生产者发布消息至路由器，未被正确路由时，未设置mandatory参数及ReturnListener监听处理，消息会被broker丢弃，如果不想消息丢失，可以使用备份交换器，这样可以将未被正确路由的消息存储到备份交换机指定的队列。
public static void main(String[] argv) throws Exception { ConnectionFactory factory = new ConnectionFactory(); factory.setHost("localhost"); try (Connection connection = factory.newConnection(); Channel channel = connection.createChannel()) { /** 定义一个备份交换机 和普通交换机无区别 */ channel.exchangeDeclare("alternate_exchange", "fanout", true, false, null); channel.queueDeclare("alternate_queue", true, false, false, null); channel.queueBind("alternate_queue", "alternate_exchange", ""); Map<String, Object> args = new HashMap<>(1); args.put("alternate-exchange", "alternate_exchange"); /** 定义业务交换机 通过参数设置备份交换机 */ channel.exchangeDeclare("biz_exchange", "direct", true, false, args); channel.queueDeclare("biz_queue", true, false, false, null); channel.queueBind("biz_queue", "biz_exchange", "biz_route"); channel.basicPublish("biz_exchange", "biz_route_nil", MessageProperties.PERSISTENT_TEXT_PLAIN, "hello star".getBytes()); } Scanner scanner = new Scanner(System.in); while (scanner.hasNext()) { System.out.println(scanner.next()); } }定义一个本分交换机，与普通交换机无区别，然后在普通业务交换机中使用参数 alternate-exchange 关联备份交换机，此时如果消息未被正常路由，消息将会路由到备份交换机的队列上。 备份交换机建议设置为 fanout ，这样可以避免出现业务消息未被正确路由时，又未能正确匹配备份交换机的绑定队列(如 direct 时)，导致消息丢失。
