com.datastax.driver.core

Class CodecRegistry

java.lang.Object

com.datastax.driver.core.CodecRegistry

public final class CodecRegistry
extends Object

A registry for TypeCodecs. When the driver needs to serialize or deserialize a Java type to/from CQL, it will lookup in the registry for a suitable codec. The registry is initialized with default codecs that handle basic conversions (e.g. CQL text to java.lang.String), and users can add their own. Complex codecs can also be generated on-the-fly from simpler ones (more details below).

Creating a registry

By default, the driver uses DEFAULT_INSTANCE, a shareable, JVM-wide instance initialized with built-in codecs for all the base CQL types. The only reason to create your own instances is if you have multiple Cluster objects that use different sets of codecs. In that case, use Cluster.Builder.withCodecRegistry(CodecRegistry) to associate the registry with the cluster:

 CodecRegistry myCodecRegistry = new CodecRegistry();
 myCodecRegistry.register(myCodec1, myCodec2, myCodec3);
 Cluster cluster = Cluster.builder().withCodecRegistry(myCodecRegistry).build();

 // To retrieve the registry later:
 CodecRegistry registry = cluster.getConfiguration().getCodecRegistry();
 

CodecRegistry instances are thread-safe.

It is possible to turn on log messages by setting the com.datastax.driver.core.CodecRegistry logger level to TRACE. Beware that the registry can be very verbose at this log level.

Registering and using custom codecs

To create a custom codec, write a class that extends TypeCodec, create an instance, and pass it to one of the register methods; for example, one could create a codec that maps CQL timestamps to JDK8's java.time.LocalDate:

 class LocalDateCodec extends TypeCodec<java.time.LocalDate> {
    ...
 }
 myCodecRegistry.register(new LocalDateCodec());
 

The conversion will be available to:

• all driver types that implement GettableByIndexData, GettableByNameData, SettableByIndexData and/or SettableByNameData. Namely: Row, BoundStatement, UDTValue and TupleValue;
• simple statements;
• statements created with the Query builder.

Example:

 Row row = session.executeQuery("select date from some_table where pk = 1").one();
 java.time.LocalDate date = row.get(0, java.time.LocalDate.class); // uses LocalDateCodec registered above
 

You can also bypass the codec registry by passing a standalone codec instance to methods such as GettableByIndexData.get(int, TypeCodec).

Codec generation

When a CodecRegistry cannot find a suitable codec among existing ones, it will attempt to create it on-the-fly. It can manage:

• collections (lists, sets and maps) of known types. For example, if you registered a codec for JDK8's java.time.LocalDate like in the example above, you get List<LocalDate>> and Set<LocalDate>> handled for free, as well as all Map types whose keys and/or values are java.time.LocalDate. This works recursively for nested collections;
• user types, mapped to UDTValue objects. Custom codecs are available recursively to the UDT's fields, so if one of your fields is a timestamp you can use your LocalDateCodec to retrieve it as a java.time.LocalDate;
• tuple types, mapped to TupleValue (with the same rules for nested fields);
• custom types, mapped to ByteBuffer.

If the codec registry encounters a mapping that it can't handle automatically, a CodecNotFoundException is thrown; you'll need to register a custom codec for it.

Performance and caching

Whenever possible, the registry will cache the result of a codec lookup for a specific type mapping, including any generated codec. For example, if you registered LocalDateCodec and ask the registry for a codec to convert a CQL list<timestamp> to a Java List<LocalDate>:

1. the first lookup will generate a TypeCodec<List<LocalDate>> from LocalDateCodec, and put it in the cache;
2. the second lookup will hit the cache directly, and reuse the previously generated instance.

The javadoc for each codecFor variant specifies whether the result can be cached or not.

Codec order

When the registry looks up a codec, the rules of precedence are:

• if a result was previously cached for that mapping, it is returned;
• otherwise, the registry checks the list of built-in codecs – the default ones – and the ones that were explicitly registered (in the order that they were registered). It calls each codec's accepts methods to determine if it can handle the mapping, and if so returns it;
• otherwise, the registry tries to generate a codec, according to the rules outlined above.

It is currently impossible to override an existing codec. If you try to do so, register(TypeCodec) will log a warning and ignore it.

Field Summary

Fields

Modifier and Type	Field and Description
static CodecRegistry	DEFAULT_INSTANCE The default CodecRegistry instance.

Constructor Summary

Constructors

Constructor and Description
CodecRegistry() Creates a new instance initialized with built-in codecs for all the base CQL types.

Method Summary

Modifier and Type	Method and Description
<T> TypeCodec<T>	codecFor(DataType cqlType) Returns a codec that accepts the given CQL type.
<T> TypeCodec<T>	codecFor(DataType cqlType, Class<T> javaType) Returns a codec that accepts the given CQL type and the given Java class.
<T> TypeCodec<T>	codecFor(DataType cqlType, T value) Returns a codec that accepts the given CQL type and the given value.
<T> TypeCodec<T>	codecFor(DataType cqlType, TypeToken<T> javaType) Returns a codec that accepts the given CQL type and the given Java type.
<T> TypeCodec<T>	codecFor(T value) Returns a codec that accepts the given value.
CodecRegistry	register(Iterable<? extends TypeCodec<?>> codecs) Register the given codecs with this registry.
CodecRegistry	register(TypeCodec<?>... codecs) Register the given codecs with this registry.
CodecRegistry	register(TypeCodec<?> newCodec) Register the given codec with this registry.

