Hello everyone,
Currently, I have one observable and many observers. What i need is different observables, and depending on the observable, different observers. How do I achieve this? ( For understanding, assume I have different apples - say apple1 apple2... I have observer_1 observing apple1, observer_2 observing apple2, observer_3 observing apple 2 and so on..). I tried creating different objects of the Observable class, but since observers are observing the same class of observable, I don't know how to access a particular instance of the Observable.
I have included the following servlet code that contains Observer and Observable classes:
public class CustomerServlet extends HttpServlet {
public String getNextMessage() {
// Create a message sink to wait for a new message from the
// message source.
return new MessageSink().getNextMessage(source);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream());
String recMSG = getNextMessage();
dout.writeObject(recMSG);
dout.flush();
}
public void broadcastMessage(String message) {
// Send the message to all the HTTP-connected clients by giving the
// message to the message source
source.sendMessage(message);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
ObjectInputStream din= new ObjectInputStream(request.getInputStream());
String message = (String)din.readObject();
ObjectOutputStream dout = new ObjectOutputStream(response.getOutputStream());
dout.writeObject("1");
dout.flush();
if (message != null) {
broadcastMessage(message);
}
// Set the status code to indicate there will be no response
response.setStatus(response.SC_NO_CONTENT);
} catch (Exception e) {
e.printStackTrace();
}
}
@Override
public String getServletInfo() {
return "Short description";
}// </editor-fold>
MessageSource source = new MessageSource();
}
class MessageSource extends Observable {
public void sendMessage(String message) {
setChanged();
notifyObservers(message);
}
}
class MessageSource extends Observable {
public void sendMessage(String message) {
setChanged();
notifyObservers(message);
}
}
class MessageSink implements Observer {
String message = null; // set by update() and read by getNextMessage()
// Called by the message source when it gets a new message
synchronized public void update(Observable o, Object arg) {
// Get the new message
message = (String)arg;
// Wake up our waiting thread
notify();
}
// Gets the next message sent out from the message source
synchronized public String getNextMessage(MessageSource source) {
// Tell source we want to be told about new messages
source.addObserver(this);
// Wait until our update() method receives a message
while (message == null) {
try {
wait();
} catch (Exception e) {
System.out.println("Exception has occured! ERR ERR ERR");
}
}
// Tell source to stop telling us about new messages
source.deleteObserver(this);
// Now return the message we received
// But first set the message instance variable to null
// so update() and getNextMessage() can be called again.
String messageCopy = message;
message = null;
return messageCopy;
}
}
