轉：storm中一個Bolt發emit多次相同類型訊息

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在storm中的Bolt中可以處理完成邏輯後，向後面的Blot繼續發送訊息。

可以發送多個不同的訊息，如：

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

也可以同一個類型的訊息發送多個不同內容如;

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));            }

上面的寫法是沒有問題的，因為for迴圈裡面每次發送的對象都是一個新的執行個體，但是如果把建立執行個體的動作放到外面,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));            }

這樣就有問題，按照邏輯，我們是想讓其emit多個不同emailDeliverStatus對象的訊息，但是實際上這樣不不行的，因為storm的emit操作並不是立即執行的，

上面的代碼就是建立在假設調用emit後，storm就會立即去發送訊息。如果按照上面寫法，會發現接收訊息的bolt收到的for迴圈中的多個訊息都是最後一個訊息的重複多次。

因為storm並不是立即執行emit，而是在這個bolt執行的一個固定時間去emit的，所以emailDeliverStatus執行個體的初始化必須放到for迴圈的外面執行。

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

轉：storm中一個Bolt發emit多次相同類型訊息