(no commit message)

[utils] / support / general / src / main / java / org / wamblee / observer / Observable.java

diff --git a/support/general/src/main/java/org/wamblee/observer/Observable.java b/support/general/src/main/java/org/wamblee/observer/Observable.java
new file mode 100644 (file)
index 0000000..2980afa
--- /dev/null
+++ b/support/general/src/main/java/org/wamblee/observer/Observable.java
@@ -0,0 +1,146 @@
+/*
+ * Copyright 2005 the original author or authors.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.wamblee.observer;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Map;
+import java.util.TreeMap;
+
+import org.apache.log4j.Logger;
+
+/**
+ * Implements subscription and notification logic for an observer pattern. This
+ * class is thread safe.
+ */
+public class Observable<ObservableType, Event> {
+
+    private static final Logger LOGGER = Logger.getLogger(Observable.class);
+
+    /**
+     * Observable.
+     */
+    private ObservableType _observable;
+
+    /**
+     * Used to notify observers.
+     */
+    private ObserverNotifier<ObservableType, Event> _notifier;
+
+    /**
+     * Map of subscription to observer.
+     */
+    private Map<Long, Observer<ObservableType, Event>> _observers;
+
+    /**
+     * Counter for subscriptions. Holds the next subscription.
+     */
+    private long _counter;
+
+    /**
+     * Constructs the observable.
+     * 
+     * @param aObservable
+     *            Observable this instance is used for.
+     * @param aNotifier
+     *            Object used for implementing notification of listeners.
+     */
+    public Observable(ObservableType aObservable,
+            ObserverNotifier<ObservableType, Event> aNotifier) {
+        _observable = aObservable;
+        _notifier = aNotifier;
+        _observers = new TreeMap<Long, Observer<ObservableType, Event>>();
+        _counter = 0;
+    }
+
+    /**
+     * Subscribe an obvers.
+     * 
+     * @param aObserver
+     *            Observer to subscribe.
+     * @return Event Event to send.
+     */
+    public synchronized long subscribe(Observer<ObservableType, Event> aObserver) {
+        long subscription = _counter++; // integer rage is so large it will
+                                        // never roll over.
+        _observers.put(subscription, aObserver);
+        return subscription;
+    }
+
+    /**
+     * Unsubscribe an observer.
+     * 
+     * @param aSubscription
+     *            Subscription which is used
+     * @throws IllegalArgumentException
+     *             In case the subscription is not known.
+     */
+    public synchronized void unsubscribe(long aSubscription) {
+        Object obj = _observers.remove(aSubscription);
+        if (obj == null) {
+            throw new IllegalArgumentException("Subscription '" + aSubscription
+                    + "'");
+        }
+    }
+
+    /**
+     * Gets the number of subscribed observers.
+     * 
+     * @return Number of subscribed observers.
+     */
+    public int getObserverCount() {
+        return _observers.size();
+    }
+
+    /**
+     * Notifies all subscribed observers.
+     * 
+     * @param aEvent
+     *            Event to send.
+     */
+    public void send(Event aEvent) {
+        // Make sure we do the notification while not holding the lock to avoid
+        // potential deadlock
+        // situations.
+        List<Observer<ObservableType, Event>> observers = new ArrayList<Observer<ObservableType, Event>>();
+        synchronized (this) {
+            observers.addAll(_observers.values());
+        }
+        for (Observer<ObservableType, Event> observer : observers) {
+            _notifier.update(observer, _observable, aEvent);
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     * 
+     * @see java.lang.Object#finalize()
+     */
+    @Override
+    protected void finalize() throws Throwable {
+        if (_observers.size() > 0) {
+            LOGGER
+                    .error("Still observers registered at finalization of observer!");
+            for (Observer observer : _observers.values()) {
+                LOGGER.error("  observer: " + observer);
+            }
+        }
+
+        super.finalize();
+    }
+
+}