How to append to an ObjectInputStream without getting java.io.StreamCorruptedException: invalid type code: AC? [duplicate]

Question

I am trying to read some objects from a file. The code works fine for the first iteration and at the second iteration it gives a StreamCorruptedException. Here is my code,

private ArrayList<Cheque> cheques = null;
ObjectInputStream ois = null;
        try {
            cheques = new ArrayList<Cheque>(4);
            ois = new ObjectInputStream(new FileInputStream("src\\easycheque\\data\\Templates.dat"));
            Object o = null;
            try {
                o = ois.readObject();
                int i=1;
                while (o != null) {
                    cheques.add((Cheque) o);
                    System.out.println(i++); // prints the number of the iteration
                    o = ois.readObject(); // exception occurs here
                }
            } catch (ClassNotFoundException ex) {// for ois readObject()
                Logger.getLogger(TemplateReader.class.getName()).log(Level.SEVERE, null, ex);

            } catch (EOFException ex) {// for ois readObject()
                // end of the file reached stop reading
                System.out.println("ois closed");
                ois.close();

            }
        } catch (IOException ex) {
            Logger.getLogger(TemplateReader.class.getName()).log(Level.SEVERE, null, ex);
        }

below is part of the exception. Before printing this '1' is printed (because of the sout)

SEVERE: null
java.io.StreamCorruptedException: invalid type code: AC
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1356)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351) 

I can't figure out why this is happening. In few forum posts, I came across that this happens when you append to a file during writing it. Is it the real reason?. (I am appending to the file during writing phase). If so is there a proper way to read an appended file?

here is the code i use to write to the file

 ObjectOutputStream objectOut = new ObjectOutputStream(new FileOutputStream("src\\easycheque\\data\\templates.dat", true));

 objectOut.writeObject(cheque);
 objectOut.flush();
 objectOut.close();

writing is not an iterative process.

Thank you :)

Answer 1

(I am appending to the file during the writing phase)

And that is the problem. You can't append to an ObjectOutputStream. That will definitly corrupt the stream and you get StreamCorruptedException.

But I already left a solution to this problem on SO: an AppendableObjectOutputStream

EDIT

From the writer I see that you write one cheque object and flush and close the stream. From the reader, I clearly see, that you're trying to read more than one cheque object. And you can read the first one but not the rest. So to me it is perfectly clear, that you reopen the Stream and append more and more cheque objects. Which is not allowed.

You have to write all cheque objects in 'one session'. Or use the AppendableObjectOutputStream instead of the standard ObjectOutputStream.

Answer 2

Creating a new ObjectInputStream without closing the underlying FileInputStream solves this problem:

    FileInputStream fin = new FileInputStream(file);
    while (...) {
        ObjectInputStream oin = new ObjectInputStream(fin);
        Object o = oin.readObject();
        ...
    }
    fin.close();