write mutiple object states of serilizable object.

[akb]

can i write multiple object states of a serializable in a single file?
if i can then how can i read back those states?

i have no problem with writing multiple object states in a file.
but i can't read back the all object states what i saved so far.

only after reading back the first state then StreamCorruptedException exception thrown.

i know it is due to data inconsistency in the file.

so plz help me.
Regards.

[r035198x]

can i write multiple object states of a serializable in a single file?
if i can then how can i read back those states?

i have no problem with writing multiple object states in a file.
but i can't read back the all object states what i saved so far.

only after reading back the first state then StreamCorruptedException exception thrown.

i know it is due to data inconsistency in the file.

so plz help me.
Regards.

Can we see the codes.

[JosAH]

can i write multiple object states of a serializable in a single file?
if i can then how can i read back those states?

i have no problem with writing multiple object states in a file.
but i can't read back the all object states what i saved so far.

only after reading back the first state then StreamCorruptedException exception thrown.

i know it is due to data inconsistency in the file.

so plz help me.
Regards.

Unless you reset the ObjectOutputStream or writeUnshared() every object is
written to such a stream only once. Every following attempt to write the object
only a reference to a previously serialized incarnation is written to the stream.

kind regards,

Jos

[dmjpro]

actually this Q. is sent by me on behalf of AKB. so i send u the source code.

as per as ro35198x requirements concern ...

my code is something like this .....

//this is my SERIALIZABLE class which is to be serialized.

class s implements Serailizable
{
private int a ,b;
public s(int A,int B){a=A;b=B;}
public void display(){
System.out.println("DMJ: " + a + "\t" + b);
}
}

//this is my main class

class m
{
public static void main(String args[])
{
FileOutputStream o = new FileOutputStream(file_name,true);
//the file opened in append mode
ObjectOutputStream out = new ObjectOutputStream(o);
out.writeObject(new s(100,200));
out.writeObject(new s(300,400));

FileInputStream i = new FileInputStream(file_name);
ObjectInputStream in = new ObjectInputStream(i);
((s)in.readObject()).display(); //this is OK ... it shows the first state i saved.
((s)in.readObject()).display();
//the second call is throwing StreamCorruptedException.
}
}

plz help.
kind regards.

[JosAH]

An ObjectOutputStream writes header information to the wrapped stream when
you open/create it. Your file contains the following information:

HHHOOOOO ... OOO

where HHH represents the header information and OOO ... OOO represents
the data for the serialized object itself. When you reopen your file in append
mode again and open an ObjectOutputStream again, the header will also be
written again. After writing another object the file contents look like this:

HHHOOOOO ... OOOHHHOOOOO ... OOO

When you want to read objects from this file you can read the first one but
unexpectedly another header is read when you want to read the second object.

kind regards,

Jos

[akb]

now the full clearity comes up....
thanx for ur reply...

then what is the solution ... to accomplish this.

Plz help.
Kind regards.

[JosAH]

now the full clearity comes up....
thanx for ur reply...

then what is the solution ... to accomplish this.

Plz help.
Kind regards.

Open the ObjectOutputStream once and write all your objects. At the end
close the stream. You can read all your objects later by opening the file,
wrap it in an ObjectInputStream and read all the objects.

That way the header will only be written once.

kind regards,

Jos

[dmjpro]

ok we got the solution ....

lot of thanxxxx .....

[dmjpro]

@JosAH
What did you mean here ? will you please say in details ?

[JosAH]

@dmjpro
Exactly as I wrote: if you do e.g. something like this:

BigObject bo= new BigObject();
ObjectOutputStream oos= ...;
 
oos.write(bo);
bo.changeState();
oos.write(bo);
bo.changeState();
oos.write(bo);
oos.close();
 

The content of that oos will be:

<header><BigObject content><ref><ref>

Where the <header> part is important to an ObjectInputStream only, <BigObject content> is the content of your object before the two changeState() calls and the <ref> parts are references to that first BigObject content.

kind regards,

Jos

[dmjpro]

@JosAH

Wow it saves the memory... cool ;)
One thing tell me what's the role of clone in serialization?

[JosAH]

@dmjpro
None; the clone() method isn't used by the serialization framework. It has to save memory as you call it because of circular references: if an object A (which must be Serializable) refers to an object B ( which also has to be Serializable) is serialized both objects A and B are serialized. Now assume object B also refers to object A; you don't want an infinite sequence of serialized objects A, B, A, B, A, B etc. You want a sequence like: <objectA content><object B content><ref to first object A>.

kind regards,

Jos