cascading.tap
Class SinkTap<Config,Output>

java.lang.Object
  cascading.tap.Tap<Config,Void,Output>
      cascading.tap.SinkTap<Config,Output>

All Implemented Interfaces:

FlowElement, Traceable, Serializable

Direct Known Subclasses:

BaseTemplateTap, MultiSinkTap

public abstract class SinkTap<Config,Output>
extends Tap<Config,Void,Output>

Class SinkTap is an optional base class for sink only Taps.

Some Tap instances may only be sinks (as opposed to being a source). These types may subclass SinkTap for convenience or set isSource() to false in a custom Tap sub-class.

See Also:

Serialized Form

Constructor Summary

protected	SinkTap()
protected	SinkTap(Scheme<Config,?,Output,?,?> scheme)
protected	SinkTap(Scheme<Config,?,Output,?,?> scheme, SinkMode sinkMode)

Method Summary

Fields	getSourceFields() Method getSourceFields returns the sourceFields of this Tap object.
boolean	isSource() Method isSource returns true if this Tap instance can be used as a source.
TupleEntryIterator	openForRead(FlowProcess<Config> flowProcess, Void input) Method openForRead opens the resource represented by this Tap instance for reading.
boolean	prepareResourceForRead(Config conf) Method prepareResourceForRead allows the underlying resource to be notified when reading will begin.
void	sourceConfInit(FlowProcess<Config> flowProcess, Config conf) Method sourceConfInit initializes this instance as a source.

Methods inherited from class cascading.tap.Tap

commitResource, createResource, createResource, deleteResource, deleteResource, equals, flowConfInit, getConfigDef, getFullIdentifier, getFullIdentifier, getIdentifier, getModifiedTime, getModifiedTime, getScheme, getSinkFields, getSinkMode, getStepConfigDef, getTrace, hasConfigDef, hashCode, hasStepConfigDef, id, isEquivalentTo, isKeep, isReplace, isSink, isTemporary, isUpdate, openForRead, openForWrite, openForWrite, outgoingScopeFor, prepareResourceForWrite, presentSinkFields, presentSourceFields, resolveIncomingOperationArgumentFields, resolveIncomingOperationPassThroughFields, resourceExists, resourceExists, retrieveSinkFields, retrieveSourceFields, rollbackResource, setScheme, sinkConfInit, taps, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

SinkTap

protected SinkTap()

SinkTap

protected SinkTap(Scheme<Config,?,Output,?,?> scheme)

SinkTap

protected SinkTap(Scheme<Config,?,Output,?,?> scheme,
                  SinkMode sinkMode)

Method Detail

getSourceFields

public Fields getSourceFields()

Description copied from class: Tap

Method getSourceFields returns the sourceFields of this Tap object.

Overrides:

getSourceFields in class Tap<Config,Void,Output>

Returns:

the sourceFields (type Fields) of this Tap object.

prepareResourceForRead

public boolean prepareResourceForRead(Config conf)
                               throws IOException

Description copied from class: Tap

Method prepareResourceForRead allows the underlying resource to be notified when reading will begin.

This method will be called client side so that any remote or external resources can be initialized.

If this method returns false, an exception will be thrown halting the current Flow.

In most cases, resource initialization should happen in the Tap.openForRead(FlowProcess, Object) method.

This allows for initialization of cluster side resources, like a JDBC driver used to read data from a database, that cannot be passed client to cluster.

Overrides:

prepareResourceForRead in class Tap<Config,Void,Output>

Parameters:

conf - of type Config

Returns:

returns true if successful

Throws:

IOException

isSource

public boolean isSource()

Description copied from class: Tap

Method isSource returns true if this Tap instance can be used as a source.

Overrides:

isSource in class Tap<Config,Void,Output>

Returns:

boolean

sourceConfInit

public void sourceConfInit(FlowProcess<Config> flowProcess,
                           Config conf)

Description copied from class: Tap

Method sourceConfInit initializes this instance as a source.

This method maybe called more than once if this Tap instance is used outside the scope of a Flow instance or if it participates in multiple times in a given Flow or across different Flows in a Cascade.

In the context of a Flow, it will be called after FlowListener.onStarting(cascading.flow.Flow)

Note that no resources or services should be modified by this method.

Overrides:

sourceConfInit in class Tap<Config,Void,Output>

Parameters:

flowProcess - of type FlowProcess

conf - of type Config

openForRead

public TupleEntryIterator openForRead(FlowProcess<Config> flowProcess,
                                      Void input)
                               throws IOException

Description copied from class: Tap

Method openForRead opens the resource represented by this Tap instance for reading.

input value may be null, if so, sub-classes must inquire with the underlying Scheme via Scheme.sourceConfInit(cascading.flow.FlowProcess, Tap, Object) to get the proper input type and instantiate it before calling super.openForRead().

Note the returned iterator will return the same instance of TupleEntry on every call, thus a copy must be made of either the TupleEntry or the underlying Tuple instance if they are to be stored in a Collection.

Specified by:

openForRead in class Tap<Config,Void,Output>

Parameters:

flowProcess - of type FlowProcess

input - of type Input

Returns:

TupleEntryIterator

Throws:

IOException - when the resource cannot be opened