IOException in ObjectInputStream in java

Question

I have problem with my code. I get IOException when I use readObject in my code. the whole program work correctly but when I want to use readObject I get this exception, this is the code I use for saving object:

        File f = new File("employees.obj");
    ObjectOutputStream objOut = null;

    try {

        objOut = new ObjectOutputStream(new BufferedOutputStream(
                new FileOutputStream(f)));
        objOut.writeObject(newEmployee);
        objOut.flush();

        System.out.println("Object is serialized.");

    } catch (FileNotFoundException e) {
        System.out.println("File not found!");

    } catch (IOException e) {
        System.out.println("Failed!");

    } finally {

        if (objOut != null) {
            try {

                objOut.close();
            } catch (IOException e) {
            }
        }
    }

and it is the code I use for restoring object:

    File f = new File("employees.obj");
    ObjectInputStream objIn = null;
    ArrayList<Employee> c = new ArrayList<Employee>();
    try {
        objIn = new ObjectInputStream(new BufferedInputStream(
                new FileInputStream(f)));
        while (objIn.readObject() != null) {
            Person employee = (Person) objIn.readObject();
            System.out.println("hello");
            System.out.println(employee.toString());
        }
        System.out.println(c.toString());
        return c;

    } catch (FileNotFoundException e) {
        System.out.println("1");
    } catch (IOException e) {
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        System.out.println("3");
    } catch (ClassCastException e) {
        System.out.println("4");
    } finally {

        if (objIn != null) {
            try {
                objIn.close();
            } catch (IOException e) {
                System.out.println("4");
            }
        }
    }
    return c;

and the result in console:

at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2553)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1296)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:350)
at org.bihe.DeSerializer.deSerializeEmployees(DeSerializer.java:20)
at org.bihe.Main.enterAsManager(Main.java:238)
at org.bihe.Main.menu(Main.java:92)
at org.bihe.Main.main(Main.java:50)

Answer 1

You already read the object in the while loop test.

    while (objIn.readObject() != null) {
        Person employee = (Person) objIn.readObject();
        System.out.println("hello");
        System.out.println(employee.toString());
    }

Change it to:

    for (Person employee = (Person) objIn.readObject(); employee != null; Person employee = (Person) objIn.readObject()) {
        System.out.println("hello");
        System.out.println(employee.toString());
    }

Answer 2

In addition to the underlying problem of reading twice, you have another problem. EOFException just means you've reached the end of the stream. Catch it, and break out of the loop. At present your code incorrectly assumes that readObject() returns null at end of stream. It doesn't. It returns null if you wrote a null, which can happen any time, or never, depending entirely in what you wrote to the stream.

Answer 3

    while (objIn.readObject() != null) {

will deseralize one object (Person). Then the next line:

        Person employee = (Person) objIn.readObject();

attempts to deseralize the next object. If you're at the end of the file (EOF), then it throws IOException.

To fix this do something like this:

    Person employee;
    while ((employee = (Person)objIn.readObject()) != null) {
        System.out.println("hello");
        System.out.println(employee.toString());
    }

The while compares readObject() with null and assigns it to employee.