Package org.apache.beam.sdk.coders

Class IterableLikeCoder<T,​IterableT extends java.lang.Iterable<T>>

  • Type Parameters:
    T - the type of the elements of the Iterables being transcoded
    IterableT - the type of the Iterables being transcoded
    All Implemented Interfaces:
    java.io.Serializable
    Direct Known Subclasses:
    CollectionCoder, DequeCoder, IterableCoder, ListCoder, SetCoder
    public abstract class IterableLikeCoder<T,​IterableT extends java.lang.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:
    Serialized Form

    • Constructor Detail

      • IterableLikeCoder

        protected IterableLikeCoder​(Coder<T> elementCoder,
                            java.lang.String iterableName)

    • Method Detail

      • getElemCoder

        public Coder<T> getElemCoder()

      • decodeToIterable

        protected abstract IterableT decodeToIterable​(java.util.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​(java.util.List<T> decodedElements,
                                     long terminatorValue,
                                     java.io.InputStream in)
                              throws java.io.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:
        java.io.IOException

      • encode

        public void encode​(IterableT iterable,
                   java.io.OutputStream outStream)
            throws java.io.IOException,
                   CoderException
        Description copied from class: Coder
        Encodes the given value of type T onto the given output stream.
        Specified by:
        encode in class Coder<IterableT extends java.lang.Iterable<T>>
        Throws:
        java.io.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​(java.io.InputStream inStream)
                 throws java.io.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.
        Specified by:
        decode in class Coder<IterableT extends java.lang.Iterable<T>>
        Throws:
        java.io.IOException - if reading from the InputStream fails for some reason
        CoderException - if the value could not be decoded for some reason

      • getCoderArguments

        public java.util.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 java.lang.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 java.lang.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.

      • registerByteSizeObserver

        public void registerByteSizeObserver​(IterableT iterable,
                                     ElementByteSizeObserver observer)
                              throws java.lang.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 java.lang.Iterable<T>>
        Throws:
        java.lang.Exception