Qestion about convert Object to byte[] and convert it back

I need to convert an object to String to store it into structure in our
application, so I write some function to convert Object into byte[] and
convert it back. The following is a test program:

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class test {
    private static Object getObjectFromByteArr(byte [] byteArr) throws
java.io.IOException, ClassNotFoundException {
        ObjectInputStream in = new ObjectInputStream(new
ByteArrayInputStream(byteArr));
        Object obj = in.readObject();
        in.close();
        return obj;
    }

    private static byte [] getBlobFromObject(Object obj) throws
java.io.IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        ObjectOutputStream objOut = new ObjectOutputStream(out);
        objOut.writeObject(obj);
        byte [] bytes = out.toByteArray();
        objOut.close();
        return bytes;
    }

    public static void main(String [] args) {
        try {
            Integer i = new Integer(0);
            // it's OK here
            Integer j = (Integer)getObjectFromByteArr(getBlobFromObject(i));
            System.out.println(j);
            // try to convert byte[] to String
            String str = new String(getBlobFromObject(i));
            // and convert it back, exception occurs!!!
            Integer k = (Integer)getObjectFromByteArr(str.getBytes());
            System.out.println(k);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

But it always report a java.io.InvalidClassException, as it seems the
serialVersionUID has been changed when I convert it to String. I have
compared the convert result and the result of String.getBytes(), they
are different. But I have no idea about how to fix it.
What's wrong with it when I convert a byte[] to String? I tried to use
a characterset in creating new String, the problem remains.