Package org.apache.beam.sdk.coders

Class Coder<T>

java.lang.Object
org.apache.beam.sdk.coders.Coder<T>
Type Parameters:
T - the type of values being encoded and decoded
All Implemented Interfaces:
Serializable
Direct Known Subclasses:
CustomCoder, StructuredCoder, ZstdCoder
public abstract class Coder<T> extends Object implements Serializable
A Coder<T> defines how to encode and decode values of type T into byte streams.

Coder instances are serialized during job creation and deserialized before use. This will generally be performed by serializing the object via Java Serialization.

Coder classes for compound types are often composed from coder classes for types contains therein. The composition of Coder instances into a coder for the compound class is the subject of the CoderProvider type, which enables automatic generic composition of Coder classes within the CoderRegistry. See CoderProvider and CoderRegistry for more information about how coders are inferred.

All methods of a Coder are required to be thread safe.

See Also:

  • Constructor Details

    • Coder

      public Coder()

  • Method Details

    • encode

      public abstract void encode(T value, OutputStream outStream) throws CoderException, IOException
      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.
      Throws:
      IOException - if writing to the OutputStream fails for some reason
      CoderException - if the value could not be encoded for some reason

    • encode

      @Deprecated public void encode(T value, OutputStream outStream, Coder.Context context) throws CoderException, IOException
      Deprecated.
      only implement and call encode(Object value, OutputStream)
      Encodes the given value of type T onto the given output stream in the given context.
      Throws:
      IOException - if writing to the OutputStream fails for some reason
      CoderException - if the value could not be encoded for some reason

    • decode

      public abstract T decode(InputStream inStream) throws CoderException, IOException
      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.
      Throws:
      IOException - if reading from the InputStream fails for some reason
      CoderException - if the value could not be decoded for some reason

    • decode

      @Deprecated public T decode(InputStream inStream, Coder.Context context) throws CoderException, IOException
      Deprecated.
      only implement and call decode(InputStream)
      Decodes a value of type T from the given input stream in the given context. Returns the decoded value.
      Throws:
      IOException - if reading from the InputStream fails for some reason
      CoderException - if the value could not be decoded for some reason

    • getCoderArguments

      public abstract List<? extends Coder<?>> getCoderArguments()
      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.

    • verifyDeterministic

      public abstract 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.
      Throws:
      Coder.NonDeterministicException - if this coder is not deterministic.

    • verifyDeterministic

      public static void verifyDeterministic(Coder<?> target, String message, Iterable<Coder<?>> coders) throws Coder.NonDeterministicException
      Verifies all of the provided coders are deterministic. If any are not, throws a Coder.NonDeterministicException for the target Coder.
      Throws:
      Coder.NonDeterministicException

    • getEncodedElementByteSizeUsingCoder

      public static <T> long getEncodedElementByteSizeUsingCoder(Coder<T> target, T value) throws Exception
      Throws:
      Exception

    • verifyDeterministic

      public static void verifyDeterministic(Coder<?> target, String message, Coder<?>... coders) throws Coder.NonDeterministicException
      Verifies all of the provided coders are deterministic. If any are not, throws a Coder.NonDeterministicException for the target Coder.
      Throws:
      Coder.NonDeterministicException

    • consistentWithEquals

      public boolean consistentWithEquals()
      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.

    • structuralValue

      public Object structuralValue(T value)
      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 consistentWithEquals().

      By default, if this coder is 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.

    • isRegisterByteSizeObserverCheap

      public boolean isRegisterByteSizeObserverCheap(T value)
      Returns whether 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 registerByteSizeObserver(T, org.apache.beam.sdk.util.common.ElementByteSizeObserver) implementation invokes getEncodedElementByteSize(T) which requires re-encoding an element unless it is overridden. This is considered expensive.

    • registerByteSizeObserver

      public void registerByteSizeObserver(T value, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer) throws Exception
      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 getEncodedElementByteSize(T).

      Throws:
      Exception

    • getEncodedElementByteSize

      protected long getEncodedElementByteSize(T value) throws Exception
      Returns the size in bytes of the encoded value using this coder.
      Throws:
      Exception

    • getEncodedTypeDescriptor

      public TypeDescriptor<T> getEncodedTypeDescriptor()
      Returns the TypeDescriptor for the type encoded.