org.apache.beam.sdk.transforms

Class DoFn<InputT,OutputT>

java.lang.Object

org.apache.beam.sdk.transforms.DoFn<InputT,OutputT>

Type Parameters:

InputT - the type of the (main) input elements

OutputT - the type of the (main) output elements

All Implemented Interfaces:

java.io.Serializable, HasDisplayData

Direct Known Subclasses:

BatchStatefulParDoOverrides.BatchStatefulDoFn, BeamAggregationTransforms.MergeAggregationRecord, BeamJoinTransforms.SideInputJoinDoFn, BeamSetOperatorsTransforms.SetOperatorFilteringDoFn, BeamSqlOutputToConsoleFn, DataflowRunner.StreamingPCollectionViewWriterFn, PubsubIO.Write.PubsubBoundedWriter, PubsubMessageToRow, ValueWithRecordId.StripIdsDoFn

public abstract class DoFn<InputT,OutputT>
extends java.lang.Object
implements java.io.Serializable, HasDisplayData

The argument to ParDo providing the code to use to process elements of the input PCollection.

See ParDo for more explanation, examples of use, and discussion of constraints on DoFns, including their serializability, lack of access to global shared mutable state, requirements for failure tolerance, and benefits of optimization.

DoFns can be tested by using TestPipeline. You can verify their functional correctness in a local test using the DirectRunner as well as running integration tests with your production runner of choice. Typically, you can generate the input data using Create.of(java.lang.Iterable<T>) or other transforms. However, if you need to test the behavior of DoFn.StartBundle and DoFn.FinishBundle with particular bundle boundaries, you can use TestStream.

Implementations must define a method annotated with DoFn.ProcessElement that satisfies the requirements described there. See the DoFn.ProcessElement for details.

Example usage:

  PCollection<String> lines = ... ;
  PCollection<String> words =
      lines.apply(ParDo.of(new DoFn<String, String>()) {
          @ProcessElement
          public void processElement( @Element String element, BoundedWindow window) {
            ...
          }}));
 

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	DoFn.BoundedPerElement Annotation on a splittable DoFn specifying that the DoFn performs a bounded amount of work per input element, so applying it to a bounded PCollection will produce also a bounded PCollection.
static interface	DoFn.Element Parameter annotation for the input element for a DoFn.ProcessElement method.
static interface	DoFn.FieldAccess Annotation for specifying specific fields that are accessed in a Schema PCollection.
static interface	DoFn.FinishBundle Annotation for the method to use to finish processing a batch of elements.
class	DoFn.FinishBundleContext Information accessible while within the DoFn.FinishBundle method.
static interface	DoFn.GetInitialRestriction Annotation for the method that maps an element to an initial restriction for a splittable DoFn.
static interface	DoFn.GetRestrictionCoder Annotation for the method that returns the coder to use for the restriction of a splittable DoFn.
static interface	DoFn.MultiOutputReceiver Receives tagged output for a multi-output function.
static interface	DoFn.NewTracker Annotation for the method that creates a new RestrictionTracker for the restriction of a splittable DoFn.
static interface	DoFn.OnTimer Annotation for registering a callback for a timer.
class	DoFn.OnTimerContext Information accessible when running a DoFn.OnTimer method.
static interface	DoFn.OnWindowExpiration Annotation for the method to use for performing actions on window expiration.
static interface	DoFn.OutputReceiver<T> Receives values of the given type.
class	DoFn.ProcessContext Information accessible when running a DoFn.ProcessElement method.
static class	DoFn.ProcessContinuation When used as a return value of DoFn.ProcessElement, indicates whether there is more work to be done for the current element.
static interface	DoFn.ProcessElement Annotation for the method to use for processing elements.
static interface	DoFn.RequiresStableInput Experimental - no backwards compatibility guarantees.
static interface	DoFn.Setup Annotation for the method to use to prepare an instance for processing bundles of elements.
static interface	DoFn.SplitRestriction Annotation for the method that splits restriction of a splittable DoFn into multiple parts to be processed in parallel.
static interface	DoFn.StartBundle Annotation for the method to use to prepare an instance for processing a batch of elements.
class	DoFn.StartBundleContext Information accessible while within the DoFn.StartBundle method.
static interface	DoFn.StateId Annotation for declaring and dereferencing state cells.
static interface	DoFn.Teardown Annotation for the method to use to clean up this instance before it is discarded.
static interface	DoFn.TimerId Annotation for declaring and dereferencing timers.
static interface	DoFn.Timestamp Parameter annotation for the input element timestamp for a DoFn.ProcessElement method.
static interface	DoFn.UnboundedPerElement Annotation on a splittable DoFn specifying that the DoFn performs an unbounded amount of work per input element, so applying it to a bounded PCollection will produce an unbounded PCollection.
class	DoFn.WindowedContext Information accessible to all methods in this DoFn where the context is in some window.

