storm-All grouping的应用场景1-发送信号量指令_在apache storm中,何时使用all grouping-优快云博客

本文介绍Apache Storm中AllGrouping的概念及应用场景，通过示例讲解如何使用AllGrouping来实现信号同步，例如缓存刷新等操作。

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All Grouping

from the book：Getting-Started-With-Storm-Jonathan

All Grouping sends a single copy of each tuple to all instances of the receiving bolt.

This kind of grouping is used to send signals to bolts. For example, if you need to refresh a cache, you can send a refresh cache signal to all bolts.

In the word-count example,you could use an all grouping to add the ability to clear the counter cache (see Topol-ogies Example).

将信号的所有tuple发送给所有接收者

用来发送信号量，如发送一个清除 cache的指令

//一个bold 两个输入源
builder.setBolt("word-counter", new WordCounter(),2)
.fieldsGrouping("word-normalizer", new Fields("word"))
.allGrouping("signals-spout","signals");

在bold的execute中做如下判断

public void execute(Tuple input) {String str = null;
try{if(input.getSourceStreamId().equals("signals")){
str = input.getStringByField("action");  if("refreshCache".equals(str))
  counters.clear();
}
}catch (IllegalArgumentException e) {
//Do nothing
}