Serialized Object size?

Question

I am writing an object to a file. The object is basically a data chunk from a file, with some other information added. The thing I don't understand is that the input file is around 10 KB, but the output file is about 20 KB, but data I add one only a few bytes.

What could be the reason? Are there some object identifiers, attributes also logged and occupy some space apart from the data chunk.

Code Snippet:

public void writePacket(Packet packet) {
  String fileName = packet.getName();
  String filePath = dtnStore+fileName ;
  ObjectOutputStream out = null;
  File file = new File(filePath);
  if(!file.exists())
    out =  new ObjectOutputStream(new FileOutputStream   (filePath));
  else
    out = new AppendableObjectOutputStream (new FileOutputStream (filePath, true));
  out.writeObject(packet);
  out.flush ();
}

how are you writing the data to that file? what properties does your "object" have? — Mat
– Mat, Commented Jun 11, 2011 at 7:29
@quamar, I took the liberty of editing your question so that it makes more sense to a native English speaker. I hope that's what you intended to ask, but clearer? If not then please feel free to edit your question... and even change it back. — corlettk
– corlettk, Commented Jun 11, 2011 at 7:32
We'll need to see samples of both the input and output files in order to make any educated guesses as to where the bloat arises. If you where, say, reading tab-delimited files, and writing XML then you'd have your explanation. — corlettk
– corlettk, Commented Jun 11, 2011 at 7:34
@corlettk: I prefer to try and get people to learn instead of doing the translation for them. Give that a shot next time and see if they can actually produce correct English. Still, good work, for the question does actually read better due to the edits. — Robert Massaioli
– Robert Massaioli, Commented Jun 11, 2011 at 7:38
Show some code please - ideally a short but complete program demonstrating the problem. There's not enough information here to answer you. — Jon Skeet
– Jon Skeet, Commented Jun 11, 2011 at 7:38

Peter Lawrey · Accepted Answer · 2011-06-11 07:59:00Z

2

ObjectOutputStream is a reasonable verbose format. It includes a lot of information about how to reconstruct an object including its types. Most file formats don't contain this information which makes them smaller but not as convenient for a Java developer to use.

Unless your input is from an ObjectInputStream the file size can take dramatically.

e.g. say you read an Integer from a text file say 100\n is 4 bytes, but when you writ this to a ObjectOutputSTream it will be 81 bytes long as it include a header, the type of the object, Number the field names etc.

answered Jun 11, 2011 at 7:59

Peter Lawrey

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