Package org.apache.beam.sdk.coders

Class Coder<T>

  • Type Parameters:
    T - the type of values being encoded and decoded
    All Implemented Interfaces:
    java.io.Serializable
    Direct Known Subclasses:
    CustomCoder, StructuredCoder, ZstdCoder
    public abstract class Coder<T>
extends java.lang.Object
implements java.io.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:
    Serialized Form

    • Constructor Detail

      • Coder

        public Coder()

    • Method Detail

      • encode

        public abstract void encode​(T value,
                            java.io.OutputStream outStream)
                     throws CoderException,
                            java.io.IOException
        Encodes the given value of type T onto the given output stream.
        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 abstract T decode​(java.io.InputStream inStream)
                  throws CoderException,
                         java.io.IOException
        Decodes a value of type T from the given input stream in the given context. Returns the decoded value.
        Throws:
        java.io.IOException - if reading from the InputStream fails for some reason
        CoderException - if the value could not be decoded for some reason

      • decode

        @Deprecated
@Experimental(CODER_CONTEXT)
public T decode​(java.io.InputStream inStream,
                Coder.Context context)
         throws CoderException,
                java.io.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:
        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 abstract java.util.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.

      • 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 java.lang.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.

      • registerByteSizeObserver

        public void registerByteSizeObserver​(T value,
                                     ElementByteSizeObserver observer)
                              throws java.lang.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:
        java.lang.Exception

      • getEncodedElementByteSize

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