转：storm中一个Bolt发emit多次相同类型消息

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