/**
* Resolve the latest value for the {@link ValueDefinition} from the {@link ConfigurationSource}
* and encapsulate it in a {@link ValueChangeAction} to be enacted in a subsequent operation.
*
* @param valueDefinition the value definition to prepare an update for
* @param configurationSource the source from which to resolve the value.
* @return the change action
* @throws ConfigurationException if any problem occurs retrieving the value.
*/
public ValueChangeAction prepareValueChange(
ValueDefinition<?, ?> valueDefinition, ConfigurationSource configurationSource) {
String expression = valueDefinition.getExpression();
Class<?> type = valueDefinition.getType();
Object result;
boolean available;
if (expression != null) {
available = configurationSource.isAvailable(expression);
} else {
available = configurationSource.isAvailable(type);
}
if (available) {
if (valueDefinition instanceof ValueListDefinition) {
if (expression != null) {
result = configurationSource.retrieveList(expression, type);
} else {
result = configurationSource.retrieveList(type);
}
} else {
if (expression != null) {
result = configurationSource.retrieve(expression, type);
} else {
result = configurationSource.retrieve(type);
}
}
} else if (valueDefinition.isRequired()) {
throw new ValueConfigurationException("No value could be found for", type, expression);
} else {
// Not required and not available, set to null. How this is handled is assignment specific.
result = null;
}
return new ValueChangeAction(valueDefinition, result);
}
/**
* Carry out the change to the value by invoking the {@link ValueChangeListener} with the value
* resolved by {@link #prepareValueChange(ValueDefinition, ConfigurationSource)}.
*
* @param valueChangeAction the action to perform
* @throws ValueConfigurationException if the listener throws a {@link RuntimeException}.
*/
@SuppressWarnings({"rawtypes", "unchecked"})
public void enactValueChange(ValueChangeAction valueChangeAction) {
ValueDefinition<?, ?> valueDefinition = valueChangeAction.getValueDefinition();
Object newValue = valueChangeAction.getNewValue();
Object oldValue = valueChangeAction.getOldValue();
ValueChangeListener listener = valueDefinition.getChangeListener();
try {
listener.onChange(newValue, oldValue);
} catch (RuntimeException e) {
throw new ValueConfigurationException(
"value assignment", valueDefinition.getType(), valueDefinition.getExpression(), e);
}
}