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Subject: Re: [sca-j] Comparing ServiceRefernces and CallbackReferences using equals() method
"Mark Combellack"
<mcombellack@avaya.com>
20/05/2008 11:18 |
|
One of our SCA users has just asked whether it is OK to call equals() on ServiceReferences and CallbackReferences to compare whether two references refer to the same target. I had a quick skim through the Java Specifications but I did not find anything.
I’m interested as to whether the equals() method on ServiceReferences has been previously discussed and whether the TC feels that it is worth opening an issue for it.
I’ve distilled the main points of what the user wanted to do and illustrated it with a small sample as described below.
The problem is to make sure that a client does not register more than once to receive progress notifications, the DownloadService implementation needs to be able to compare ServiceReferences using the standard Java equals() method as shown by the code below:
public class DownloadServiceImpl implements DownloadService {
private final Map<String, List<ServiceReference<DownloadServiceNotification>>> listeners
= new HashMap<String, List<ServiceReference<DownloadServiceNotification>>>();
public synchronized void addListener(
String downloadID, ServiceReference<DownloadServiceNotification> newListener) {
final List<ServiceReference<DownloadServiceNotification>> downloadListeners
= listeners.get(downloadID);
if (downloadListeners == null) {
// listener for a download that has no listeners so add one.
// Code not shown.....
} else {
// Is the listener already registered
for (ServiceReference<DownloadServiceNotification> l : downloadListeners) {
// *********
// PROBLEM IS HERE. Can I call equals() on a ServiceReference?
// *********
if (l.equals(newListener)) {
// Already registered so ignore request
return;
}
}
// Not registered so add
downloadListeners.add(newListener);
}
}
I believe what the user wants the equals() method to do is the following. Two ServiceReferences/CallbackReferences are equal if:
Below this point, I have included some sample code fragments that may or may not be useful in illustrating what the user wants to do. Feel free to skip the rest of the email if you feel the problem is already well defined.
The Download Service interface would end up being something like:
public interface DownloadService {
// Returns a downloadID
String download(URL url);
void addListener(String downloadID, ServiceReference<DownloadServiceNotification> listener);
void removeListener(String downloadID, ServiceReference<DownloadServiceNotification> listener);
boolean isDownloadCompleted(String downloadID);
}
The DownloadServiceNotification interface would be something like:
public interface DownloadServiceNotification {
// Download is waiting in queue to be downloaded
void queued(String id);
// Download has started
void started(String id);
// Download progress notification
void progress(String id, int percentageComplete);
// Download completed
void completed(String id);
}
The client code would want to do something similar to:
public class Client implements DownloadServiceNotification {
@Context
protected ComponentContext componentContext;
@Reference
protected DownloadService downloadService;
public void download(URL url) {
final String downloadID = downloadService.download(url);
// wait 10 seconds to see if the download is completed
sleep(10);
if (downloadService.isDownloadCompleted(downloadID)) {
// Download completed
return;
}
// Download not complete so register a listener and handle asynchronously
final ServiceReference<DownloadServiceNotification> self
= componentContext.createSelfReference(DownloadServiceNotification.class);
downloadService.addListener(downloadID, self);
}
}
Thanks,
Mark
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