org.apache.uima.collection

## Interface CollectionProcessingEngine

-     public interface CollectionProcessingEngine

  A `CollectionProcessingEngine` (CPE) processes a collection of artifacts (for text analysis applications, this will be a collection of documents) and produces collection-level results.

  A CPE consists of a `CollectionReader`, zero or more `AnalysisEngine`s and zero or more `CasConsumer`s. The Collection Reader is responsible for reading artifacts from a collection and setting up the CAS. The AnalysisEngines analyze each CAS and the results are passed on to the CAS Consumers. CAS Consumers perform analysis over multiple CASes and generally produce collection-level results in some application-specific data structure.

  Processing is started by calling the `process()` method. Processing can be controlled via the`pause()`, `resume()`, and `stop()` methods.

  Listeners can register with the CPE by calling the `addStatusCallbackListener(StatusCallbackListener)` method. These listeners receive status callbacks during the processing. At any time, performance and progress reports are available from the `getPerformanceReport()` and `getProgress()` methods.

  A CPE implementation may choose to implement parallelization of the processing, but this is not a requirement of the architecture.

  Note that a CPE only supports processing one collection at a time. Attempting to start a new processing job while a previous processing job is running will result in an exception. Processing multiple collections simultaneously is done by instantiating and configuring multiple instances of the CPE.

  A `CollectionProcessingEngine` instance can be obtained by calling `UIMAFramework.produceCollectionProcessingEngine(CpeDescription)`.

- - ### Method Summary

    All Methods Instance Methods Abstract Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addStatusCallbackListener(StatusCallbackListener aListener)` Registers a listener to receive status callbacks.
    `CasProcessor[]` | `getCasProcessors()` Gets the `CasProcessors`s in this CPE, in the order in which they will be executed.
    `BaseCollectionReader` | `getCollectionReader()` Gets the Collection Reader for this CPE.
    `ProcessTrace` | `getPerformanceReport()` Gets a performance report for the processing that is currently occurring or has just completed.
    `Progress[]` | `getProgress()` Gets a progress report for the processing that is currently occurring or has just completed.
    `void` | `initialize(CpeDescription aCpeDescription, Map<String,Object> aAdditionalParams)` Initializes this CPE from a `cpeDescription` Applications do not need to call this method.
    `boolean` | `isPaused()` Determines whether this CPE's processing is currently paused.
    `boolean` | `isProcessing()` Determines whether this CPE is currently processing.
    `void` | `kill()` Kill CPM hard.
    `void` | `pause()` Pauses processing.
    `void` | `process()` Initiates processing of a collection.
    `void` | `removeStatusCallbackListener(StatusCallbackListener aListener)` Unregisters a status callback listener.
    `void` | `resume()` Resumes processing that has been paused.
    `void` | `stop()` Stops processing.

- - ### Method Detail

    - #### initialize

          void initialize(CpeDescription aCpeDescription,
                          Map<String,Object> aAdditionalParams)
                   throws ResourceInitializationException

      Initializes this CPE from a `cpeDescription` Applications do not need to call this method. It is called automatically by the framework and cannot be called a second time.
      Parameters:
        `aCpeDescription` - CPE description, generally parsed from an XML file
        `aAdditionalParams` - a Map containing additional parameters. May be `null` if there are no parameters. Each class that implements this interface can decide what additional parameters it supports.
      Throws:
        `ResourceInitializationException` - if a failure occurs during initialization.
        `UIMA_IllegalStateException` - if this method is called more than once on a single instance.

    - #### addStatusCallbackListener

          void addStatusCallbackListener(StatusCallbackListener aListener)

      Registers a listener to receive status callbacks.
      Parameters:
        `aListener` - the listener to add

    - #### removeStatusCallbackListener

          void removeStatusCallbackListener(StatusCallbackListener aListener)

      Unregisters a status callback listener.
      Parameters:
        `aListener` - the listener to remove

    - #### process

          void process()
                throws ResourceInitializationException

      Initiates processing of a collection. This method starts the processing in another thread and returns immediately. Status of the processing can be obtained by registering a listener with the `addStatusCallbackListener(StatusCallbackListener)` method.

      A CPE can only process one collection at a time. If this method is called while a previous processing request has not yet completed, a `UIMA_IllegalStateException` will result. To find out whether a CPE is free to begin another processing request, call the `isProcessing()` method.

      Throws:
        `ResourceInitializationException` - if an error occurs during initialization
        `UIMA_IllegalStateException` - if this CPE is currently processing

    - #### isProcessing

          boolean isProcessing()

      Determines whether this CPE is currently processing. This means that a processing request has been submitted and has not yet completed or been `stop()`ped. If processing is paused, this method will still return `true`.
      Returns:
        true if and only if this CPE is currently processing.

    - #### pause

          void pause()

      Pauses processing. Processing can later be resumed by calling the `resume()` method.
      Throws:
        `UIMA_IllegalStateException` - if no processing is currently occuring

    - #### isPaused

          boolean isPaused()

      Determines whether this CPE's processing is currently paused.
      Returns:
        true if and only if this CPE's processing is currently paused.

    - #### resume

          void resume()

      Resumes processing that has been paused.
      Throws:
        `UIMA_IllegalStateException` - if processing is not currently paused

    - #### stop

          void stop()

      Stops processing.
      Throws:
        `UIMA_IllegalStateException` - if no processing is currently occuring

    - #### getPerformanceReport

          ProcessTrace getPerformanceReport()

      Gets a performance report for the processing that is currently occurring or has just completed.
      Returns:
        an object containing performance statistics

    - #### getProgress

          Progress[] getProgress()

      Gets a progress report for the processing that is currently occurring or has just completed.
      Returns:
        an array of `Progress` objects, each of which represents the progress in a different set of units (for example number of entities or bytes)

    - #### getCollectionReader

          BaseCollectionReader getCollectionReader()

      Gets the Collection Reader for this CPE.
      Returns:
        the collection reader

    - #### getCasProcessors

          CasProcessor[] getCasProcessors()

      Gets the `CasProcessors`s in this CPE, in the order in which they will be executed.
      Returns:
        an array of `CasProcessor`s

    - #### kill

          void kill()

      Kill CPM hard.

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