Class FileBackedHTTPMetadataResolver

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

public class FileBackedHTTPMetadataResolver
extends HTTPMetadataResolver
An HTTP metadata provider that caches a copy of the retrieved metadata to disk so that, in the event that the metadata may not be pulled from the URL, it may be pulled from disk using the most recently fetched data.

If the backup file does not already exist, it will be created by saving the byte[] retrieved in the HTTP fetch.

If isInitializeFromBackupFile() is true, then initialization will attempt to load metadata first from the backup file on disk, if it exists. If successful then the next refresh after initialization, which will attempt the full HTTP fetch, will be scheduled for the interval indicated by getBackupFileInitNextRefreshDelay(). This can help prevent large metadata batches from slowing down the synchronous resolver start up process, deferring the more expensive HTTP fetch operation to the asynchronous background refresh thread.

  • Field Details

    • log

      @Nonnull private final org.slf4j.Logger log
      Class logger.
    • metadataBackupFile

      @Nullable private File metadataBackupFile
      File containing the backup of the metadata.
    • initializing

      private boolean initializing
      Flag used to track state of whether currently initializing or not.
    • initializeFromBackupFile

      private boolean initializeFromBackupFile
      Flag indicating whether initialization should first attempt to load metadata from backup file.
    • initializedFromBackupFile

      private boolean initializedFromBackupFile
      Flag indicating whether metadata load during init was from backup file.
    • backupFileInitNextRefreshDelay

      @Nonnull private Duration backupFileInitNextRefreshDelay
      Duration after which to schedule next refresh, when initialized from backup file.
  • Constructor Details

    • FileBackedHTTPMetadataResolver

      public FileBackedHTTPMetadataResolver​(org.apache.http.client.HttpClient client, String metadataURL, String backupFilePath) throws ResolverException
      Constructor.
      Parameters:
      client - HTTP client used to fetch remote metadata
      metadataURL - the URL to fetch the metadata
      backupFilePath - the file that will keep a backup copy of the metadata,
      Throws:
      ResolverException - thrown if the URL is not a valid URL, the metadata can not be retrieved from the URL
    • FileBackedHTTPMetadataResolver

      public FileBackedHTTPMetadataResolver​(Timer backgroundTaskTimer, org.apache.http.client.HttpClient client, String metadataURL, String backupFilePath) throws ResolverException
      Constructor.
      Parameters:
      client - HTTP client used to fetch remote metadata
      backgroundTaskTimer - timer used to schedule background metadata refresh tasks
      metadataURL - the URL to fetch the metadata
      backupFilePath - the file that will keep a backup copy of the metadata,
      Throws:
      ResolverException - thrown if the URL is not a valid URL, the metadata can not be retrieved from the URL
  • Method Details

    • isInitializedFromBackupFile

      public boolean isInitializedFromBackupFile()
      Get the flag indicating whether metadata load during initialization was from backup file.
      Returns:
      true if initial load was from backup file, false otherwise
    • isInitializeFromBackupFile

      public boolean isInitializeFromBackupFile()
      Get the flag indicating whether initialization should first attempt to load metadata from backup file, if it exists.

      Defaults to: true.

      Returns:
      true if should initialize from backup file, false otherwise
    • setInitializeFromBackupFile

      public void setInitializeFromBackupFile​(boolean flag)
      Set the flag indicating whether initialization should first attempt to load metadata from backup file, if it exists.

      Defaults to: true.

      Parameters:
      flag - true if should initialize from backup file, false otherwise
    • getBackupFileInitNextRefreshDelay

      @Nonnull public Duration getBackupFileInitNextRefreshDelay()
      Get the duration after which to schedule next refresh, when initialized from backup file.

      Defaults to 5s.

      Returns:
      the duration
    • setBackupFileInitNextRefreshDelay

      public void setBackupFileInitNextRefreshDelay​(@Nonnull Duration delay)
      Set the duration after which to schedule next refresh, when initialized from backup file.

      Defaults to 5s.

      Parameters:
      delay - the next refresh delay
    • doDestroy

      protected void doDestroy()
      Overrides:
      doDestroy in class HTTPMetadataResolver
    • initMetadataResolver

      protected void initMetadataResolver() throws ComponentInitializationException
      Subclasses should override this method to perform any initialization logic necessary. Default implementation is a no-op.
      Overrides:
      initMetadataResolver in class AbstractReloadingMetadataResolver
      Throws:
      ComponentInitializationException - thrown if there is a problem initializing the provider
    • setBackupFile

      protected void setBackupFile​(String backupFilePath) throws ResolverException
      Sets the file used to backup metadata. The given file path is checked to see if it is a read/writable file if it exists or if can be created if it does not exist.
      Parameters:
      backupFilePath - path to the backup file
      Throws:
      ResolverException - thrown if the backup file is not read/writable or creatable
    • validateBackupFile

      protected void validateBackupFile​(File backupFile) throws ResolverException
      Validate the basic properties of the specified metadata backup file, for example that it exists and/or can be created; that it is not a directory; and that it is readable and writable.
      Parameters:
      backupFile - the file to evaluate
      Throws:
      ResolverException - if file does not pass basic properties required of a metadata backup file
    • fetchMetadata

      protected byte[] fetchMetadata() throws ResolverException
      Gets the metadata document from the remote server.
      Overrides:
      fetchMetadata in class HTTPMetadataResolver
      Returns:
      the metadata from remote server, or null if the metadata document has not changed since the last retrieval
      Throws:
      ResolverException - thrown if there is a problem retrieving the metadata from the remote server
    • newFilterContext

      protected MetadataFilterContext newFilterContext()
      Get a new instance of MetadataFilterContext to be used when filtering metadata.

      This default implementation will just return an empty context. Subclasses would override to add contextual info specific to the implementation.

      Overrides:
      newFilterContext in class AbstractMetadataResolver
      Returns:
      the new filter context instance
    • computeNextRefreshDelay

      @Nonnull protected Duration computeNextRefreshDelay​(@Nullable Instant expectedExpiration)
      Computes the delay until the next refresh time based on the current metadata's expiration time and the refresh interval floor.
      Overrides:
      computeNextRefreshDelay in class AbstractReloadingMetadataResolver
      Parameters:
      expectedExpiration - the time when the metadata is expected to expire and need refreshing
      Returns:
      delay until the next refresh time
    • postProcessMetadata

      protected void postProcessMetadata​(byte[] metadataBytes, Document metadataDom, XMLObject originalMetadata, XMLObject filteredMetadata) throws ResolverException
      Post-processing hook called after new metadata has been unmarshalled, filtered, and the DOM released (from the XMLObject) but before the metadata is saved off. Any exception thrown by this hook will cause the retrieved metadata to be discarded. The default implementation of this method is a no-op
      Overrides:
      postProcessMetadata in class AbstractReloadingMetadataResolver
      Parameters:
      metadataBytes - original raw metadata bytes retrieved via AbstractReloadingMetadataResolver.fetchMetadata()
      metadataDom - original metadata after it has been parsed in to a DOM document
      originalMetadata - original metadata prior to being filtered, with its DOM released
      filteredMetadata - metadata after it has been run through all registered filters and its DOM released
      Throws:
      ResolverException - thrown if there is a problem with the provided data