How to appends objects in byte stream using ObjectOutputStream

Question

I want to append multiple object at the end to the same binary file using ObjectOutputStream
But when I run the following code more than one time I get the exception

java.io.StreamCorruptedException: invalid type code: AC

The question is
Is there any headers things that I should know to APPEND OBJECTS at the end of the file in java?

package sourcepackage;

import sourcepackage.persons.Person;
import sourcepackage.persons.Student;

import java.io.*;

public class MainClass {
    public static void main(String[] args) {

        Person mahmoud_kanbar = new Student(21, 224466, "Mahmoud Kanbar", "ITE");


        try {

            FileOutputStream out = new FileOutputStream("Hello.dat", true);

            ObjectOutputStream objectOut = new ObjectOutputStream(out);

            objectOut.writeObject(mahmoud_kanbar);

            objectOut.close();
            out.close();

            FileInputStream in = new FileInputStream("Hello.dat");

            ObjectInputStream objectIn = new ObjectInputStream(in);


            while (in.available() != 0) {
                Person hi = (Person) objectIn.readObject();
                hi.printInfo();
            }

            objectIn.close();
            in.close();

        } catch (Exception e) {

            System.out.println(e);

        }


    }
}

I was searching for decades about a solution to this problem and I couldn't find anything
I want to append objects just like the c++ do

The answer to my question is in a previous post [link](https://stackoverflow.com/a/1195078/10461503) — Mahmoud Kanbar, Oct 03 '20 at 01:26

Omid.N · Answer 1 · 2020-10-02T06:53:05.527

You can append objects to the same ObjectOutputStream with writeObject() method. When reading, they are read in the same order they were written. Also, you may be getting that error because your stream is buffered and not written. You should use flush() method to make sure the buffer has been written to the file.
Let's write two objects to the same file and read them:

Person mahmoud_kanbar = new Student(21, 224466, "Mahmoud Kanbar", "ITE");
Person omid = new Student(18, 200000, "Omid Nejadabbasi", "ITE");

try {

        FileOutputStream out = new FileOutputStream("Hello.dat", true);
        ObjectOutputStream objectOut = new ObjectOutputStream(out);
        objectOut.writeObject(mahmoud_kanbar);
        objectOut.writeObject(omid);
        objectOut.flush();
        objectOut.close();
        out.close();

        FileInputStream in = new FileInputStream("Hello.dat");

        ObjectInputStream objectIn = new ObjectInputStream(in);


        Person newPerson= (Person)  objectIn.readObject();
        newPerson.printInfo();
        newPerson= (Person)  objectIn.readObject();
        newPerson.printInfo();

        objectIn.close();
        in.close();

    } catch (Exception e) {

        System.out.println(e);

    }

readObject() deserializes the next Object serialized into the stream.

That doesn't work, I want to append the next time I open the program — Mahmoud Kanbar, Oct 02 '20 at 22:13

How to appends objects in byte stream using ObjectOutputStream

1 Answers1