com.google.cloud.dataflow.sdk.coders

Class DelegateCoder<T,IntermediateT>

java.lang.Object

com.google.cloud.dataflow.sdk.coders.StandardCoder<T>

com.google.cloud.dataflow.sdk.coders.DeterministicStandardCoder<T>

com.google.cloud.dataflow.sdk.coders.AtomicCoder<T>

com.google.cloud.dataflow.sdk.coders.CustomCoder<T>

com.google.cloud.dataflow.sdk.coders.DelegateCoder<T,IntermediateT>

Type Parameters:

T - The type of objects coded by this Coder.

IntermediateT - The type of objects a T will be converted to for coding.

All Implemented Interfaces:

Coder<T>, Serializable

Direct Known Subclasses:

StringDelegateCoder

public class DelegateCoder<T,IntermediateT>
extends CustomCoder<T>

A DelegateCoder<T, IntermediateT> wraps a Coder for IntermediateT and encodes/decodes values of type T by converting to/from IntermediateT and then encoding/decoding using the underlying Coder<IntermediateT>.

The conversions from T to IntermediateT and vice versa must be supplied as DelegateCoder.CodingFunction, a serializable function that may throw any Exception. If a thrown exception is an instance of CoderException or IOException, it will be re-thrown, otherwise it will be wrapped as a CoderException.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	DelegateCoder.CodingFunction<InputT,OutputT> A CodingFunction<InputT, OutputT> is a serializable function from InputT to OutputT that may throw any Exception.

Nested classes/interfaces inherited from interface com.google.cloud.dataflow.sdk.coders.Coder

Coder.Context, Coder.NonDeterministicException

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	DelegateCoder(Coder<IntermediateT> coder, DelegateCoder.CodingFunction<T,IntermediateT> toFn, DelegateCoder.CodingFunction<IntermediateT,T> fromFn)

Method Summary

Modifier and Type	Method and Description
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.
Collection<String>	getAllowedEncodings() A collection of encodings supported by Coder.decode(java.io.InputStream, com.google.cloud.dataflow.sdk.coders.Coder.Context) in addition to the encoding from Coder.getEncodingId() (which is assumed supported).
Coder<IntermediateT>	getCoder() Returns the coder used to encode/decode the intermediate values produced/consumed by the coding functions of this DelegateCoder.
String	getEncodingId() An identifier for the binary format written by Coder.encode(T, java.io.OutputStream, com.google.cloud.dataflow.sdk.coders.Coder.Context).
static <T,IntermediateT> DelegateCoder<T,IntermediateT>	of(Coder<IntermediateT> coder, DelegateCoder.CodingFunction<T,IntermediateT> toFn, DelegateCoder.CodingFunction<IntermediateT,T> fromFn)
Object	structuralValue(T value) Returns an object with an Object.equals() method that represents structural equality on the argument.
String	toString()
void	verifyDeterministic() Throw Coder.NonDeterministicException if the coding is not deterministic.

Methods inherited from class com.google.cloud.dataflow.sdk.coders.CustomCoder

asCloudObject, of

Methods inherited from class com.google.cloud.dataflow.sdk.coders.AtomicCoder

getCoderArguments, getInstanceComponents

Methods inherited from class com.google.cloud.dataflow.sdk.coders.StandardCoder

consistentWithEquals, equals, getComponents, getEncodedElementByteSize, hashCode, isRegisterByteSizeObserverCheap, registerByteSizeObserver, verifyDeterministic, verifyDeterministic

Methods inherited from class java.lang.Object

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

Constructor Detail

DelegateCoder

protected DelegateCoder(Coder<IntermediateT> coder,
                        DelegateCoder.CodingFunction<T,IntermediateT> toFn,
                        DelegateCoder.CodingFunction<IntermediateT,T> fromFn)

Method Detail

of

public static <T,IntermediateT> DelegateCoder<T,IntermediateT> of(Coder<IntermediateT> coder,
                                                                  DelegateCoder.CodingFunction<T,IntermediateT> toFn,
                                                                  DelegateCoder.CodingFunction<IntermediateT,T> fromFn)

encode

public void encode(T value,
                   OutputStream outStream,
                   Coder.Context context)
            throws CoderException,
                   IOException

Description copied from interface: Coder

Encodes the given value of type T onto the given output stream in the given context.

Throws:

CoderException - if the value could not be encoded for some reason

IOException - if writing to the OutputStream fails for some reason

decode

public T decode(InputStream inStream,
                Coder.Context context)
         throws CoderException,
                IOException

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:

CoderException - if the value could not be decoded for some reason

IOException - if reading from the InputStream fails for some reason

getCoder

public Coder<IntermediateT> getCoder()

Returns the coder used to encode/decode the intermediate values produced/consumed by the coding functions of this DelegateCoder.

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 interface Coder<T>

Overrides:

verifyDeterministic in class CustomCoder<T>

Throws:

NonDeterministicException - when the underlying coder's verifyDeterministic() throws a Coder.NonDeterministicException. For this to be safe, the intermediate CodingFunction<T, IntermediateT> must also be deterministic.

Coder.NonDeterministicException - if this coder is not deterministic.

structuralValue

public Object structuralValue(T value)
                       throws Exception

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>

Returns:

a structural for a value of type T obtained by first converting to IntermediateT and then obtaining a structural value according to the underlying coder.

Throws:

Exception

toString

public String toString()

Overrides:

toString in class StandardCoder<T>

getEncodingId

public String getEncodingId()

An identifier for the binary format written by Coder.encode(T, java.io.OutputStream, com.google.cloud.dataflow.sdk.coders.Coder.Context).

This value, along with the fully qualified class name, forms an identifier for the binary format of this coder. Whenever this value changes, the new encoding is considered incompatible with the prior format: It is presumed that the prior version of the coder will be unable to correctly read the new format and the new version of the coder will be unable to correctly read the old format.

If the format is changed in a backwards-compatible way (the Coder can still accept data from the prior format), such as by adding optional fields to a Protocol Buffer or Avro definition, and you want Dataflow to understand that the new coder is compatible with the prior coder, this value must remain unchanged. It is then the responsibility of Coder.decode(java.io.InputStream, com.google.cloud.dataflow.sdk.coders.Coder.Context) to correctly read data from the prior format.

Specified by:

getEncodingId in interface Coder<T>

Overrides:

getEncodingId in class CustomCoder<T>

Returns:

a String composed from the underlying coder class name and its encoding id. Note that this omits any description of the coding functions. These should be modified with care.

getAllowedEncodings

public Collection<String> getAllowedEncodings()

A collection of encodings supported by Coder.decode(java.io.InputStream, com.google.cloud.dataflow.sdk.coders.Coder.Context) in addition to the encoding from Coder.getEncodingId() (which is assumed supported).

This information is not currently used for any purpose. It is descriptive only, and this method is subject to change.

Specified by:

getAllowedEncodings in interface Coder<T>

Overrides:

getAllowedEncodings in class StandardCoder<T>

Returns:

allowed encodings which are composed from the underlying coder class and its allowed encoding ids. Note that this omits any description of the coding functions. These should be modified with care.

See Also:

Coder.getEncodingId()