reading objects from file

Question

I have a problem with reading objects from file Java.

file is an arraylist<projet>

This is the code of saving objects :

try {
    FileOutputStream fileOut = new FileOutputStream("les projets.txt", true);
    ObjectOutputStream out = new ObjectOutputStream(fileOut);

    for (projet a : file) {
        out.writeObject(a);
    }
    out.close();
} catch (Exception e) {
    e.printStackTrace();
}

And this is the code of reading objects from file ::

try {
    FileInputStream fileIn = new FileInputStream("les projets.txt");
    ObjectInputStream in = new ObjectInputStream(fileIn);

    while (in.available() > 0){
        projet c = (projet) in.readObject();

        b.add(c);
    }

    choisir = new JList(b.toArray());
    in.close();
} catch (Exception e) {
    e.printStackTrace();
}

Writing is working properly. The problem is the reading... it does not read any object (projet) What could be the problem?

Answer 1

As mentioned by EJP in comment and this SO post . if you are planning to write multiple objects in a single file you should write custom ObjectOutputStream , because the while writing second or nth object header information the file will get corrupt.
As suggested by EJP write as ArrayList , since ArrayList is already Serializable you should not have issue. as

out.writeObject(file) and read it back as ArrayList b = (ArrayList) in.readObject();
for some reason if you cant write it as ArrayList. create custome ObjectOutStream as

class MyObjectOutputStream extends ObjectOutputStream {

public MyObjectOutputStream(OutputStream os) throws IOException {
    super(os);
}

@Override
protected void writeStreamHeader() {}

}

and change your writeObject as

try {
        FileOutputStream fileOut= new FileOutputStream("les_projets.txt",true);
        MyObjectOutputStream out = new MyObjectOutputStream(fileOut );

         for (projet a : file) {
    out.writeObject(a);
}
        out.close();
    }

    catch(Exception e)
    {e.printStackTrace();

}

and change your readObject as

ObjectInputStream in = null;
    try {
        FileInputStream fileIn = new FileInputStream("C:\\temp\\les_projets1.txt");
        in = new ObjectInputStream(fileIn );

        while(true) {
            try{
                projet c = (projet) in.readObject();
                b.add(c);
            }catch(EOFException ex){
                // end of file case
                break;
            }

        }

    }catch (Exception ex){
        ex.printStackTrace();
    }finally{
        try {
            in.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }