Exception StreamCorruptedException: invalid type code: AC

Question

I want to serialize a same object on file, each time when i run a program. This is a simple algorithm to explain my problem.

In the begening i store a String on writer. in the last i read a file. The goal of this program is if i run my program X time, i store and i print on screen X time my object.

class ReadFile {

    static ObjectOutputStream writer = null;

    public static void main(String[] args) throws IOException, ClassNotFoundException {

        writer = new ObjectOutputStream(new FileOutputStream("trace", true));
        store("String");

        if (writer != null) {
            writer.close();
        }

        open("file.tmp");

    }

    static public void store(String chaine) {
        if (writer == null) {
            return;
        }
        try {
            writer.writeObject(chaine);
        } catch (IOException ex) {
        }
    }

    static public void open(String file) throws FileNotFoundException, IOException, ClassNotFoundException {
        StringBuilder str = new StringBuilder();
        ObjectInputStream objs;
        try {

            objs = new ObjectInputStream(new FileInputStream(file));
            try {
                while (true) {
                    Object obj = objs.readObject();
                    str.append(obj.toString());
                }
            } catch (EOFException ex) {
            }
            objs.close();

        } catch (Exception ex) {
            ex.printStackTrace(System.err);
        }
    }
}

When i run this program i have this error :

java.io.StreamCorruptedException: invalid type code: AC
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1355)
        at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
        at ReadFile.open(ReadFile.java:47)
        at ReadFile.main(ReadFile.java:35)

What can i do please ?

Answer 1

According to this post you cannot append to a ObjectOutputStream, which you are trying to do by opening the underlying FileOutputStream in append mode. There is a solution mentioned on that post such that you create an AppendableObjectOutputStream , or you could just open the FileOutputStream without appending.