Class CacheEntryCodec

java.lang.Object

se.liu.ida.hefquin.federation.access.impl.cache.CacheEntryCodec

public final class CacheEntryCodec
extends Object

Codec for serializing and deserializing PersistentCacheEntry instances.

This class defines the binary format used to persist cache entries independently of the underlying storage technology. Implementations for ChronicleMap, MapDB, or other storage backends can reuse this codec to ensure a consistent on-disk representation.

Each serialized entry consists of the entry creation timestamp followed by a serialized form of the cached DataRetrievalResponse, prefixed with a type discriminator that identifies the concrete response type.

Serialization is performed into a temporary in-memory buffer before any bytes are written to the provided output. This ensures that partially serialized entries are never committed if serialization fails.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected static enum	CacheEntryCodec.CachedObjectType	Type discriminator used in the serialized format to identify the kind of cached response stored in the entry.

Method Summary

Modifier and Type	Method	Description
protected static org.apache.jena.graph.Node	deserializeNode(String s)	Parses a Jena Node from its N-Triples string representation.
static PersistentCacheEntry	read(DataInput in)	Deserializes a cache entry from the provided input.
protected static String	serializeNode(org.apache.jena.graph.Node node)	Serializes a Jena Node into its N-Triples string representation.
static void	write(DataOutput out, PersistentCacheEntry entry)	Serializes the given cache entry to the provided output.

Methods inherited from class java.lang.Object

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

Method Details

write

public static void write(DataOutput out,
 PersistentCacheEntry entry)
                  throws IOException

Serializes the given cache entry to the provided output.

Serialization is first performed into a temporary buffer and only written to out after successful completion. This prevents partially serialized entries from being persisted if an error occurs during serialization.

This method blocks until the DataRetrievalResponse contained in the cache entry becomes available.

 [creationTime: long]
 [type: int]

 SOLUTION_MAPPING_RESPONSE:
   [numMappings: int]
   repeat numMappings:
     [bindingSize: int]
     repeat bindingSize:
       [varName: UTF-8]
       [node: UTF-8]

 TPF_RESPONSE:
   [numMatchingTriples: int]
   repeat numMatchingTriples:
     [subject: UTF-8]
     [predicate: UTF-8]
     [object: UTF-8]
   [numMetadataTriples: int]
   repeat numMetadataTriples:
     [subject: UTF-8]
     [predicate: UTF-8]
     [object: UTF-8]
   [nextPageURL: UTF-8 or null]

 CARDINALITY_RESPONSE:
   [cardinality: int]
 

Parameters:

out - destination to which the serialized representation is written

entry - cache entry to serialize

Throws:

IOException - if writing to the output fails

IllegalStateException - if the response type is unsupported or the contained future cannot be resolved

read

public static PersistentCacheEntry read(DataInput in)
                                 throws IOException

Deserializes a cache entry from the provided input.

The input must contain data encoded according to the binary format defined by write(DataOutput, PersistentCacheEntry).

The deserialized response is wrapped in a completed CompletableFuture preserving the original creation timestamp.

Parameters:

in - source containing a serialized cache entry

Returns:

reconstructed cache entry

Throws:

IOException - if the serialized representation cannot be read

IllegalStateException - if an unsupported response type identifier is encountered

serializeNode

protected static String serializeNode(org.apache.jena.graph.Node node)

Serializes a Jena Node into its N-Triples string representation.

Parameters:

node - the node to serialize

deserializeNode

protected static org.apache.jena.graph.Node deserializeNode(String s)

Parses a Jena Node from its N-Triples string representation.

Parameters:

s - the serialized node