Constructor Summary

Constructors

Constructor and Description
DoFn()

Method Summary

Modifier and Type	Method and Description
Duration	getAllowedTimestampSkew() Deprecated. This method permits a DoFn to emit elements behind the watermark. These elements are considered late, and if behind the allowed lateness of a downstream PCollection may be silently dropped. See https://issues.apache.org/jira/browse/BEAM-644 for details on a replacement.
TypeDescriptor<InputT>	getInputTypeDescriptor() Returns a TypeDescriptor capturing what is known statically about the input type of this DoFn instance's most-derived class.
TypeDescriptor<OutputT>	getOutputTypeDescriptor() Returns a TypeDescriptor capturing what is known statically about the output type of this DoFn instance's most-derived class.
void	populateDisplayData(DisplayData.Builder builder) Register display data for the given transform or component.
void	prepareForProcessing() Deprecated. use DoFn.Setup or DoFn.StartBundle instead. This method will be removed in a future release.

Methods inherited from class java.lang.Object

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

Constructor Detail

DoFn

public DoFn()

Method Detail

getAllowedTimestampSkew

@Deprecated
public Duration getAllowedTimestampSkew()

Deprecated. This method permits a DoFn to emit elements behind the watermark. These elements are considered late, and if behind the allowed lateness of a downstream PCollection may be silently dropped. See https://issues.apache.org/jira/browse/BEAM-644 for details on a replacement.

Returns the allowed timestamp skew duration, which is the maximum duration that timestamps can be shifted backward in DoFn.WindowedContext.outputWithTimestamp(OutputT, org.joda.time.Instant).

The default value is Duration.ZERO, in which case timestamps can only be shifted forward to future. For infinite skew, return Duration.millis(Long.MAX_VALUE).

getInputTypeDescriptor

public TypeDescriptor<InputT> getInputTypeDescriptor()

Returns a TypeDescriptor capturing what is known statically about the input type of this DoFn instance's most-derived class.

See getOutputTypeDescriptor() for more discussion.

getOutputTypeDescriptor

public TypeDescriptor<OutputT> getOutputTypeDescriptor()

Returns a TypeDescriptor capturing what is known statically about the output type of this DoFn instance's most-derived class.

In the normal case of a concrete DoFn subclass with no generic type parameters of its own (including anonymous inner classes), this will be a complete non-generic type, which is good for choosing a default output Coder<O> for the output PCollection<O>.

prepareForProcessing

@Deprecated
public final void prepareForProcessing()

Deprecated. use DoFn.Setup or DoFn.StartBundle instead. This method will be removed in a future release.

Finalize the DoFn construction to prepare for processing. This method should be called by runners before any processing methods.

populateDisplayData

public void populateDisplayData(DisplayData.Builder builder)

Register display data for the given transform or component.

populateDisplayData(DisplayData.Builder) is invoked by Pipeline runners to collect display data via DisplayData.from(HasDisplayData). Implementations may call super.populateDisplayData(builder) in order to register display data in the current namespace, but should otherwise use subcomponent.populateDisplayData(builder) to use the namespace of the subcomponent.

By default, does not register any display data. Implementors may override this method to provide their own display data.

Specified by:

populateDisplayData in interface HasDisplayData

Parameters:

builder - The builder to populate with display data.

See Also:

HasDisplayData