com.datastax.driver.extras.codecs

Class MappingCodec<O,I>

java.lang.Object

com.datastax.driver.core.TypeCodec<O>

com.datastax.driver.extras.codecs.MappingCodec<O,I>

Type Parameters:

O - The "outer" (user-facing) Java type

I - The "inner" (Cassandra-facing, intermediary) Java type

Direct Known Subclasses:

OptionalCodec, OptionalCodec

public abstract class MappingCodec<O,I>
extends TypeCodec<O>

An abstract TypeCodec that maps a Java Pojo to another Java object that can in turn be serialized into a CQL type. This can serve as a base for libraries dealing with Pojo mappings.

This codec can be seen as a convenience base class for libraries dealing with Pojo-to-Pojo mappings, but it comes with a performance penalty: each Java object is serialized in two steps: first to an intermediate object, and then to a ByteBuffer, which means that each serialization actually incurs in two potentially expensive operations being carried.

If such operations are really expensive, and your mapping library is capable of serializing objects directly to ByteBuffers, consider writing your own codec instead of using this one.

Nested Class Summary

Nested classes/interfaces inherited from class com.datastax.driver.core.TypeCodec

TypeCodec.AbstractCollectionCodec<E,C extends Collection<E>>, TypeCodec.AbstractMapCodec<K,V>, TypeCodec.AbstractTupleCodec<T>, TypeCodec.AbstractUDTCodec<T>, TypeCodec.PrimitiveBooleanCodec, TypeCodec.PrimitiveByteCodec, TypeCodec.PrimitiveDoubleCodec, TypeCodec.PrimitiveFloatCodec, TypeCodec.PrimitiveIntCodec, TypeCodec.PrimitiveLongCodec, TypeCodec.PrimitiveShortCodec

Field Summary

Fields

Modifier and Type	Field and Description
protected TypeCodec<I>	innerCodec

Fields inherited from class com.datastax.driver.core.TypeCodec

cqlType, javaType

Constructor Summary

Constructors

Constructor and Description
MappingCodec(TypeCodec<I> innerCodec, Class<O> javaType)
MappingCodec(TypeCodec<I> innerCodec, com.google.common.reflect.TypeToken<O> javaType)

Method Summary

Modifier and Type	Method and Description
O	deserialize(ByteBuffer bytes, ProtocolVersion protocolVersion) Deserialize the given ByteBuffer instance according to the CQL type handled by this codec.
protected abstract O	deserialize(I value)
String	format(O value) Format the given value as a valid CQL literal according to the CQL type handled by this codec.
O	parse(String value) Parse the given CQL literal into an instance of the Java type handled by this codec.
protected abstract I	serialize(O value)
ByteBuffer	serialize(O value, ProtocolVersion protocolVersion) Serialize the given value according to the CQL type handled by this codec.

Methods inherited from class com.datastax.driver.core.TypeCodec

accepts, accepts, accepts, accepts, ascii, bigint, blob, cboolean, cdouble, cfloat, cint, counter, custom, date, decimal, getCqlType, getJavaType, inet, list, map, set, smallInt, time, timestamp, timeUUID, tinyInt, toString, tuple, userType, uuid, varchar, varint

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

innerCodec

protected final TypeCodec<I> innerCodec

Constructor Detail

MappingCodec

public MappingCodec(TypeCodec<I> innerCodec,
                    Class<O> javaType)

MappingCodec

public MappingCodec(TypeCodec<I> innerCodec,
                    com.google.common.reflect.TypeToken<O> javaType)

Method Detail

serialize

public ByteBuffer serialize(O value,
                            ProtocolVersion protocolVersion)
                     throws InvalidTypeException

Description copied from class: TypeCodec

Serialize the given value according to the CQL type handled by this codec.

Implementation notes:

1. Null values should be gracefully handled and no exception should be raised; these should be considered as the equivalent of a NULL CQL value;
2. Codecs for CQL collection types should not permit null elements;
3. Codecs for CQL collection types should treat a null input as the equivalent of an empty collection.

Specified by:

serialize in class TypeCodec<O>

Parameters:

value - An instance of T; may be null.

protocolVersion - the protocol version to use when serializing bytes. In most cases, the proper value to provide for this argument is the value returned by ProtocolOptions.getProtocolVersion() (which is the protocol version in use by the driver).

Returns:

A ByteBuffer instance containing the serialized form of T

Throws:

InvalidTypeException - if the given value does not have the expected type

deserialize

public O deserialize(ByteBuffer bytes,
                     ProtocolVersion protocolVersion)
              throws InvalidTypeException

Description copied from class: TypeCodec

Deserialize the given ByteBuffer instance according to the CQL type handled by this codec.

Implementation notes:

1. Null or empty buffers should be gracefully handled and no exception should be raised; these should be considered as the equivalent of a NULL CQL value and, in most cases, should map to null or a default value for the corresponding Java type, if applicable;
2. Codecs for CQL collection types should clearly document whether they return immutable collections or not (note that the driver's default collection codecs return mutable collections);
3. Codecs for CQL collection types should avoid returning null; they should return empty collections instead (the driver's default collection codecs all comply with this rule).
4. The provided ByteBuffer should never be consumed by read operations that modify its current position; if necessary, ByteBuffer.duplicate() duplicate} it before consuming.

Specified by:

deserialize in class TypeCodec<O>

Parameters:

bytes - A ByteBuffer instance containing the serialized form of T; may be null or empty.

protocolVersion - the protocol version to use when serializing bytes. In most cases, the proper value to provide for this argument is the value returned by ProtocolOptions.getProtocolVersion() (which is the protocol version in use by the driver).

Returns:

An instance of T

Throws:

InvalidTypeException - if the given ByteBuffer instance cannot be deserialized

parse

public O parse(String value)
        throws InvalidTypeException

Description copied from class: TypeCodec

Parse the given CQL literal into an instance of the Java type handled by this codec.

Implementors should take care of unquoting and unescaping the given CQL string where applicable. Null values and empty Strings should be accepted, as well as the string "NULL"; in most cases, implementations should interpret these inputs has equivalent to a null reference.

Implementing this method is not strictly mandatory: internally, the driver only uses it to parse the INITCOND when building the metadata of an aggregate function (and in most cases it will use a built-in codec, unless the INITCOND has a custom type).

Specified by:

parse in class TypeCodec<O>

Parameters:

value - The CQL string to parse, may be null or empty.

Returns:

An instance of T; may be null on a null input.

Throws:

InvalidTypeException - if the given value cannot be parsed into the expected type

format

public String format(O value)
              throws InvalidTypeException

Description copied from class: TypeCodec

Format the given value as a valid CQL literal according to the CQL type handled by this codec.

Implementors should take care of quoting and escaping the resulting CQL literal where applicable. Null values should be accepted; in most cases, implementations should return the CQL keyword "NULL" for null inputs.

Implementing this method is not strictly mandatory. It is used:

1. in the query builder, when values are inlined in the query string (see BuiltStatement for a detailed explanation of when this happens);
2. in the QueryLogger, if parameter logging is enabled;
3. to format the INITCOND in AggregateMetadata.asCQLQuery(boolean);
4. in the toString() implementation of some objects (UDTValue, TupleValue, and the internal representation of a ROWS response), which may appear in driver logs.

If you choose not to implement this method, you should not throw an exception but instead return a constant string (for example "XxxCodec.format not implemented").

Specified by:

format in class TypeCodec<O>

Parameters:

value - An instance of T; may be null.

Returns:

CQL string

Throws:

InvalidTypeException - if the given value does not have the expected type

deserialize

protected abstract O deserialize(I value)

serialize

protected abstract I serialize(O value)