org.apache.storm.perf.spout

## Class ConstSpout

- java.lang.Object
- - org.apache.storm.topology.base.BaseComponent
  - - org.apache.storm.topology.base.BaseRichSpout
    - - org.apache.storm.perf.spout.ConstSpout

- All Implemented Interfaces:
    Serializable, ISpout, IComponent, IRichSpout

      public class ConstSpout
      extends BaseRichSpout

  See Also:
    Serialized Form

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `ConstSpout(String value)`

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `ack(Object msgId)` Storm has determined that the tuple emitted by this spout with the msgId identifier has been fully processed.
    `void` | `declareOutputFields(OutputFieldsDeclarer declarer)` Declare the output schema for all the streams of this topology.
    `void` | `nextTuple()` When this method is called, Storm is requesting that the Spout emit tuples to the output collector.
    `void` | `open(Map<String,Object> conf, TopologyContext context, SpoutOutputCollector collector)` Called when a task for this component is initialized within a worker on the cluster.
    `ConstSpout` | `withOutputFields(String fieldName)`

    - ### Methods inherited from class org.apache.storm.topology.base.BaseRichSpout

      `activate, close, deactivate, fail`

    - ### Methods inherited from class org.apache.storm.topology.base.BaseComponent

      `getComponentConfiguration`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface org.apache.storm.topology.IComponent

      `getComponentConfiguration`

- - ### Constructor Detail

    - #### ConstSpout

          public ConstSpout(String value)

  - ### Method Detail

    - #### withOutputFields

          public ConstSpout withOutputFields(String fieldName)

    - #### 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

    - #### 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`

Copyright © 2021 The Apache Software Foundation. All rights reserved.