Difficult: How to write a SplitInputStream?

Question

Hi,
I am trying to implement a SplitReader. The basic concept is "shared behavior, cloned data".
Let me explain.. Given a parent InputStream, users can retrieved unlimited amounts of children-inputstreams. These children mirror parent behavior in every possible way. If the parent read() throws a IOInterruptedException after 30 seconds (say the parent is a SockeReader) the children should show the same behavior. This does not mean to say that the moment the parent object throws a IOInterruptedException all children should experience the same; rather, the implementation of the children read() should be identical to the parent read().
Furthermore, while behavior is "shared", the data is distinct. If data is recieved by the parent stream, they are immediately "pushed" into all the children streams. If one child reads off its stream, this does not remove data away from any of the other streams; in this way their state is distinct.
So far, I have managed to implement the data-mirroring aspect of SplitInputStream (ie: each stream gets a copy of the parent data) but I have no idea how to "share" the parent behavior across all children. Ideally I want this class to work for all future subclasses of InputStream which may not exist yet. The behavior "sharing" should be generic enough such that it'll automatically work for all future uses of this class.
Can anyone please help or throw some ideas my way? The more discussion the better!
Thanks,
Gili
(email = [email protected])

Answer 1

I'm not sure that I fully understood what was it that you wanted, but here is my stab at it.
I understood that you want the errors to appear to the children as they appear to the parent stream, but only when the "child" stream encounters that same spot where the error occurs. If so, then what you have to do, is "tag" the spots where the error occured.
These code fragments contain only some relevant code, but should portray the idea.
public ParentStream extends SomeInputStream {
  private String data = "";
  private int errorCode = -1;
  private Hashtable errors = new Hashtable();
  public ChildStream cloneStream() {
      return new ChildStream(data);
  public void doReading() {
      try {
          data += super.read(); // Or whatever...
      } catch(Exception e) {
          errors.put(new Integer(errorCode--),e);
          data += errorCode;
  public Throwable getError(Integer errCode) {
         return errors.get(errCode);
public ChildStream {
    private String data;
    private ParentStream parent;
    int index = 0;
    public ChildStream(ParentStream parent, String data) {
          this.data = data;
          this.parent = parent;
    private int read() {
        int i = data.charAt(index++);
        if(i < 0) { // Error...
           try {
               // This is done using reflection so that the stacktrace will point to the correct
               // place, not the parentstream, but each of the child streams
               Class _cl = Class.forName(parent.getError(new Integer(i)).getClass());
               Constructor const =
                      _cl.getDeclaredConstructor(new Class[]{new String("").getClass()});
                throw (Throwable)const.newInstance(new Object[]{parent.getError(new Integer(i))});
           catch(Exception e) {
               e.printStackTrace();
}Hope this made any sense ;).
Tuomas Rinta