Changed dependency injection of player implementation so that a missing library falls back to another engine.

src/main/java/musicplayer/SwingUIModule.java

@@ -1,20 +1,18 @@
 package musicplayer;
 
 import com.google.inject.AbstractModule;
-import com.google.inject.Provides;
 import com.google.inject.Singleton;
 import musicplayer.callbacks.PlayerCallbackInterface;
 import musicplayer.db.HibernateDatabase;
 import musicplayer.db.IDatabase;
 import musicplayer.library.ILibrary;
 import musicplayer.library.JTreeLibrary;
-import musicplayer.player.GStreamerPlayer;
 import musicplayer.player.IPlayer;
-import musicplayer.player.VLCPlayer;
 import musicplayer.playlist.IPlaylist;
 import musicplayer.playlist.TabbedJTablePlaylist;
 import musicplayer.swingui.PlayerGUI;
 import musicplayer.util.ConfigManager;
+import musicplayer.util.Engine;
 
 /**
  * Dependency injection setup using Swing UI Components.
@@ -24,19 +22,26 @@ class SwingUIModule extends AbstractModule {
     @Override
     protected void configure() {
         bind(IDatabase.class).to(HibernateDatabase.class).in(Singleton.class);
-        bind(IPlaylist.class).to(TabbedJTablePlaylist.class).in(Singleton.class);
-        bind(ILibrary.class).to(JTreeLibrary.class).in(Singleton.class);
+        bind(IPlaylist.class).to(TabbedJTablePlaylist.class);
+        bind(ILibrary.class).to(JTreeLibrary.class);
         bind(PlayerCallbackInterface.class).to(PlayerGUI.class);
-    }
-
-    @Provides
-    @Singleton
-    private IPlayer providePlayer(GStreamerPlayer gStreamerPlayer, VLCPlayer vlcPlayer){
         String engineName = ConfigManager.getPlayerEngine();
-        switch (engineName){
-            case "GStreamer": return gStreamerPlayer;
-            case "VLC": return vlcPlayer;
-            default: return gStreamerPlayer;
+        boolean engineSet = false;
+        for(Engine engine : Engine.values()){
+            if(engineName.equals(engine.getEngineName()) && engine.isAvailable()){
+                bind(IPlayer.class).to(engine.getEngineImplementation());
+                ConfigManager.setPlayerEngine(engine.getEngineName());
+                engineSet = true;
+            }
+        }
+        if(!engineSet){ // If the user has set an invalid engine, try and set a usable one.
+            for(Engine engine : Engine.values()){
+                if(engine.isAvailable()){
+                    bind(IPlayer.class).to(engine.getEngineImplementation());
+                    ConfigManager.setPlayerEngine(engine.getEngineName());
+                    break;
+                }
+            }
         }
     }
 }

src/main/java/musicplayer/util/ConfigManager.java

@@ -25,7 +25,7 @@ public final class ConfigManager {
     private static final String libraryDisplayKey = "libraryDisplayKey";
     private static final String lastVolumeKey = "volume";
     private static final String engineKey = "engine";
-    public static final String[] engineNames = {"GStreamer", "VLC"};
+    public static final String[] engineNames = Engine.engineList();
 
     /**
      * @return List of directories used for music library indexing.

src/main/java/musicplayer/util/Engine.java

@@ -0,0 +1,62 @@
+package musicplayer.util;
+
+import musicplayer.player.GStreamerPlayer;
+import musicplayer.player.IPlayer;
+import musicplayer.player.VLCPlayer;
+
+/**
+ * Available playback engines.
+ */
+public enum Engine {
+
+    GSTREAMER("GStreamer", GStreamerPlayer.class, "org.gstreamer.elements.PlayBin2"),
+    VLC("VLC", VLCPlayer.class, "uk.co.caprica.vlcj.player.MediaPlayer");
+
+    private final String engineName;
+    private final Class<? extends IPlayer> engineImplementation;
+    private final String neededClass;
+
+    Engine(String engineName, Class<? extends IPlayer> engineImplementation, String neededClass) {
+        this.engineName = engineName;
+        this.engineImplementation = engineImplementation;
+        this.neededClass = neededClass;
+    }
+
+    /**
+     * @return Name of the engine.
+     */
+    public String getEngineName() {
+        return engineName;
+    }
+
+    /**
+     * @return Class used as the implementation for this engine.
+     */
+    public Class<? extends IPlayer> getEngineImplementation() {
+        return engineImplementation;
+    }
+
+    /**
+     * @return List of all available engines.
+     */
+    public static String[] engineList(){
+        String[] engineList = new String[Engine.values().length];
+        for(int i = 0; i < engineList.length; i++){
+            engineList[i] = Engine.values()[i].getEngineName();
+        }
+        return engineList;
+    }
+
+    /**
+     * @return Whether the needed library for this playback engine is available.
+     */
+    public boolean isAvailable() {
+        try {
+            Class.forName(neededClass);
+            return true;
+        } catch (ClassNotFoundException ignored) {
+            System.out.println("Couldn't load " + neededClass);
+        }
+        return false;
+    }
+}