@Override
    protected void onInit() throws Exception {
        if (!this.evaluationContextSet) {
            this.evaluationContext = IntegrationContextUtils.getEvaluationContext(getBeanFactory());
        }
    }
Construct a new MessageHandler given the reactor based Processor to delegate
processing to and a partition expression.

@param processor The stream based reactor processor
spring-xd-reactor/src/main/java/org/springframework/xd/reactor/MultipleBroadcasterMessageHandler.java