 74 6f 72 65 3b 4c 0 4 6e 65 78 74 74 0 6 4c 6c 69 6e 6b 3b 78 70 0 61 75 72 0 8 5b 4c 53 74 6f 72 65 3b 29 20 b6 39 0 37 55 a0 2 0 0 78 70 0 0 0 3 73 72 0 5 53 74 6f 72 65 ee f5 85 2f 82 b5 ab 5a 2 0 1 49 0 1 6e 78 70 0 0 0 0 73 71 0 7e 0 6 0 0 0 1 73 71 0 7e 0 6 0 0 0 2 73 71 0 7e 0 0 0 62 75 71 0 7e 0 4 0 0 0 3 73 71 0 7e 0 6 0 0 0 3 73 71 0 7e 0 6 0 0 0 4 73 71 0 7e 0 6 0 0 0 5 73 71 0 7e 0 0 0 63 75 71 0 7e 0 4 0 0 0 3 73 71 0 7e 0 6 0 0 0 6 73 71 0 7e 0 6 0 0 0 7 73 71 0 7e 0 6 0 0 0 8 73 71 0 7e 0 0 0 64 75 71 0 7e 0 4 0 0 0 3 73 71 0 7e 0 6 0 0 0 9 73 71 0 7e 0 6 0 0 0 a 73 71 0 7e 0 6 0 0 0 b 70

Total no of bytes read :286

Now, let us decipher this data. I would use “à” as a notation for “implies”

ac ed à STREAM MAGIC

0 5 à STREAM VERSION

73 à Terminal constant for OBJECT

72 à Terminal constant for CLASSDESC

0 4 à length of the class name (“link”)

6c 69 6e 6b à ‘l’ ‘i’ ‘n’ ‘k’

c8 f1 6d e 38 aa 2f ca à serialVersionUID

2 à serializable flag

0 3 à No of serializable fields in class “link”

43 à ‘C’ , primitive type code for Char

0 1 à length of the char field name i.e 1 here

63 à ‘c’ , name of the char field

5b à ‘[‘ , object type code for array

0 1 à length of the array field name i.e 1 here

64 à ‘d’ , name of the array field

74 à Terminal constant for STRING

0 8 à Length of type name is 8

5b 4c 53 74 6f 72 65 3b à ‘[‘ ‘L’ ‘S’ ‘t’ ‘o’ ‘r’ ‘e’ ‘;’ (field descriptor format)

4c à ‘L’ , object type code for object

0 4 à length of the object field name i.e 4 here

6e 65 78 74 à ‘n’ ‘e’ ‘x’ ‘t’

74 à Terminal constant for STRING

0 6 à Length of type name is 6

4c 6c 69 6e 6b 3b à ‘L’ ‘l’ ‘i’ ‘n’ ‘k’ ‘;’ (field descriptor format)

78 à Terminal constant for ENDBLOCKDATA

70 à Terminal constant for NULL (null reference for super class)

0 61 à char value is ‘a’

75 à Terminal constant for ARRAY

72 à Terminal constant for CLASSDESC

0 8 à Length of type name is 8

5b 4c 53 74 6f 72 65 3b à ‘[‘ ‘L’ ‘S’ ‘t’ ‘o’ ‘r’ ‘e’ ‘;’ (field descriptor format)

29 20 b6 39 0 37 55 a0 à serialVersionUID

2 à serializable flag

0 0 à No of serializable fields in the array class

78 à Terminal constant for ENDBLOCKDATA

70 à Terminal constant for NULL (null reference for super class)

0 0 0 3 à No of fields in the array

73 à Terminal constant for OBJECT

72 à Terminal constant for CLASSDESC

0 5 à String length of “Store”

53 74 6f 72 65 à ‘S’ ‘t’ ‘o’ ‘r’ ‘e’

ee f5 85 2f 82 b5 ab 5a à serialVersionUID

2 à serializable flag for Store class

0 1 à No of serializable fields in Store class

49 à ‘I’ , primitive type code for integer

0 1 à length of the char field name i.e 1 here

6e à ‘n’ , name of the char field in Store class

78 à Terminal constant for ENDBLOCKDATA

70 à Terminal constant for NULL (null reference for super class)

0 0 0 0 à int value of the field ‘n’ ( which is 0 here )

73 à Terminal constant for OBJECT