Implemented SessionListenerCollection - a simple auto-populating collection of instances of all available listeners.

guacamole/src/main/java/net/sourceforge/guacamole/net/basic/event/SessionListenerCollection.java

@@ -0,0 +1,110 @@
+package net.sourceforge.guacamole.net.basic.event;
+
+import java.lang.reflect.InvocationTargetException;
+import java.util.AbstractCollection;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Iterator;
+import javax.servlet.http.HttpSession;
+import net.sourceforge.guacamole.GuacamoleException;
+import net.sourceforge.guacamole.net.basic.GuacamoleClassLoader;
+
+/**
+ * A collection which iterates over instances of all listeners defined in
+ * guacamole.properties. For each listener defined in guacamole.properties, a
+ * new instance is created and stored in this collection. The contents of this
+ * collection is stored within the HttpSession, and will be reused if available.
+ * Each listener is instantiated once per session. Listeners are singleton
+ * classes within the session, but not globally.
+ * 
+ * @author Michael Jumper
+ */
+public class SessionListenerCollection extends AbstractCollection {
+
+    /**
+     * The name of the session attribute which will contain the listener
+     * collection.
+     */
+    private static final String SESSION_ATTRIBUTE = "__GUAC_LISTENERS";
+
+    /**
+     * The wrapped collection of listeners, possibly retrieved from the
+     * session.
+     */
+    private Collection listeners;
+    
+    /**
+     * Creates a new SessionListenerCollection which stores all listeners
+     * defined in guacamole.properties in the provided session. If listeners
+     * are already stored in the provided session, those listeners are used
+     * instead.
+     * 
+     * @param session The HttpSession to store listeners within.
+     * @throws GuacamoleException If an error occurs while instantiating new
+     *                            listeners.
+     */
+    public SessionListenerCollection(HttpSession session) throws GuacamoleException {
+        
+        // Pull cached listeners from session
+        listeners = (Collection) session.getAttribute(SESSION_ATTRIBUTE);
+
+        // If no listeners stored, listeners must be loaded first
+        if (listeners == null) {
+
+            // Load listeners from guacamole.properties
+            listeners = new ArrayList();
+            try {
+
+                // TODO: Retrieve list of listener classnames from properties
+                Class listenerClass = GuacamoleClassLoader.getInstance().loadClass(
+                        "net.sourceforge.guacamole.test.GenericLoggingListener"
+                );
+
+                // Instantiate listener
+                Object listener = listenerClass.getConstructor().newInstance();
+
+                // Add listener to collection of listeners
+                listeners.add(listener);
+
+            }
+            catch (ClassNotFoundException e) {
+                throw new GuacamoleException("Could not find listener class.", e);
+            }
+            catch (InstantiationException e) {
+                throw new GuacamoleException("Listener class is abstract.", e);
+            }
+            catch (IllegalAccessException e) {
+                throw new GuacamoleException("No access to listener constructor.", e);
+            }
+            catch (IllegalArgumentException e) {
+                // This should not happen, given there ARE no arguments
+                throw new GuacamoleException("Illegal arguments to listener constructor.", e);
+            }
+            catch (InvocationTargetException e) {
+                throw new GuacamoleException("Error while instantiating listener.", e);
+            }
+            catch (NoSuchMethodException e) {
+                throw new GuacamoleException("Listener has no default constructor.", e);
+            }
+            catch (SecurityException e) {
+                throw new GuacamoleException("Security restrictions prevent instantiation of listener.", e);
+            }
+
+            // Store listeners for next time
+            session.setAttribute(SESSION_ATTRIBUTE, listeners);
+            
+        }
+        
+    }
+    
+    @Override
+    public Iterator iterator() {
+        return listeners.iterator();
+    }
+
+    @Override
+    public int size() {
+        return listeners.size();
+    }
+    
+}