Implementing a Bolt

Bolts must implement the IBolt interface.

public interface IBolt extends Serializable { void prepare(Map heronConf, TopologyContext context, OutputCollector collector); void execute(Tuple input); void cleanup(); }

  • The prepare method is called when the bolt is first initialized and provides the bolt with the executing environment.

  • The execute method is called to process a single input Tuple. The Tuple contains metadata about component/stream/task it comes from. And OutputCollector is used to emit the result.

  • The cleanup method is called before the bolt is shutdown. There’s no guarantee that this method is called due to how the instance is killed.

See ExclamationBolt for a simple bolt example.

Instead of implementing the IBolt interface directly, you can implement IRichBolt.