Class FilesystemMetadataResolver

All Implemented Interfaces:
Iterable<EntityDescriptor>, Component, DestructableComponent, IdentifiableComponent, IdentifiedComponent, InitializableComponent, Resolver<EntityDescriptor,​CriteriaSet>, IterableMetadataSource, BatchMetadataResolver, MetadataResolver, RefreshableMetadataResolver

public class FilesystemMetadataResolver
extends AbstractReloadingMetadataResolver
A metadata provider that pulls metadata from a file on the local filesystem. This metadata provider periodically checks to see if the read metadata file has changed. The delay between each refresh interval is calculated as follows. If no validUntil or cacheDuration is present then the AbstractReloadingMetadataResolver.getMaxRefreshDelay() value is used. Otherwise, the earliest refresh interval of the metadata file is checked by looking for the earliest of all the validUntil attributes and cacheDuration attributes. If that refresh interval is larger than the max refresh delay then AbstractReloadingMetadataResolver.getMaxRefreshDelay() is used. If that number is smaller than the min refresh delay then AbstractReloadingMetadataResolver.getMinRefreshDelay() is used. Otherwise the calculated refresh delay multiplied by AbstractReloadingMetadataResolver.getRefreshDelayFactor() is used. By using this factor, the provider will attempt to be refresh before the cache actually expires, allowing a some room for error and recovery. Assuming the factor is not exceedingly close to 1.0 and a min refresh delay that is not overly large, this refresh will likely occur a few times before the cache expires.
  • Field Details

    • log

      private final org.slf4j.Logger log
      Class logger.
    • metadataFile

      @Nonnull private File metadataFile
      The metadata file.
  • Constructor Details

    • FilesystemMetadataResolver

      public FilesystemMetadataResolver​(@Nonnull File metadata) throws ResolverException
      Constructor.
      Parameters:
      metadata - the metadata file
      Throws:
      ResolverException - this exception is no longer thrown
    • FilesystemMetadataResolver

      public FilesystemMetadataResolver​(@Nullable Timer backgroundTaskTimer, @Nonnull File metadata) throws ResolverException
      Constructor.
      Parameters:
      metadata - the metadata file
      backgroundTaskTimer - timer used to refresh metadata in the background
      Throws:
      ResolverException - this exception is no longer thrown
  • Method Details

    • setMetadataFile

      protected void setMetadataFile​(@Nonnull File file) throws ResolverException
      Sets the file from which metadata is read.
      Parameters:
      file - path to the metadata file
      Throws:
      ResolverException - this exception is no longer thrown
    • doDestroy

      protected void doDestroy()
      Overrides:
      doDestroy in class AbstractReloadingMetadataResolver
    • getMetadataIdentifier

      protected String getMetadataIdentifier()
      Gets an identifier which may be used to distinguish this metadata in logging statements.
      Specified by:
      getMetadataIdentifier in class AbstractReloadingMetadataResolver
      Returns:
      identifier which may be used to distinguish this metadata in logging statements
    • fetchMetadata

      protected byte[] fetchMetadata() throws ResolverException
      Fetches metadata from a source.
      Specified by:
      fetchMetadata in class AbstractReloadingMetadataResolver
      Returns:
      the fetched metadata, or null if the metadata is known not to have changed since the last retrieval
      Throws:
      ResolverException - thrown if there is a problem fetching the metadata
    • validateMetadataFile

      protected void validateMetadataFile​(@Nonnull File file) throws ResolverException
      Validate the basic properties of the specified metadata file, for example that it exists; that it is a file; and that it is readable.
      Parameters:
      file - the file to evaluate
      Throws:
      ResolverException - if file does not pass basic properties required of a metadata file