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java.lang.Object backtype.storm.task.ShellBolt
public class ShellBolt
A bolt that shells out to another process to process tuples. ShellBolt communicates with that process over stdio using a special protocol. An ~100 line library is required to implement that protocol, and adapter libraries currently exist for Ruby and Python.
To run a ShellBolt on a cluster, the scripts that are shelled out to must be in the resources directory within the jar submitted to the master. During development/testing on a local machine, that resources directory just needs to be on the classpath.
When creating topologies using the Java API, subclass this bolt and implement the IRichBolt interface to create components for the topology that use other languages. For example:
public class MyBolt extends ShellBolt implements IRichBolt { public MyBolt() { super("python", "mybolt.py"); } public void declareOutputFields(OutputFieldsDeclarer declarer) { declarer.declare(new Fields("field1", "field2")); } }
Field Summary | |
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static Logger |
LOG
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Constructor Summary | |
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ShellBolt(ShellComponent component)
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Method Summary | |
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void |
cleanup()
Called when an IBolt is going to be shutdown. |
void |
execute(Tuple input)
Process a single tuple of input. |
void |
prepare(java.util.Map stormConf,
TopologyContext context,
OutputCollector collector)
Called when a task for this component is initialized within a worker on the cluster. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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public static Logger LOG
Constructor Detail |
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public ShellBolt(ShellComponent component)
Method Detail |
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public void prepare(java.util.Map stormConf, TopologyContext context, OutputCollector collector)
IBolt
This includes the:
prepare
in interface IBolt
stormConf
- The Storm configuration for this bolt. 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 bolt. Tuples can be emitted at any time, including the prepare and cleanup methods. The collector is thread-safe and should be saved as an instance variable of this bolt object.public void execute(Tuple input)
IBolt
Tuples should be emitted using the OutputCollector provided through the prepare method. It is required that all input tuples are acked or failed at some point using the OutputCollector. Otherwise, Storm will be unable to determine when tuples coming off the spouts have been completed.
For the common case of acking an input tuple at the end of the execute method, see IBasicBolt which automates this.
execute
in interface IBolt
input
- The input tuple to be processed.public void cleanup()
IBolt
The one context where cleanup is guaranteed to be called is when a topology is killed when running Storm in local mode.
cleanup
in interface IBolt
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