@Override
                    public MessageProducer call() throws Exception {
                        MessageProducer producer = MetaqTemplate.this.messageSessionFactory.createProducer();
                        producer.publish(topic);
                        if (!StringUtils.isBlank(MetaqTemplate.this.defaultTopic)) {
                            producer.setDefaultTopic(MetaqTemplate.this.defaultTopic);
                        }
                        return producer;
                    }
Returns or create a message producer for topic.

@param topic
@return
@since 1.4.5
metamorphosis-client/src/main/java/com/taobao/metamorphosis/client/extension/spring/MetaqTemplate.java