Package org.apache.beam.sdk.coders

Class OptionalCoder<T>

java.lang.Object
org.apache.beam.sdk.coders.Coder<Optional<T>>
org.apache.beam.sdk.coders.StructuredCoder<Optional<T>>
org.apache.beam.sdk.coders.OptionalCoder<T>
Type Parameters:
T - the type of the values being transcoded
All Implemented Interfaces:
Serializable
public class OptionalCoder<T> extends StructuredCoder<Optional<T>>
A OptionalCoder encodes optional values of type T using a nested Coder<T>. OptionalCoder uses exactly 1 byte per entry to indicate whether the value is empty, then adds the encoding of the inner coder for non-empty values.
See Also:

  • Method Details

    • of

      public static <T> OptionalCoder<T> of(Coder<T> valueCoder)

    • getValueCoder

      public Coder<T> getValueCoder()
      Returns the inner Coder wrapped by this OptionalCoder instance.

    • encode

      public void encode(Optional<T> value, 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<Optional<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 Optional<T> 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<Optional<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<Coder<T>> 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<Optional<T>>

    • verifyDeterministic

      public void verifyDeterministic() throws Coder.NonDeterministicException
      OptionalCoder is deterministic if the nested Coder is.

      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<Optional<T>>
      Throws:
      Coder.NonDeterministicException - if this coder is not deterministic.

    • consistentWithEquals

      public boolean consistentWithEquals()
      OptionalCoder is consistent with equals if the nested Coder is.

      Returns true if this Coder is injective with respect to Object.equals(java.lang.Object).

      Whenever the encoded bytes of two values are equal, then the original values are equal according to Objects.equals(). Note that this is well-defined for null.

      This condition is most notably false for arrays. More generally, this condition is false whenever equals() compares object identity, rather than performing a semantic/structural comparison.

      By default, returns false.

      Overrides:
      consistentWithEquals in class Coder<Optional<T>>

    • structuralValue

      public Object structuralValue(Optional<T> value)
      Description copied from class: Coder
      Returns an object with an Object.equals() method that represents structural equality on the argument.

      For any two values x and y of type T, if their encoded bytes are the same, then it must be the case that structuralValue(x).equals(structuralValue(y)).

      Most notably:

      • The structural value for an array coder should perform a structural comparison of the contents of the arrays, rather than the default behavior of comparing according to object identity.
      • The structural value for a coder accepting null should be a proper object with an equals() method, even if the input value is null.

      See also Coder.consistentWithEquals().

      By default, if this coder is Coder.consistentWithEquals(), and the value is not null, returns the provided object. Otherwise, encodes the value into a byte[], and returns an object that performs array equality on the encoded bytes.

      Overrides:
      structuralValue in class Coder<Optional<T>>

    • registerByteSizeObserver

      public void registerByteSizeObserver(Optional<T> value, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer) throws Exception
      Overridden to short-circuit the default StructuredCoder behavior of encoding and counting the bytes. The size is known (1 byte) when value is null, otherwise the size is 1 byte plus the size of nested Coder's encoding of value.

      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<Optional<T>>
      Throws:
      Exception

    • getEncodedElementByteSize

      protected long getEncodedElementByteSize(Optional<T> value) throws Exception
      Overridden to short-circuit the default StructuredCoder behavior of encoding and counting the bytes. The size is known (1 byte) when value is null, otherwise the size is 1 byte plus the size of nested Coder's encoding of value.

      Returns the size in bytes of the encoded value using this coder.

      Overrides:
      getEncodedElementByteSize in class Coder<Optional<T>>
      Throws:
      Exception

    • isRegisterByteSizeObserverCheap

      public boolean isRegisterByteSizeObserverCheap(Optional<T> value)
      OptionalCoder is cheap if valueCoder is cheap.

      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<Optional<T>>

    • getEncodedTypeDescriptor

      public TypeDescriptor<Optional<T>> getEncodedTypeDescriptor()
      Description copied from class: Coder
      Returns the TypeDescriptor for the type encoded.
      Overrides:
      getEncodedTypeDescriptor in class Coder<Optional<T>>