Package org.apache.beam.sdk.coders

Class IterableLikeCoder<T,IterableT extends Iterable<T>>

java.lang.Object
org.apache.beam.sdk.coders.Coder<IterableT>
org.apache.beam.sdk.coders.StructuredCoder<IterableT>
org.apache.beam.sdk.coders.IterableLikeCoder<T,IterableT>
Type Parameters:
T - the type of the elements of the Iterables being transcoded
IterableT - the type of the Iterables being transcoded
All Implemented Interfaces:
Serializable
Direct Known Subclasses:
CollectionCoder, DequeCoder, IterableCoder, ListCoder, SetCoder
public abstract class IterableLikeCoder<T,IterableT extends Iterable<T>> extends StructuredCoder<IterableT>
An abstract base class with functionality for assembling a Coder for a class that implements Iterable.

To complete a subclass, implement the decodeToIterable(java.util.List<T>) method. This superclass will decode the elements in the input stream into a List and then pass them to that method to be converted into the appropriate iterable type. Note that this means the input iterables must fit into memory.

The format of this coder is as follows:

  • If the input Iterable has a known and finite size, then the size is written to the output stream in big endian format, followed by all of the encoded elements.
  • If the input Iterable is not known to have a finite size, then each element of the input is preceded by true encoded as a byte (indicating "more data") followed by the encoded element, and terminated by false encoded as a byte.
See Also:

  • Constructor Details

    • IterableLikeCoder

      protected IterableLikeCoder(Coder<T> elementCoder, String iterableName)

  • Method Details

    • getElemCoder

      public Coder<T> getElemCoder()

    • decodeToIterable

      protected abstract IterableT decodeToIterable(List<T> decodedElements)
      Builds an instance of IterableT, this coder's associated Iterable-like subtype, from a list of decoded elements.

      Override decodeToIterable(List, long, InputStream) if you need access to the terminator value and the InputStream.

    • decodeToIterable

      protected IterableT decodeToIterable(List<T> decodedElements, long terminatorValue, InputStream in) throws IOException
      Builds an instance of IterableT, this coder's associated Iterable-like subtype, from a list of decoded elements with the InputStream at the position where this coder detected the end of the stream.
      Throws:
      IOException

    • encode

      public void encode(IterableT iterable, OutputStream outStream) throws IOException, CoderException
      Description copied from class: Coder
      Encodes the given value of type T onto the given output stream. Multiple elements can be encoded next to each other on the output stream, each coder should encode information to know how many bytes to read when decoding. A common approach is to prefix the encoding with the element's encoded length.
      Specified by:
      encode in class Coder<IterableT extends Iterable<T>>
      Throws:
      IOException - if writing to the OutputStream fails for some reason
      CoderException - if the value could not be encoded for some reason

    • decode

      public IterableT decode(InputStream inStream) throws IOException, CoderException
      Description copied from class: Coder
      Decodes a value of type T from the given input stream in the given context. Returns the decoded value. Multiple elements can be encoded next to each other on the input stream, each coder should encode information to know how many bytes to read when decoding. A common approach is to prefix the encoding with the element's encoded length.
      Specified by:
      decode in class Coder<IterableT extends Iterable<T>>
      Throws:
      IOException - if reading from the InputStream fails for some reason
      CoderException - if the value could not be decoded for some reason

    • getCoderArguments

      public List<? extends Coder<?>> getCoderArguments()
      Description copied from class: Coder
      If this is a Coder for a parameterized type, returns the list of Coders being used for each of the parameters in the same order they appear within the parameterized type's type signature. If this cannot be done, or this Coder does not encode/decode a parameterized type, returns the empty list.
      Specified by:
      getCoderArguments in class Coder<IterableT extends Iterable<T>>

    • verifyDeterministic

      public void verifyDeterministic() throws Coder.NonDeterministicException
      Throw Coder.NonDeterministicException if the coding is not deterministic.

      In order for a Coder to be considered deterministic, the following must be true:

      • two values that compare as equal (via Object.equals() or Comparable.compareTo(), if supported) have the same encoding.
      • the Coder always produces a canonical encoding, which is the same for an instance of an object even if produced on different computers at different times.
      Specified by:
      verifyDeterministic in class Coder<IterableT extends Iterable<T>>
      Throws:
      Coder.NonDeterministicException - always. Encoding is not deterministic for the general Iterable case, as it depends upon the type of iterable. This may allow two objects to compare as equal while the encoding differs.

    • isRegisterByteSizeObserverCheap

      public boolean isRegisterByteSizeObserverCheap(IterableT iterable)
      Returns whether Coder.registerByteSizeObserver(T, org.apache.beam.sdk.util.common.ElementByteSizeObserver) cheap enough to call for every element, that is, if this Coder can calculate the byte size of the element to be coded in roughly constant time (or lazily).

      Not intended to be called by user code, but instead by PipelineRunner implementations.

      By default, returns false. The default Coder.registerByteSizeObserver(T, org.apache.beam.sdk.util.common.ElementByteSizeObserver) implementation invokes Coder.getEncodedElementByteSize(T) which requires re-encoding an element unless it is overridden. This is considered expensive.

      Overrides:
      isRegisterByteSizeObserverCheap in class Coder<IterableT extends Iterable<T>>
      Returns:
      true if the iterable is of a known class that supports lazy counting of byte size, since that requires minimal extra computation.

    • registerByteSizeObserver

      public void registerByteSizeObserver(IterableT iterable, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer) throws Exception
      Description copied from class: Coder
      Notifies the ElementByteSizeObserver about the byte size of the encoded value using this Coder.

      Not intended to be called by user code, but instead by PipelineRunner implementations.

      By default, this notifies observer about the byte size of the encoded value using this coder as returned by Coder.getEncodedElementByteSize(T).

      Overrides:
      registerByteSizeObserver in class Coder<IterableT extends Iterable<T>>
      Throws:
      Exception