Package alluxio.extensions

Class ExtensionFactoryRegistry<T extends ExtensionFactory<?,​S>,​S extends AlluxioConfiguration>

  • Type Parameters:
    T - The type of extension factory
    S - the type of configuration to be used when creating the extension
    @NotThreadSafe
public class ExtensionFactoryRegistry<T extends ExtensionFactory<?,​S>,​S extends AlluxioConfiguration>
extends java.lang.Object

    An extension registry that uses the ServiceLoader mechanism to automatically discover available factories and provides a central place for obtaining actual extension instances.

    Registering New Factories

    New factories can be registered either using the ServiceLoader based automatic discovery mechanism or manually using the static #register(T) method. The down-side of the automatic discovery mechanism is that the discovery order is not controllable. As a result if your implementation is designed as a replacement for one of the standard implementations, depending on the order in which the JVM discovers the services your own implementation may not take priority. You can enable DEBUG level logging for this class to see the order in which factories are discovered and which is selected when obtaining a ExtensionFactoryRegistry instance for a path. If this shows that your implementation is not getting discovered or used, you may wish to use the manual registration approach.

    Automatic Discovery

    To use the ServiceLoader based mechanism you need to have a file with the same name as the factory class T placed in the META-INF\services directory of your project. This file should contain the full name of your factory types (one per line), your factory types must have a public unparameterised constructor available (see ServiceLoader for more detail on this). You can enable DEBUG level logging to see factories as they are discovered if you wish to check that your implementation gets discovered.

    Manual Registration

    To manually register a factory, simply pass an instance of your factory to the #register(T) method. This can be useful when your factory cannot be instantiated without arguments or in cases where automatic discovery does not give your factory priority. Factories registered this way will be registered at the start of the factories list so will have the first opportunity to indicate whether they support a requested path.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      static java.lang.String UNKNOWN_VERSION  

    • Constructor Summary

      Constructors 
      Constructor Description
      ExtensionFactoryRegistry​(java.lang.Class<T> factoryClass, java.lang.String extensionPattern)
      Constructs a registry for loading extension of a particular type.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      java.util.List<T> findAllWithRecorder​(java.lang.String path, S conf, Recorder recorder)
      Finds all the factories that support the given path and record the detailed execution process.
      java.util.List<T> getAvailable()
      Returns a read-only view of the available base factories.
      void register​(T factory)
      Registers a new factory.
      void reset()
      Resets the registry to its default state
      java.util.List<T> scanRegistered​(java.lang.String path, S conf)
      Finds factories from registered collection.
      void unregister​(T factory)
      Unregisters an existing factory.

      • Methods inherited from class java.lang.Object

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

    • Field Detail

    • Constructor Detail

      • ExtensionFactoryRegistry

        public ExtensionFactoryRegistry​(java.lang.Class<T> factoryClass,
                                java.lang.String extensionPattern)
        Constructs a registry for loading extension of a particular type.
        Parameters:
        factoryClass - the type of the extension factory
        extensionPattern - the pattern used to select libraries to be loaded

    • Method Detail

      • getAvailable

        public java.util.List<T> getAvailable()
        Returns a read-only view of the available base factories.
        Returns:
        Read-only view of the available base factories

      • findAllWithRecorder

        public java.util.List<T> findAllWithRecorder​(java.lang.String path,
                                             S conf,
                                             Recorder recorder)
        Finds all the factories that support the given path and record the detailed execution process.
        Parameters:
        path - path
        conf - configuration of the extension
        recorder - recorder used to record the detailed execution process
        Returns:
        list of factories that support the given path which may be an empty list

      • scanRegistered

        public java.util.List<T> scanRegistered​(java.lang.String path,
                                        S conf)
        Finds factories from registered collection.
        Parameters:
        path - path
        conf - configuration of the extension
        Returns:
        list of factories that support the given path which may be an empty list

      • register

        public void register​(T factory)
        Registers a new factory.

        Factories are registered at the start of the factories list so they can override the existing automatically discovered factories. Generally if you use the ServiceLoader mechanism properly it should be unnecessary to call this, however since ServiceLoader discovery order may be susceptible to class loader behavioral differences there may be rare cases when you need to manually register the desired factory.

        Parameters:
        factory - factory to register

      • reset

        public void reset()
        Resets the registry to its default state

        This clears the registry as it stands and rediscovers the available factories.

      • unregister

        public void unregister​(T factory)
        Unregisters an existing factory.
        Parameters:
        factory - factory to unregister