Cannot append data to a file

[Jas Oberai]

Hi Friends,
I have 4 java classes:

Main class   :mrgreen:   isplays menu
Add class : Adds a new record to the file
Here to open the file i use this:
oos = new ObjectOutputStream(new FileOutputStream( "file.ser") );
 
Print class : Prints the record in the file
ois = new ObjectInputStream(new FileInputStream( "file.ser" ) );
 
 
Bean : Defines the Record.

But for some reasons only the last record entered is printed.I also tried to append data to the file,like this:

oos = new ObjectOutputStream(new FileOutputStream( "file.ser",true));

but then it starts giving me some error.can someone please tell me whats wrong,and how can i see the total records entered into the file.

And my second question is what is a blocked/fielded data file??

Please answer my question friends.
Thanks

[ October 10, 2005: Message edited by: jas oberai ]
[ October 10, 2005: Message edited by: jas oberai ]

[Joe Ess]

Opening the same file for writing twice is a Bad Idea, especially with ObjectOutputStream. OOS writes a header as soon as it opens, so it's probably overwriting existing data. You can't append objects to a file of serialized objects (again, the header). If you want to write multiple objects using OOS, I suggest you put the objects into a collection (i.e. an ArrayList) and serialize that.

[Jas Oberai]

hi joe,
i have coded everything and ow i wont like to r-write it again using Collections.I have exactly the same problem that you discussed with this person over here:
https://coderanch.com/t/277067/Streams/java/Appending-file-containing-serialized-Objects

Can you please elaborate on what you said..and tell me how can i accomplish this.
Also,the same was discussed here,but very hard to understand:
http://forum.java.sun.com/thread.jspa?threadID=581792&tstart=0

I just want to store student records in a file,and read them..so do i need to have this serialization feature??Or I can get rid of it and make my life easier.
Thanks
[ October 10, 2005: Message edited by: jas oberai ]

[Joe Ess]

I was quoting from the serialization faq in that topic. I've never done it, so I can't give you much more insight.
If you want alternatives, it really depends on what your requirements are. If you just want to write data out, plain text files may work. If you want to be able to load one record at a time in random order, RandomAccessFile may be your answer.

[Jas Oberai]

Thanks Joe,
I am using Vectors now as you said.I am able to write data but when I try to read it gives me this error:

java.io.StreamCorruptedException
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1326)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:339)

This is my code to read the data:

      do{
 this.o = input.readObject();
 if(this.o != null)
         vector.addElement(( AccountRecordSerializable ) this.o);
         }while(this.o != null);
   
 AccountRecord record;
for ( int counter = 0; counter < vector.size(); counter++ )
{
record = (AccountRecord)vector.elementAt(counter);
System.out.printf( "%-11s %-11s %-13s %-7d \n",
         record.getName(), record.getSurName(),record.getPhoneNo(), record.getAge() );
}

If I uncomment the do-while loop,everything goes fine and it displays one record.But I want to display all the records.Can someone please tell me how to solve this error ,I will be very much thankful to you.
Thanks

[Joe Ess]

Sounds like you are corrupting the stream. What does your write code look like? Are you still opening the output stream twice? Still trying to append to the output stream?

[Ilja Preuss]

Moving to our IO forum...

[Carla carmona]

What about using RandomAccessFile ? Get the end of the file using: long pointer = raf.getFilePointer() and point to this location using raf.seek(pointer) as the place to start writing to.


Jose Cardoso
SCJP