Package org.apache.beam.sdk.coders

Class MapCoder<K,V>

java.lang.Object
org.apache.beam.sdk.coders.Coder<Map<K,V>>
org.apache.beam.sdk.coders.StructuredCoder<Map<K,V>>
org.apache.beam.sdk.coders.MapCoder<K,V>
Type Parameters:
K - the type of the keys of the KVs being transcoded
V - the type of the values of the KVs being transcoded
All Implemented Interfaces:
Serializable
public class MapCoder<K,V> extends StructuredCoder<Map<K,V>>
A Coder for Maps that encodes them according to provided coders for keys and values.
See Also:

  • Method Details

    • of

      public static <K, V> MapCoder<K,V> of(Coder<K> keyCoder, Coder<V> valueCoder)
      Produces a MapCoder with the given keyCoder and valueCoder.

    • getKeyCoder

      public Coder<K> getKeyCoder()

    • getValueCoder

      public Coder<V> getValueCoder()

    • encode

      public void encode(Map<K,V> map, 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<Map<K,V>>
      Throws:
      IOException - if writing to the OutputStream fails for some reason
      CoderException - if the value could not be encoded for some reason

    • encode

      public void encode(Map<K,V> map, OutputStream outStream, Coder.Context context) throws IOException, CoderException
      Description copied from class: Coder
      Encodes the given value of type T onto the given output stream in the given context.
      Overrides:
      encode in class Coder<Map<K,V>>
      Throws:
      IOException - if writing to the OutputStream fails for some reason
      CoderException - if the value could not be encoded for some reason

    • decode

      public Map<K,V> 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<Map<K,V>>
      Throws:
      IOException - if reading from the InputStream fails for some reason
      CoderException - if the value could not be decoded for some reason

    • decode

      public Map<K,V> decode(InputStream inStream, Coder.Context context) 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.
      Overrides:
      decode in class Coder<Map<K,V>>
      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<? 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.
      Specified by:
      getCoderArguments in class Coder<Map<K,V>>
      Returns:
      a List containing the key coder at index 0 at the and value coder at index 1.

    • 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<Map<K,V>>
      Throws:
      Coder.NonDeterministicException - always. Not all maps have a deterministic encoding. For example, HashMap comparison does not depend on element order, so two HashMap instances may be equal but produce different encodings.

    • consistentWithEquals

      public boolean consistentWithEquals()
      Description copied from class: Coder
      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<Map<K,V>>

    • structuralValue

      public Object structuralValue(Map<K,V> 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<Map<K,V>>

    • registerByteSizeObserver

      public void registerByteSizeObserver(Map<K,V> map, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer) throws 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<Map<K,V>>
      Throws:
      Exception

    • getEncodedTypeDescriptor

      public TypeDescriptor<Map<K,V>> getEncodedTypeDescriptor()
      Description copied from class: Coder
      Returns the TypeDescriptor for the type encoded.
      Overrides:
      getEncodedTypeDescriptor in class Coder<Map<K,V>>