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_INSTANCE

public static final CodecRegistry DEFAULT_INSTANCE

The default CodecRegistry instance.

It will be shared among all Cluster instances that were not explicitly built with a different instance.

Constructor Detail

CodecRegistry

public CodecRegistry()

Creates a new instance initialized with built-in codecs for all the base CQL types.

Method Detail

register

public CodecRegistry register(TypeCodec<?> newCodec)

Register the given codec with this registry.

This method will log a warning and ignore the codec if it collides with a previously registered one. Note that this check is not done in a completely thread-safe manner; codecs should typically be registered at application startup, not in a highly concurrent context (if a race condition occurs, the worst possible outcome is that no warning gets logged, and the codec gets registered but will never actually be used).

Parameters:

newCodec - The codec to add to the registry.

Returns:

this CodecRegistry (for method chaining).

register

public CodecRegistry register(TypeCodec<?>... codecs)

Register the given codecs with this registry.

Parameters:

codecs - The codecs to add to the registry.

Returns:

this CodecRegistry (for method chaining).

See Also:

register(TypeCodec)

register

public CodecRegistry register(Iterable<? extends TypeCodec<?>> codecs)

Register the given codecs with this registry.

Parameters:

codecs - The codecs to add to the registry.

Returns:

this CodecRegistry (for method chaining).

See Also:

register(TypeCodec)

codecFor

public <T> TypeCodec<T> codecFor(T value)

Returns a codec that accepts the given value.

This method takes an arbitrary Java object and tries to locate a suitable codec for it. Codecs must perform a runtime inspection of the object to determine if they can accept it or not, which, depending on the implementations, can be expensive; besides, the resulting codec cannot be cached. Therefore there might be a performance penalty when using this method.

Furthermore, this method returns the first matching codec, regardless of its accepted CQL type. It should be reserved for situations where the target CQL type is not available or unknown. In the Java driver, this happens mainly when serializing a value in a SimpleStatement or in the QueryBuilder, where no CQL type information is available.

Codecs returned by this method are NOT cached (see the top-level documentation of this class for more explanations about caching).

Parameters:

value - The value the codec should accept; must not be null.

Returns:

A suitable codec.

Throws:

CodecNotFoundException - if a suitable codec cannot be found.

codecFor

public <T> TypeCodec<T> codecFor(DataType cqlType)
                          throws CodecNotFoundException

Returns a codec that accepts the given CQL type.

This method returns the first matching codec, regardless of its accepted Java type. It should be reserved for situations where the Java type is not available or unknown. In the Java driver, this happens mainly when deserializing a value using the getObject method.

Codecs returned by this method are cached (see the top-level documentation of this class for more explanations about caching).

Parameters:

cqlType - The CQL type the codec should accept; must not be null.

Returns:

A suitable codec.

Throws:

CodecNotFoundException - if a suitable codec cannot be found.

codecFor

public <T> TypeCodec<T> codecFor(DataType cqlType,
                                 Class<T> javaType)
                          throws CodecNotFoundException

Returns a codec that accepts the given CQL type and the given Java class.

This method can only handle raw (non-parameterized) Java types. For parameterized types, use codecFor(DataType, TypeToken) instead.

Codecs returned by this method are cached (see the top-level documentation of this class for more explanations about caching).

Parameters:

cqlType - The CQL type the codec should accept; must not be null.

javaType - The Java type the codec should accept; can be null.

Returns:

A suitable codec.

Throws:

CodecNotFoundException - if a suitable codec cannot be found.

codecFor

public <T> TypeCodec<T> codecFor(DataType cqlType,
                                 TypeToken<T> javaType)
                          throws CodecNotFoundException

Returns a codec that accepts the given CQL type and the given Java type.

This method handles parameterized types thanks to Guava's TypeToken API.

Codecs returned by this method are cached (see the top-level documentation of this class for more explanations about caching).

Parameters:

cqlType - The CQL type the codec should accept; must not be null.

javaType - The Java type the codec should accept; can be null.

Returns:

A suitable codec.

Throws:

CodecNotFoundException - if a suitable codec cannot be found.

codecFor

public <T> TypeCodec<T> codecFor(DataType cqlType,
                                 T value)

Returns a codec that accepts the given CQL type and the given value.

This method takes an arbitrary Java object and tries to locate a suitable codec for it. Codecs must perform a runtime inspection of the object to determine if they can accept it or not, which, depending on the implementations, can be expensive; besides, the resulting codec cannot be cached. Therefore there might be a performance penalty when using this method.

Codecs returned by this method are NOT cached (see the top-level documentation of this class for more explanations about caching).

Parameters:

cqlType - The CQL type the codec should accept; can be null.

value - The value the codec should accept; must not be null.

Returns:

A suitable codec.

Throws:

CodecNotFoundException - if a suitable codec cannot be found.