Question

I have saved an arrayList into a binary file by using serialastion. How do I now retrieve this data from the binary file?

This is the code I have used for serialisation

public void createSerialisable() throws IOException
{
    FileOutputStream fileOut =  new FileOutputStream("theBkup.ser");
    ObjectOutputStream out =  new ObjectOutputStream(fileOut);
    out.writeObject(allDeps);
    options();
}

and this the code I am trying to use for deserialization of the arrayList:

public void readInSerialisable() throws IOException
{
    FileInputStream fileIn = new FileInputStream("theBKup.ser");

    ObjectInputStream in = new ObjectInputStream(fileIn);

    try
    {
     ArrayList readob  = (ArrayList)oi.readObject();  
               allDeps = (ArrayList) in.readObject();
    }
    catch (IOException exc)
    {
        System.out.println("didnt work");
    }
}

allDeps is the declared array list in the classes constructer. Im trying to save the arrayList from the file to the arrayList declared in this class.

Answer 1

Your code is mostly correct, but there is one mistake and a couple of things that might make it work better. I’ve highlighted them with asterisks (since, apparently, I can’t make them bold in ‘code’ mode).

public void createSerialisable() throws IOException
{
    FileOutputStream fileOut =  new FileOutputStream("theBkup.ser");
    ObjectOutputStream out =  new ObjectOutputStream(fileOut);
    out.writeObject(allDeps);
    **out.flush();** // Probably not strictly necessary, but a good idea nonetheless
    **out.close();** // Probably not strictly necessary, but a good idea nonetheless
    options();
}

public void readInSerialisable() throws IOException
{
    FileInputStream fileIn = new FileInputStream("theBKup.ser");

    ObjectInputStream in = new ObjectInputStream(fileIn);

    try
    { 
        **// You only wrote one object, so only try to read one object back.**
        allDeps = (ArrayList) in.readObject();
    }
    catch (IOException exc)
    {
        System.out.println("didnt work");
        **exc.printStackTrace();** // Very useful for findout out exactly what went wrong.
    }
}

Hope that helps. If you still see a problem then make sure you post the stack trace and a complete, self-contained, compilable example that demonstrates the problem.

Note that I’ve assumed that allDeps contains objects that are actually Serializable and that your problem is in readInSerialisable rather than in createSerialisable. Again, a stack trace would be extremely helpful.