Serialized object java

Question

Today I started using serialized object in java, I'm new at it and I have some problems when I try to deserialize. I have this file where I write all my Account objects, it writes fine I guess. The problem is I don't know how to refer to a specific object from that file, or how could I get all of them into a list? and then refer to it. This is how i'm trying to read them:

public void readAccount(Account e) {
/*  List<Account> results = new ArrayList<Account>();
    try {
        FileInputStream fileIn = new FileInputStream("test.txt");
        ObjectInputStream in = new ObjectInputStream(fileIn);
        for (int i = 0; i < accBank.size(); i++) {
            results.add((Account) in.readObject());
        }
        in.close();
        fileIn.close();
    } catch (IOException i) {
        i.printStackTrace();
        return;
    } catch (ClassNotFoundException c) {
        System.out.println("Employee class not found");
        c.printStackTrace();
        return;
    }
    for (Account acc : results) {
        System.out.println(toString(acc));
        if(e.getAcc_no() == acc.getAcc_no())
        {System.out.println("Deserialized Account...");
        System.out.println(toString(e));
        }
    }
    */
        List<Account> results = new ArrayList<Account>();
        Account acc = null;
        FileInputStream fis = null;
        try {
            fis = new FileInputStream("test.txt");
            while (true) {
                ObjectInputStream ois = new ObjectInputStream(fis);
                results.add((Account) ois.readObject());
                acc = (Account) ois.readObject();
            }
        } catch (Exception ignored) {
            // as expected
        } finally {
            if (fis != null)
                try {
                    fis.close();
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
        }
        System.out.println("results = " + results);

        for (Account ac : results) {
            System.out.println(toString(ac));
            if(e.getAcc_no() == ac.getAcc_no())
            {System.out.println("Deserialized Account...");
            System.out.println(toString(e));
            }
    }
}

And this is how I write them:

public void writeAccount(Account e) {
    try {
        ObjectOutputStream os1 = new ObjectOutputStream(
                new FileOutputStream("test.txt", true));
        os1.writeObject(e);
        os1.close();
    } catch (Exception exc) {
        exc.printStackTrace();
    }
}

Edit:

public void writeFile() {
    for (int i = 0; i < accBank.size(); i++) {
        writeAccount(retAcc(i));
    }
}

Can any of you tell me what im doing wrong? I also tried other examples from other questions and didn't work.

Answer 1

What you're doing wrong is that you use several ObjectOutputStreams to write to the same file (which is not a txt file, BTW, since it contains binary data), and use a single ObjectInputStream to read all the accounts. As a consequence, a new serialization header is written each time you write an account, and the ObjectInputStream doesn't expect that.

The best way to write a list of accounts is to do just that: you store the accounts into a List<Account>, and write the list. To read the list of accounts, you do just that: you read a single object from the file, and cast it to List<Account>.