RandomFileAccess-java.io.StreamCorruptedException

Question

I am trying to read 'n' bytes (serialized object) from file starting from position 'i' using. Here is my code snippet below,

public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchAlgorithmException {
      String s = "XYZ";
      RandomAccessFile f = new RandomAccessFile("/home/Test.txt", "rw");
      f.write(s.getBytes());
      FingerPrint finger = new FingerPrint("ABCDEFG", "ABCD.com");
      Serializer ser = new Serializer();
      byte[] key = ser.serialize(finger);//Serializing the object
      f.seek(3);
      f.write(key);
      byte[] new1 = new byte[(int)f.length()-3];
      int i=0;
      for(i=3;f.read()!=-1;i++){
        f.seek(i);
        new1[i]=f.readByte();
      }
      FingerPrint finger2 = (FingerPrint) ser.deserialize(new1);//deserializing it
      System.out.println("After reading:"+finger2.getURL());
}

I am getting following exception,

 Exception in thread "main" java.io.StreamCorruptedException: invalid stream header: 00000000
at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:807)
at java.io.ObjectInputStream.<init>(ObjectInputStream.java:302)

Here is my serializer class,

class Serializer {

public static byte[] serialize(Object obj) throws IOException {
    try(ByteArrayOutputStream b = new ByteArrayOutputStream()){
        try(ObjectOutputStream o = new ObjectOutputStream(b)){
            o.writeObject(obj);
        }
        return b.toByteArray();
    }
}

public static Object deserialize(byte[] bytes) throws IOException, ClassNotFoundException {
    try(ByteArrayInputStream b = new ByteArrayInputStream(bytes)){
        try(ObjectInputStream o = new ObjectInputStream(b)){
            return o.readObject();
        }
    }
}

}

If i don't write any string to the file, and only read the object ie start from 0 to eof, i am able to see the output. There are many such questions already asked but i want to know why it is not working when i write a object in particular location and read it back. May be i am doing something wrong, Please share your thoughts.

Answer 1

Here is your problem:

  f.seek(3);
  f.write(key);
  byte[] new1 = new byte[(int)f.length()-3];
  int i=0;
  for(i=3;f.read()!=-1;i++){
          ^^^^^^^^

At this point the file pointer is at EOF since you just wrote the serialized bytes and have not moved the file pointer yet. This loop is unnecessary, you should seek(3) and then read directly into new1 as in

byte[] new1 = new byte[(int) f.length() - 3];
f.seek(3);
f.read(new1);
FingerPrint finger2 = (FingerPrint) ser.deserialize(new1);// deserializing