Question

I have to read a series of object from a binary file.

I use:

ObjectOutputStream obj = new ObjectOutputStream(new FileInputStream(fame));

obj.readObject(p);

where p is a reference to an object I had created. How can I read the entire file until the end?

I can use:

while(p!=null){}

?

Answer 1

Let’s assume you meant ObjectInputStream and p = obj.readObject().

I would do something like this: (this is wrong, see EDIT below)

FileInputStream fstream = new FileInputStream(fileName);
try {
  ObjectInputStream ostream = new ObjectInputStream(fstream);
  while (ostream.available() > 0) {
    Object obj = ostream.readObject();
    // do something with obj
  }
} finally {
  fstream.close();
}

EDIT

I take it back! EJP rightly points out that the use of available() is incorrect here. I think the fixed code might be:

FileInputStream fstream = new FileInputStream(fileName);
try {
  ObjectInputStream ostream = new ObjectInputStream(fstream);
  while (true) {
    Object obj;
    try {
      obj = ostream.readObject();
    } catch (EOFException e) {
      break;
    }
    // do something with obj
  }
} finally {
  fstream.close();
}

Although the documentation for readObject() doesn’t explicitly say that EOFException is thrown at the end of the stream, it seems to be implied and may be the only way to detect the end of the stream.

Another option if you control the code that wrote the stream would be to write an object count at the beginning, or a flag after each object indicating whether the previous object was the final one.