Package org.apache.beam.sdk.coders

Class LengthPrefixCoder<T>

  • Type Parameters:
    T - the type of the values being transcoded
    All Implemented Interfaces:
    java.io.Serializable
    public class LengthPrefixCoder<T>
extends StructuredCoder<T>
    A Coder which is able to take any existing coder and wrap it such that it is only invoked in the outer context. The data representing the element is prefixed with a length using a variable integer encoding.
    See Also:
    Serialized Form

    • Method Detail

      • encode

        public void encode​(T value,
                   java.io.OutputStream outStream)
            throws CoderException,
                   java.io.IOException
        Description copied from class: Coder
        Encodes the given value of type T onto the given output stream.
        Specified by:
        encode in class Coder<T>
        Throws:
        CoderException - if the value could not be encoded for some reason
        java.io.IOException - if writing to the OutputStream fails for some reason

      • decode

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

      • getValueCoder

        public Coder<T> getValueCoder()
        Gets the value coder that will be prefixed by the length.

      • verifyDeterministic

        public void verifyDeterministic()
                         throws Coder.NonDeterministicException
        LengthPrefixCoder 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<T>
        Throws:
        Coder.NonDeterministicException - if this coder is not deterministic.

      • consistentWithEquals

        public boolean consistentWithEquals()
        LengthPrefixCoder 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<T>

      • getEncodedElementByteSize

        protected long getEncodedElementByteSize​(T value)
                                  throws java.lang.Exception
        Overridden to short-circuit the default StructuredCoder behavior of encoding and counting the bytes. The size is known to be the size of the value plus the number of bytes required to prefix the length.

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

        Overrides:
        getEncodedElementByteSize in class Coder<T>
        Throws:
        java.lang.Exception