Package org.apache.flink.api.common.typeutils.base

Class MapSerializer<K,​V>

  • Type Parameters:
    K - The type of the keys in the map.
    V - The type of the values in the map.
    All Implemented Interfaces:
    Serializable
    @Internal
public final class MapSerializer<K,​V>
extends TypeSerializer<Map<K,​V>>
    A serializer for Map. The serializer relies on a key serializer and a value serializer for the serialization of the map's key-value pairs.

    The serialization format for the map is as follows: four bytes for the length of the map, followed by the serialized representation of each key-value pair. To allow null values, each value is prefixed by a null marker.

    See Also:
    Serialized Form

    • Constructor Detail

      • MapSerializer

        public MapSerializer​(TypeSerializer<K> keySerializer,
                     TypeSerializer<V> valueSerializer)
        Creates a map serializer that uses the given serializers to serialize the key-value pairs in the map.
        Parameters:
        keySerializer - The serializer for the keys in the map
        valueSerializer - The serializer for the values in the map

    • Method Detail

      • isImmutableType

        public boolean isImmutableType()
        Description copied from class: TypeSerializer
        Gets whether the type is an immutable type.
        Specified by:
        isImmutableType in class TypeSerializer<Map<K,​V>>
        Returns:
        True, if the type is immutable.

      • duplicate

        public TypeSerializer<Map<K,​V>> duplicate()
        Description copied from class: TypeSerializer
        Creates a deep copy of this serializer if it is necessary, i.e. if it is stateful. This can return itself if the serializer is not stateful.

        We need this because Serializers might be used in several threads. Stateless serializers are inherently thread-safe while stateful serializers might not be thread-safe.

        Specified by:
        duplicate in class TypeSerializer<Map<K,​V>>

      • copy

        public Map<K,​V> copy​(Map<K,​V> from)
        Description copied from class: TypeSerializer
        Creates a deep copy of the given element in a new element.
        Specified by:
        copy in class TypeSerializer<Map<K,​V>>
        Parameters:
        from - The element reuse be copied.
        Returns:
        A deep copy of the element.

      • copy

        public Map<K,​V> copy​(Map<K,​V> from,
                           Map<K,​V> reuse)
        Description copied from class: TypeSerializer
        Creates a copy from the given element. The method makes an attempt to store the copy in the given reuse element, if the type is mutable. This is, however, not guaranteed.
        Specified by:
        copy in class TypeSerializer<Map<K,​V>>
        Parameters:
        from - The element to be copied.
        reuse - The element to be reused. May or may not be used.
        Returns:
        A deep copy of the element.

      • getLength

        public int getLength()
        Description copied from class: TypeSerializer
        Gets the length of the data type, if it is a fix length data type.
        Specified by:
        getLength in class TypeSerializer<Map<K,​V>>
        Returns:
        The length of the data type, or -1 for variable length data types.

      • serialize

        public void serialize​(Map<K,​V> map,
                      DataOutputView target)
               throws IOException
        Description copied from class: TypeSerializer
        Serializes the given record to the given target output view.
        Specified by:
        serialize in class TypeSerializer<Map<K,​V>>
        Parameters:
        map - The record to serialize.
        target - The output view to write the serialized data to.
        Throws:
        IOException - Thrown, if the serialization encountered an I/O related error. Typically raised by the output view, which may have an underlying I/O channel to which it delegates.

      • deserialize

        public Map<K,​V> deserialize​(DataInputView source)
                           throws IOException
        Description copied from class: TypeSerializer
        De-serializes a record from the given source input view.
        Specified by:
        deserialize in class TypeSerializer<Map<K,​V>>
        Parameters:
        source - The input view from which to read the data.
        Returns:
        The deserialized element.
        Throws:
        IOException - Thrown, if the de-serialization encountered an I/O related error. Typically raised by the input view, which may have an underlying I/O channel from which it reads.

      • deserialize

        public Map<K,​V> deserialize​(Map<K,​V> reuse,
                                  DataInputView source)
                           throws IOException
        Description copied from class: TypeSerializer
        De-serializes a record from the given source input view into the given reuse record instance if mutable.
        Specified by:
        deserialize in class TypeSerializer<Map<K,​V>>
        Parameters:
        reuse - The record instance into which to de-serialize the data.
        source - The input view from which to read the data.
        Returns:
        The deserialized element.
        Throws:
        IOException - Thrown, if the de-serialization encountered an I/O related error. Typically raised by the input view, which may have an underlying I/O channel from which it reads.

      • copy

        public void copy​(DataInputView source,
                 DataOutputView target)
          throws IOException
        Description copied from class: TypeSerializer
        Copies exactly one record from the source input view to the target output view. Whether this operation works on binary data or partially de-serializes the record to determine its length (such as for records of variable length) is up to the implementer. Binary copies are typically faster. A copy of a record containing two integer numbers (8 bytes total) is most efficiently implemented as target.write(source, 8);.
        Specified by:
        copy in class TypeSerializer<Map<K,​V>>
        Parameters:
        source - The input view from which to read the record.
        target - The target output view to which to write the record.
        Throws:
        IOException - Thrown if any of the two views raises an exception.

      • snapshotConfiguration

        public TypeSerializerSnapshot<Map<K,​V>> snapshotConfiguration()
        Description copied from class: TypeSerializer
        Snapshots the configuration of this TypeSerializer. This method is only relevant if the serializer is used to state stored in checkpoints/savepoints.

        The snapshot of the TypeSerializer is supposed to contain all information that affects the serialization format of the serializer. The snapshot serves two purposes: First, to reproduce the serializer when the checkpoint/savepoint is restored, and second, to check whether the serialization format is compatible with the serializer used in the restored program.

        IMPORTANT: TypeSerializerSnapshots changed after Flink 1.6. Serializers implemented against Flink versions up to 1.6 should still work, but adjust to new model to enable state evolution and be future-proof. See the class-level comments, section "Upgrading TypeSerializers to the new TypeSerializerSnapshot model" for details.

        Specified by:
        snapshotConfiguration in class TypeSerializer<Map<K,​V>>
        Returns:
        snapshot of the serializer's current configuration (cannot be null).
        See Also:
        TypeSerializerSnapshot.resolveSchemaCompatibility(TypeSerializerSnapshot)