Added the ability to recover from engine incompatibilities.

ProtocolLib/src/main/java/com/comphenix/protocol/CommandFilter.java

@@ -220,16 +220,44 @@ public class CommandFilter extends CommandBase {
 	}
 	
 	private void initalizeScript() {
+		try {
+			// First attempt
+			initializeEngine();
+		} catch (ScriptException e1) {
+			// It's not a huge deal
+			printPackageWarning(e1);
+			
+			if (!config.getScriptEngineName().equals("rhino")) {
+				reporter.reportWarning(this, "Falling back to the Rhino engine.");
+				config.setScriptEngineName("rhino");
+				config.saveAll();
+				
+				try {
+					initializeEngine();
+				} catch (ScriptException e2) {
+					// And again ..
+					printPackageWarning(e2);
+				}
+			}
+		}
+	}
+	
+	private void printPackageWarning(ScriptException e) {
+		reporter.reportWarning(this, "Unable to initialize packages for JavaScript engine.", e);
+	}
+	
+	/**
+	 * Initialize the current configured engine.
+	 * @throws ScriptException If we are unable to import packages.
+	 */
+	private void initializeEngine() throws ScriptException {
 		ScriptEngineManager manager = new ScriptEngineManager();
-		engine = manager.getEngineByName("JavaScript");
+		engine = manager.getEngineByName(config.getScriptEngineName());
 		
 		// Import useful packages
-		try {
 		engine.eval("importPackage(org.bukkit);");
 		engine.eval("importPackage(com.comphenix.protocol.reflect);");
-		} catch (ScriptException e) {
+			
-			throw new IllegalStateException("Unable to initialize packages for JavaScript engine.", e);
-		}
 	}
 
 	/**

ProtocolLib/src/main/java/com/comphenix/protocol/ProtocolConfig.java

@@ -41,9 +41,10 @@ class ProtocolConfig {
 	private static final String BACKGROUND_COMPILER_ENABLED = "background compiler";
 
 	private static final String DEBUG_MODE_ENABLED = "debug";
-	
 	private static final String INJECTION_METHOD = "injection method";
 	
+	private static final String SCRIPT_ENGINE_NAME = "script engine";
+	
 	private static final String UPDATER_NOTIFY = "notify";
 	private static final String UPDATER_DOWNLAD = "download";
 	private static final String UPDATER_DELAY = "delay";
@@ -257,6 +258,24 @@ class ProtocolConfig {
 		updater.set(UPDATER_LAST_TIME, lastTimeSeconds);
 	}
 	
+	/**
+	 * Retrieve the unique name of the script engine to use for filtering.
+	 * @return Script engine to use.
+	 */
+	public String getScriptEngineName() {
+		return global.getString(SCRIPT_ENGINE_NAME, "JavaScript");
+	}
+	
+	/**
+	 * Set the unique name of the script engine to use for filtering.
+	 * <p>
+	 * This setting will take effect next time ProtocolLib is started.
+	 * @param name - name of the script engine to use.
+	 */
+	public void setScriptEngineName(String name) {
+		global.set(SCRIPT_ENGINE_NAME, name);
+	}
+	
 	/**
 	 * Retrieve the default injection method.
 	 * @return Default method.

ProtocolLib/src/main/resources/config.yml

@@ -22,3 +22,6 @@ global:
   
   # Whether or not to enable the filter command
   debug: false
+  
+  # The engine used by the filter command
+  script engine: JavaScript