001 package de.deepamehta.core.impl;
002
003 import de.deepamehta.core.osgi.PluginContext;
004 import de.deepamehta.core.service.DeepaMehtaEvent;
005 import de.deepamehta.core.service.DeepaMehtaService;
006 import de.deepamehta.core.service.EventListener;
007
008 import javax.ws.rs.WebApplicationException;
009
010 import java.util.ArrayList;
011 import java.util.HashMap;
012 import java.util.List;
013 import java.util.Map;
014
015
016
017 class EventManager {
018
019 // ---------------------------------------------------------------------------------------------- Instance Variables
020
021 /**
022 * The registered event listeners (key: event class name, value: event listeners).
023 */
024 private Map<String, List<EventListener>> listenerRegistry = new HashMap();
025
026 private DeepaMehtaService dms;
027
028 // ---------------------------------------------------------------------------------------------------- Constructors
029
030 EventManager(DeepaMehtaService dms) {
031 this.dms = dms;
032 // Note: actually the class CoreEvent does not need to be instantiated as it contains only statics.
033 // But if not instantiated OSGi apparently does not load the class at all.
034 new CoreEvent();
035 }
036
037 // ----------------------------------------------------------------------------------------- Package Private Methods
038
039 void addListener(DeepaMehtaEvent event, EventListener listener) {
040 List<EventListener> listeners = getListeners(event);
041 if (listeners == null) {
042 listeners = new ArrayList();
043 putListeners(event, listeners);
044 }
045 listeners.add(listener);
046 }
047
048 void removeListener(DeepaMehtaEvent event, EventListener listener) {
049 List<EventListener> listeners = getListeners(event);
050 if (!listeners.remove(listener)) {
051 throw new RuntimeException("Removing " + listener + " from " +
052 event + " event listeners failed: not found in " + listeners);
053 }
054 }
055
056 // ---
057
058 void fireEvent(DeepaMehtaEvent event, Object... params) {
059 List<EventListener> listeners = getListeners(event);
060 if (listeners != null) {
061 for (EventListener listener : listeners) {
062 deliverEvent(listener, event, params);
063 }
064 }
065 }
066
067 // ---
068
069 /**
070 * Checks weather the given plugin is a listener for the given event, and if so, delivers the event to the plugin.
071 * Otherwise nothing is performed.
072 */
073 void deliverEvent(PluginImpl plugin, DeepaMehtaEvent event, Object... params) {
074 PluginContext pluginContext = plugin.getContext();
075 if (!isListener(pluginContext, event)) {
076 return;
077 }
078 //
079 deliverEvent((EventListener) pluginContext, event, params);
080 }
081
082 /**
083 * Convenience method to check weather the specified plugin is a listener for the given event, and if so,
084 * delivers the event to the plugin. Otherwise nothing is performed.
085 */
086 void deliverEvent(String pluginUri, DeepaMehtaEvent event, Object... params) {
087 deliverEvent((PluginImpl) dms.getPlugin(pluginUri), event, params);
088 }
089
090 // ------------------------------------------------------------------------------------------------- Private Methods
091
092 private void deliverEvent(EventListener listener, DeepaMehtaEvent event, Object... params) {
093 try {
094 event.deliver(listener, params);
095 } catch (WebApplicationException e) {
096 // Note: a WebApplicationException thrown by a event listener must reach Jersey. So we re-throw here.
097 // This allow plugins to produce specific HTTP responses by throwing a WebApplicationException.
098 // Consider the Caching plugin: it produces a possible 304 (Not Modified) response this way.
099 throw e;
100 } catch (Exception e) {
101 throw new RuntimeException("Processing event " + event + " by " + listener + " failed", e);
102 }
103 }
104
105 // ---
106
107 /**
108 * Returns true if the given plugin is a listener for the given event.
109 */
110 private boolean isListener(PluginContext pluginContext, DeepaMehtaEvent event) {
111 return event.getListenerInterface().isAssignableFrom(pluginContext.getClass());
112 }
113
114 // ---
115
116 private List<EventListener> getListeners(DeepaMehtaEvent event) {
117 return listenerRegistry.get(event.getClass().getName());
118 }
119
120 private void putListeners(DeepaMehtaEvent event, List<EventListener> listeners) {
121 listenerRegistry.put(event.getClass().getName(), listeners);
122 }
123 }