Package org.axonframework.eventsourcing.eventstore

Interface EventTypeResolver

Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface EventTypeResolver
Read-side resolver that constructs a MessageType from the stored qualified name and version of a stored event.

The write-side counterpart, MessageTypeResolver, derives a MessageType from a payload class at dispatch time. This interface handles the opposite direction, specifically for events that are reconstructed from a storage solution. Given the stored qualifiedName and (possibly null or empty) version, it returns the MessageType to use when reading a stored event.

The default resolver, obtained from DEFAULT, substitutes "0.0.0" for any missing or empty stored version. This ensures that events stored by Axon Framework 4 (which allowed a null revision) can be read by Axon Framework 5 without any schema migration. Use withDefaultVersion(String) to override the substituted version when "0.0.0" does not suit your needs.

Implementations are permitted to rewrite the qualifiedName, but doing so is discouraged: semantic event evolution belongs in the transformation layer, not in version normalization. This interface is intentionally narrow; keep implementations focused on resolving a missing version.

Since:
5.1.2
Author:
Steven van Beelen

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final EventTypeResolver
    DEFAULT
    A EventTypeResolver that substitutes "0.0.0" for any null or empty stored version, and passes the stored version through unchanged when present.
    static final String
    MISSING_VERSION_DEFAULT
    The version substituted for null or empty versions by the DEFAULT event type resolver.

  • Method Summary

    Modifier and Type
    Method
    Description
    MessageType
    resolve(String qualifiedName, @Nullable String version)
    Resolves the MessageType for an event read from the event store.
    static EventTypeResolver
    withDefaultVersion(String defaultVersion)
    Returns a EventTypeResolver that substitutes the given defaultVersion for any null or empty stored version, and passes the stored version through unchanged when present.

  • Field Details

    • MISSING_VERSION_DEFAULT

      static final String MISSING_VERSION_DEFAULT
      The version substituted for null or empty versions by the DEFAULT event type resolver.

      Set to "0.0.0", deliberately distinct from MessageType.DEFAULT_VERSION (0.0.1), so legacy AF4 events without a revision always sort as older than any explicitly versioned event.

      See Also:

    • DEFAULT

      static final EventTypeResolver DEFAULT
      A EventTypeResolver that substitutes "0.0.0" for any null or empty stored version, and passes the stored version through unchanged when present.

  • Method Details

    • withDefaultVersion

      static EventTypeResolver withDefaultVersion(String defaultVersion)
      Returns a EventTypeResolver that substitutes the given defaultVersion for any null or empty stored version, and passes the stored version through unchanged when present.
      Parameters:
      defaultVersion - the version to use when the stored version is absent; must not be null or empty
      Returns:
      a EventTypeResolver that substitutes the given defaultVersion for any null or empty stored version, and passes the stored version through unchanged when present
      Throws:
      AxonConfigurationException - if the given defaultVersion is null or empty

    • resolve

      MessageType resolve(String qualifiedName, @Nullable String version)
      Resolves the MessageType for an event read from the event store.
      Parameters:
      qualifiedName - the qualified name of the event as stored; never null
      version - the version of the event as stored; may be null or empty for events written by Axon Framework 4, which allowed a null revision
      Returns:
      the MessageType to use for the event; never null