org.apache.beam.sdk.coders

Class NullableCoder<T>

java.lang.Object

org.apache.beam.sdk.coders.StandardCoder<T>

org.apache.beam.sdk.coders.NullableCoder<T>

Type Parameters:

T - the type of the values being transcoded

All Implemented Interfaces:

Serializable, Coder<T>

public class NullableCoder<T>
extends StandardCoder<T>

A NullableCoder encodes nullable values of type T using a nested Coder<T> that does not tolerate null values. NullableCoder uses exactly 1 byte per entry to indicate whether the value is null, then adds the encoding of the inner coder for non-null 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
boolean	consistentWithEquals() NullableCoder is consistent with equals if the nested Coder is.
T	decode(InputStream inStream, Coder.Context context) Decodes a value of type T from the given input stream in the given context.
void	encode(T value, OutputStream outStream, Coder.Context context) Encodes the given value of type T onto the given output stream in the given context.
List<Coder<T>>	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.
protected long	getEncodedElementByteSize(T value, Coder.Context context) Overridden to short-circuit the default StandardCoder behavior of encoding and counting the bytes.
boolean	isRegisterByteSizeObserverCheap(T value, Coder.Context context) NullableCoder is cheap if valueCoder is cheap.
static <T> NullableCoder<T>	of(Coder<T> valueCoder)
static NullableCoder<?>	of(List<Coder<?>> components)
void	registerByteSizeObserver(T value, org.apache.beam.sdk.util.common.ElementByteSizeObserver observer, Coder.Context context) Overridden to short-circuit the default StandardCoder behavior of encoding and counting the bytes.
Object	structuralValue(T value) Returns an object with an Object.equals() method that represents structural equality on the argument.
void	verifyDeterministic() NullableCoder is deterministic if the nested Coder is.

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

asCloudObject, equals, getAllowedEncodings, getComponents, getEncodingId, hashCode, toString, verifyDeterministic, verifyDeterministic

Methods inherited from class java.lang.Object

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

Method Detail

of

public static <T> NullableCoder<T> of(Coder<T> valueCoder)

of

public static NullableCoder<?> of(List<Coder<?>> components)

encode

public void encode(@Nullable
                   T value,
                   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

@Nullable
public T 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<Coder<T>> getCoderArguments()

Description copied from interface: Coder

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.

verifyDeterministic

public void verifyDeterministic()
                         throws Coder.NonDeterministicException

NullableCoder 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.

Throws:

Coder.NonDeterministicException - if this coder is not deterministic.

consistentWithEquals

public boolean consistentWithEquals()

NullableCoder 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.

Specified by:

consistentWithEquals in interface Coder<T>

Overrides:

consistentWithEquals in class StandardCoder<T>

Returns:

false for StandardCoder unless overridden.

structuralValue

public Object structuralValue(@Nullable
                              T value)
                       throws Exception

Description copied from interface: 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(@code 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().

Specified by:

structuralValue in interface Coder<T>

Overrides:

structuralValue in class StandardCoder<T>

Throws:

Exception

registerByteSizeObserver

public void registerByteSizeObserver(@Nullable
                                     T value,
                                     org.apache.beam.sdk.util.common.ElementByteSizeObserver observer,
                                     Coder.Context context)
                              throws Exception

Overridden to short-circuit the default StandardCoder behavior of encoding and counting the bytes. The size is known (1 byte) when value is null, otherwise the size is 1 byte plus the size of nested Coder's encoding of value. 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<T>

Overrides:

registerByteSizeObserver in class StandardCoder<T>

Throws:

Exception

getEncodedElementByteSize

protected long getEncodedElementByteSize(@Nullable
                                         T value,
                                         Coder.Context context)
                                  throws Exception

Overridden to short-circuit the default StandardCoder behavior of encoding and counting the bytes. The size is known (1 byte) when value is null, otherwise the size is 1 byte plus the size of nested Coder's encoding of value. Returns the size in bytes of the encoded value using this coder.

Overrides:

getEncodedElementByteSize in class StandardCoder<T>

Throws:

Exception

isRegisterByteSizeObserverCheap

public boolean isRegisterByteSizeObserverCheap(@Nullable
                                               T value,
                                               Coder.Context context)

NullableCoder is cheap if valueCoder is cheap. Returns whether Coder.registerByteSizeObserver(T, org.apache.beam.sdk.util.common.ElementByteSizeObserver, org.apache.beam.sdk.coders.Coder.Context) 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.

Specified by:

isRegisterByteSizeObserverCheap in interface Coder<T>

Overrides:

isRegisterByteSizeObserverCheap in class StandardCoder<T>

Returns:

false unless it is overridden. StandardCoder.registerByteSizeObserver(T, org.apache.beam.sdk.util.common.ElementByteSizeObserver, org.apache.beam.sdk.coders.Coder.Context) invokes StandardCoder.getEncodedElementByteSize(T, org.apache.beam.sdk.coders.Coder.Context) which requires re-encoding an element unless it is overridden. This is considered expensive.