Reputation: 623

Java Serialization

I'm learning now how to do serialization using Java Language. I have read some posts and docs about the subject and I tried to do a simple example (below)

public class SterializeObject implements java.io.Serializable{

        /**
         * 
         */
        private static final long serialVersionUID = 1L;

        private String name;
        private transient int code;

        public SterializeObject (String n, int c){
            name = n;
            code = c;
        }

        public void printAtributes (){
            System.out.println("name: " + name + "; code: " + code);
        }
    }

    public class MainClass {
        public static void main(String[] agrs) {
            SterializeObject ob1 = new SterializeObject("ana", 1);
            SterializeObject ob2 = new SterializeObject("rita", 2);

            try {
                FileOutputStream fileOut = new FileOutputStream("file.data");
                ObjectOutputStream outObj = new ObjectOutputStream(fileOut);
                outObj.writeObject(ob1);
                outObj.writeObject(ob2);
                outObj.close();
                System.out.println("Objects were serialized!");
            } catch (IOException e) {
                e.printStackTrace();
            }

            ArrayList<SterializeObject> list = new ArrayList<SterializeObject>();
            try {
                FileInputStream fileInput = new FileInputStream("file.data");
                ObjectInputStream inputObj = new ObjectInputStream(fileInput);
                Object o;
                try {
                    while ((o = inputObj.readObject()) != null) {
                        list.add((SterializeObject) o);
                    }
                } catch (ClassNotFoundException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    System.out.println("Erro foi aqui! (1)");
                }

                inputObj.close();
                fileInput.close();
            } catch (IOException e) {
                e.printStackTrace();
                System.out.println("Erro foi aqui! (2)");
            }

            for (int i = 0; i < list.size(); ++i) {
                list.get(i).printAtributes();
            }
        }
    }

I created a Class SterializeObject that implements java.io.Serializable with two variables: one string (name) and one int (code) that is transient. Then In the main I generate two instances of that class and I tried to write it in a file, that I have done successfully! After that, I try to read the two object with a Loop.. there is my problem.. since the ObjectInputStream dosen't have some kind of method to see if we are in the end or not. So, I tried to do with this condition: (o = inputObj.readObject()) != null.

My output is this:
java.io.EOFException
    at java.io.ObjectInputStream$BlockDataInputStream.peekByte(Unknown Source)
    at java.io.ObjectInputStream.readObject0(Unknown Source)
    at java.io.ObjectInputStream.readObject(Unknown Source)
    at MainClass.main(MainClass.java:30)
Objects were serialized!
Erro foi aqui! (2)
name: ana; code: 0
name: rita; code: 0

I get the objects, but I get an error because, I think, is trying to access to something that doesn't exist.

Someone can tell me other way to do it?

Best Regards.

Upvotes: 2

Answers (6)

aboliveira

Reputation: 623

As many of you told me to do, I created a ArrayList and serialized the ArrayList. My code is:

public class MainClass {
    public static void main(String[] agrs) {
        SterializeObject ob1 = new SterializeObject("ana", 1);
        SterializeObject ob2 = new SterializeObject("rita", 2);

        ArrayList <SterializeObject> list = new ArrayList<>();
        list.add(ob1);
        list.add(ob2);

        ArrayList <SterializeObject> input = new ArrayList<SterializeObject>();

        try {
            FileOutputStream fileOut = new FileOutputStream("file.data");
            ObjectOutputStream outObj = new ObjectOutputStream(fileOut);
            outObj.writeObject(list);
            outObj.close();
            System.out.println("Objects were serialized!");
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            FileInputStream fileInput = new FileInputStream("file.data");
            ObjectInputStream inputObj = new ObjectInputStream(fileInput);
            Object o;
            try {
                input = (ArrayList<SterializeObject>) inputObj.readObject();

            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                System.out.println("Erro foi aqui! (1)");
            }

            inputObj.close();
            fileInput.close();
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("Erro foi aqui! (2)");
        }

        for (int i = 0; i < input.size(); ++i) {
            input.get(i).printAtributes();
        }
    }
}

And the output is: Objects were serialized! name: ana; code: 0 name: rita; code: 0

Thank you for the help!

Upvotes: 2

Anand Padigala

Reputation: 1

Replace your while loop with this piece of code

do{
        try
        {
            o = inputObj.readObject();
            list.add((SterializeObject) o);
        }
        catch(EOFException e)
        {
            o = null;
        }
}while (o != null);

Upvotes: 0

Mppl

Reputation: 961

You can do this by placing the readObject call inside a try-catch block and catching that EOFException you get, signaling you have read all the objects.

Upvotes: 0

Sergio Pinto

Reputation: 76

Why don't you add both object to an ArrayList, and serialize the ArrayList. Then you just have to Deserialize the ArrayList and it will be populated with both objects.

Upvotes: 0