在storm中的Bolt中可以处理完成逻辑后，向后面的Blot继续发送消息。

可以发送多个不同的消息，如：

collector.emit("update-delivered-status",new Values(emailDeliverStatus));    collector.emit("save-request",new Values(udsn));

也可以同一个类型的消息发送多个不同内容如;

for (int i = 0; i < emailParamVo.getReceiverNum(); i++)             {                EmailDeliverStatus emailDeliverStatus = new EmailDeliverStatus();                emailDeliverStatus.setCategoryId(emailParamVo.getCategoryId());                emailDeliverStatus.setUpdateTime(emailParamVo.getUpdateTime());                emailDeliverStatus.setStatus(emailParamVo.getEventType());                emailDeliverStatus.setUserId(emailParamVo.getUserId());                emailDeliverStatus.setMessageDetail(emailParamVo.getMessageDetail());                                StringBuilder receiverBuilder = new StringBuilder(emailParamVo.getReceivers());                receiverBuilder = receiverBuilder.deleteCharAt(0);                receiverBuilder = receiverBuilder.deleteCharAt(receiverBuilder.length()-1);                String[] receivers = receiverBuilder.toString().split(" ");                String receiver = receivers[i];                emailDeliverStatus.setEmailId(emailParamVo.getEmailIdPre() + i + "$" + receiver);                emailDeliverStatus.setReceiver(receiver);                collector.emit("update-delivered-status",new Values(emailDeliverStatus));            }

上面的写法是没有问题的，因为for循环里面每次发送的对象都是一个新的实例，但是如果把创建实例的动作放到外面,如：

EmailDeliverStatus emailDeliverStatus = new EmailDeliverStatus();            emailDeliverStatus.setCategoryId(emailParamVo.getCategoryId());            emailDeliverStatus.setUpdateTime(emailParamVo.getUpdateTime());            emailDeliverStatus.setStatus(emailParamVo.getEventType());            emailDeliverStatus.setUserId(emailParamVo.getUserId());            emailDeliverStatus.setMessageDetail(emailParamVo.getMessageDetail());                        for (int i = 0; i < emailParamVo.getReceiverNum(); i++)             {                StringBuilder receiverBuilder = new StringBuilder(emailParamVo.getReceivers());                receiverBuilder = receiverBuilder.deleteCharAt(0);                receiverBuilder = receiverBuilder.deleteCharAt(receiverBuilder.length()-1);                String[] receivers = receiverBuilder.toString().split(" ");                String receiver = receivers[i];                emailDeliverStatus.setEmailId(emailParamVo.getEmailIdPre() + i + "$" + receiver);                emailDeliverStatus.setReceiver(receiver);                collector.emit("update-delivered-status",new Values(emailDeliverStatus));            }

这样就有问题，按照逻辑，我们是想让其emit多个不同emailDeliverStatus对象的消息，但是实际上这样不不行的，因为storm的emit操作并不是立即执行的，

上面的代码就是建立在假设调用emit后，storm就会立即去发送消息。如果按照上面写法，会发现接收消息的bolt收到的for循环中的多个消息都是最后一个消息的重复多次。

因为storm并不是立即执行emit，而是在这个bolt执行的一个固定时间去emit的，所以emailDeliverStatus实例的初始化必须放到for循环的外面执行。

原文地址：http://blog.csdn.net/jsjwk/article/details/8495915