org.apache.beam.sdk.coders

Class MapCoder<K,V>

java.lang.Object

org.apache.beam.sdk.coders.StandardCoder<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, Coder<Map<K,V>>

public class MapCoder<K,V>
extends StandardCoder<Map<K,V>>

A Coder for Maps that encodes them according to provided coders for keys and values.

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from interface org.apache.beam.sdk.coders.Coder

Coder.Context, Coder.NonDeterministicException

Method Summary

Modifier and Type	Method and Description
Map<K,V>	decode(InputStream inStream, Coder.Context context) Decodes a value of type T from the given input stream in the given context.
void	encode(Map<K,V> map, OutputStream outStream, Coder.Context context) Encodes the given value of type T onto the given output stream in the given context.
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, or returns null if this cannot be done or this is not a parameterized type.
static <K,V> List<Object>	getInstanceComponents(Map<K,V> exampleValue) Returns the key and value for an arbitrary element of this map, if it is non-empty, otherwise returns null.
Coder<K>	getKeyCoder()
Coder<V>	getValueCoder()
static <K,V> MapCoder<K,V>	of(Coder<K> keyCoder, Coder<V> valueCoder) Produces a MapCoder with the given keyCoder and valueCoder.
static MapCoder<?,?>	of(List<Coder<?>> components)
void	registerByteSizeObserver(Map<K,V> map, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer, Coder.Context context) Notifies the ElementByteSizeObserver about the byte size of the encoded value using this Coder.
void	verifyDeterministic() Throw Coder.NonDeterministicException if the coding is not deterministic.

Methods inherited from class org.apache.beam.sdk.coders.StandardCoder

asCloudObject, consistentWithEquals, equals, getAllowedEncodings, getComponents, getEncodedElementByteSize, getEncodingId, hashCode, isRegisterByteSizeObserverCheap, structuralValue, toString, verifyDeterministic, verifyDeterministic

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

of

public static <K,V> MapCoder<K,V> of(Coder<K> keyCoder,
                                     Coder<V> valueCoder)

Produces a MapCoder with the given keyCoder and valueCoder.

of

public static MapCoder<?,?> of(List<Coder<?>> components)

getInstanceComponents

public static <K,V> List<Object> getInstanceComponents(Map<K,V> exampleValue)

Returns the key and value for an arbitrary element of this map, if it is non-empty, otherwise returns null.

getKeyCoder

public Coder<K> getKeyCoder()

getValueCoder

public Coder<V> getValueCoder()

encode

public void encode(Map<K,V> map,
                   OutputStream outStream,
                   Coder.Context context)
            throws IOException,
                   CoderException

Description copied from interface: Coder

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 Map<K,V> decode(InputStream inStream,
                       Coder.Context context)
                throws IOException,
                       CoderException

Description copied from interface: Coder

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 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, or returns null if this cannot be done or this is not a parameterized type.

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.

Throws:

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.

Coder.NonDeterministicException - if this coder is not deterministic.

registerByteSizeObserver

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

Description copied from class: StandardCoder

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.

For StandardCoder subclasses, this notifies observer about the byte size of the encoded value using this coder as returned by StandardCoder.getEncodedElementByteSize(T, org.apache.beam.sdk.coders.Coder.Context).

Specified by:

registerByteSizeObserver in interface Coder<Map<K,V>>

Overrides:

registerByteSizeObserver in class StandardCoder<Map<K,V>>

Throws:

Exception