Package org.apache.storm.spout

Class CheckpointSpout

java.lang.Object
org.apache.storm.topology.base.BaseComponent
org.apache.storm.topology.base.BaseRichSpout
org.apache.storm.spout.CheckpointSpout
All Implemented Interfaces:
Serializable, ISpout, IComponent, IRichSpout
public class CheckpointSpout extends BaseRichSpout
Emits checkpoint tuples which is used to save the state of the IStatefulComponent across the topology. If a topology contains Stateful bolts, Checkpoint spouts are automatically added to the topology. There is only one Checkpoint task per topology. Checkpoint spout stores its internal state in a KeyValueState.
See Also:

  • Field Details

  • Constructor Details

    • CheckpointSpout

      public CheckpointSpout()

  • Method Details

    • isCheckpoint

      public static boolean isCheckpoint(Tuple input)

    • open

      public void open(Map<String,Object> conf, TopologyContext context, SpoutOutputCollector collector)
      Description copied from interface: ISpout
      Called when a task for this component is initialized within a worker on the cluster. It provides the spout with the environment in which the spout executes.

      This includes the:

      Parameters:
      conf - The Storm configuration for this spout. This is the configuration provided to the topology merged in with cluster configuration on this machine.
      context - This object can be used to get information about this task's place within the topology, including the task id and component id of this task, input and output information, etc.
      collector - The collector is used to emit tuples from this spout. Tuples can be emitted at any time, including the open and close methods. The collector is thread-safe and should be saved as an instance variable of this spout object.

    • nextTuple

      public void nextTuple()
      Description copied from interface: ISpout
      When this method is called, Storm is requesting that the Spout emit tuples to the output collector. This method should be non-blocking, so if the Spout has no tuples to emit, this method should return. nextTuple, ack, and fail are all called in a tight loop in a single thread in the spout task. When there are no tuples to emit, it is courteous to have nextTuple sleep for a short amount of time (like a single millisecond) so as not to waste too much CPU.

    • ack

      public void ack(Object msgId)
      Description copied from interface: ISpout
      Storm has determined that the tuple emitted by this spout with the msgId identifier has been fully processed. Typically, an implementation of this method will take that message off the queue and prevent it from being replayed.
      Specified by:
      ack in interface ISpout
      Overrides:
      ack in class BaseRichSpout

    • fail

      public void fail(Object msgId)
      Description copied from interface: ISpout
      The tuple emitted by this spout with the msgId identifier has failed to be fully processed. Typically, an implementation of this method will put that message back on the queue to be replayed at a later time.
      Specified by:
      fail in interface ISpout
      Overrides:
      fail in class BaseRichSpout

    • declareOutputFields

      public void declareOutputFields(OutputFieldsDeclarer declarer)
      Description copied from interface: IComponent
      Declare the output schema for all the streams of this topology.
      Parameters:
      declarer - this is used to declare output stream ids, output fields, and whether or not each output stream is a direct stream