How to append Objects in a file.

Question

i have the following sample code ,
its not read data properly and throws Stream Corrupted Exception in the appended record. ( at Last statement of try block ).
Thanks,
import java.io.*;
public class IOError {
public static void main(String[] args) {
try {
ObjectOutputStream oos = new ObjectOutputStream(
new FileOutputStream("data.dat"));
oos.writeObject(new String("string 1"));
oos.writeObject(new String("string 2"));
oos.flush();
oos.close();
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("data.dat"));
System.out.println("----- Round 1 Starts ---------");
System.out.println((String) ois.readObject());
System.out.println((String) ois.readObject());
ois.close();
ObjectOutputStream oos2 = new ObjectOutputStream(
new FileOutputStream("data.dat",true)); // Appending Data
oos2.writeObject(new String("string 3"));
oos2.flush();
oos2.close();
ObjectInputStream ois2 = new ObjectInputStream(new FileInputStream("data.dat"));
System.out.println("----- Round 2 Starts ---------");
System.out.println((String) ois2.readObject());
System.out.println((String) ois2.readObject());
System.out.println((String) ois2.readObject()); // Stream Corrupted Exception
catch(Exception e) {
System.out.println(e);

Answer 1

Nasty. When you open an ObjectOutputStream, it will write a few initializing bytes, so if you really want to append objects to a file, then after you read the first two strings, you need to create a new ObjectInputStream that will read those bytes.
You could write an object indicating that now you are done with this ObjectOutputStream, so when you read the file and read this object, you know you have to create a new ObjectInputStream.
oos.writeObject(new String("string 1"));
oos.writeObject(new String("string 2"));
oos.writeObject(null); // null could be used if you know you won't write any other null's in your code.
//... append
oos.writeObject(new String("string 3"));
oos.writeObject(null);
// read:
FileInputStream fis = new FileInputStream("data.dat");
ObjectInputStream ois2 = new ObjectInputStream(fis);
String s;
while ((s = (String)ois2.readObject()) != null) {
  System.out.println(s);
ois2 = new ObjectInputStream(fis);
while ((s = (String)ois2.readObject()) != null) {
  System.out.println(s);