Provides a way to provide custom handling for unknown parameters ni R…

…eflectiveConfigGroup

Fixes #2960

matsim/src/main/java/org/matsim/core/config/ReflectiveConfigGroup.java

@@ -285,14 +285,29 @@ public final void addParam(final String param_name, final String value) {
 			return;
 		}
 
-		Preconditions.checkArgument(storeUnknownParameters, "Module %s of type %s doesn't accept unknown parameters."
-						+ " Parameter %s is not part of the valid parameters: %s", getName(), getClass().getName(), param_name,
-				setters.keySet());
+		this.handleAddUnknownParam(param_name, value);
+	}
+
+	/**
+	 * This method is designed to be overwritten if a config group wants to provide
+	 * custom handling for unknown parameters, e.g. for improved backwards compatibility.
+	 * For example: It allows to convert (old-named) parameter values to different units and
+	 * store them with the new name (old parameter could be km/h, new parameter could be m/s).
+	 *
+	 * The default implementation in {@link ReflectiveConfigGroup} will either store the
+	 * unknown parameter or throw an exception, depending on the value of {@link #storeUnknownParameters}.
+	 *
+	 * If the method is overwritten, it might make sense to also overwrite {@link #handleGetUnknownValue(String)}.
+	 */
+	public void handleAddUnknownParam(final String paramName, final String value) {
+		Preconditions.checkArgument(this.storeUnknownParameters, "Module %s of type %s doesn't accept unknown parameters."
+				+ " Parameter %s is not part of the valid parameters: %s", getName(), getClass().getName(), paramName,
+			this.setters.keySet());
 
 		log.warn(
-				"Unknown parameter {} for group {}. Here are the valid parameter names: {}. Only the string value will be remembered.",
-				param_name, getName(), registeredParams);
-		super.addParam(param_name, value);
+			"Unknown parameter {} for group {}. Here are the valid parameter names: {}. Only the string value will be remembered.",
+			paramName, getName(), this.registeredParams);
+		super.addParam(paramName, value);
 	}
 
 	private void invokeSetter(final Method setter, final String value) {
@@ -438,13 +453,22 @@ public final String getValue(final String param_name) {
 		if (field != null) {
 			return getParamField(field);
 		}
+		return this.handleGetUnknownValue(param_name);
+	}
 
-		Preconditions.checkArgument(storeUnknownParameters, "Module %s of type %s doesn't store unknown parameters."
-						+ " Parameter %s is not part of the valid parameters: %s", getName(), getClass().getName(), param_name,
-				registeredParams);
+	/**
+	 * This method is designed to be overwritten if a config group wants to provide
+	 * custom handling for unknown parameters, e.g. for improved backwards compatibility.
+	 *
+	 * Also see {@link #handleAddUnknownParam(String, String)}
+	 */
+	public String handleGetUnknownValue(final String paramName) {
+		Preconditions.checkArgument(this.storeUnknownParameters, "Module %s of type %s doesn't store unknown parameters."
+						+ " Parameter %s is not part of the valid parameters: %s", getName(), getClass().getName(), paramName,
+				this.registeredParams);
 
-		log.warn("no getter found for param {}: trying parent method", param_name);
-		return super.getValue(param_name);
+		log.warn("no getter found for param {}: trying parent method", paramName);
+		return super.getValue(paramName);
 	}
 
 	private String invokeGetter(Method getter) {