ResolverHookFactory
Date: 2016-06-24

org.osgi.framework.hooks.resolver

## Interface ResolverHookFactory

-     @ConsumerType
      public interface ResolverHookFactory

  OSGi Framework Resolver Hook Factory Service.

  Bundles registering this service will be called by the framework during a bundle resolver process to obtain a `resolver hook` instance which will be used for the duration of a resolve process.

  See Also:
    `ResolverHook`

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `ResolverHook` | `begin(java.util.Collection<BundleRevision> triggers)` This method is called by the framework each time a resolve process begins to obtain a `resolver hook` instance.

- - ### Method Detail

    - #### begin

          ResolverHook begin(java.util.Collection<BundleRevision> triggers)

      This method is called by the framework each time a resolve process begins to obtain a `resolver hook` instance. This resolver hook instance will be used for the duration of the resolve process. At the end of the resolve process the method `ResolverHook.end()` must be called by the framework and the framework must not hold any references of the resolver hook instance.

      The triggers represent the collection of bundles which triggered the resolve process. This collection may be empty if the triggers cannot be determined by the framework. In most cases the triggers can easily be determined. Calling certain methods on `bundle` when a bundle is in the `INSTALLED` state will cause the framework to begin a resolve process in order to resolve the bundle. The following methods will start a resolve process in this case:

      - `start`
      - `loadClass`
      - `findEntries`
      - `getResource`
      - `getResources`
      In such cases the collection will contain the single bundle which the framework is trying to resolve. Other cases will cause multiple bundles to be included in the trigger bundles collection. When `resolveBundles` is called the collection of triggers must include all the current bundle revisions for bundles passed to resolveBundles which are in the `INSTALLED` state.

      When `FrameworkWiring.refreshBundles(Collection, org.osgi.framework.FrameworkListener...)` is called the collection of triggers is determined with the following steps:

      - If the collection of bundles passed is null then `FrameworkWiring.getRemovalPendingBundles()` is called to get the initial collection of bundles.
      - The equivalent of calling `FrameworkWiring.getDependencyClosure(Collection)` is called with the initial collection of bundles to get the dependency closure collection of the bundles being refreshed.
      - Remove any non-active bundles from the dependency closure collection.
      - For each bundle remaining in the dependency closure collection get the current bundle revision and add it to the collection of triggers.

      As described above, a resolve process is typically initiated as a result of calling API that causes the framework to attempt to resolve one or more bundles. The framework is free to start a resolve process at any time for reasons other than calls to framework API. For example, a resolve process may be used by the framework for diagnostic purposes and result in no bundles actually becoming resolved at the end of the process. Resolver hook implementations must be prepared for resolve processes that are initiated for other reasons besides calls to framework API.

      Parameters:
        `triggers` - an unmodifiable collection of bundles which triggered the resolve process. This collection may be empty if the collection of trigger bundles cannot be determined.
      Returns:
        a resolver hook instance to be used for the duration of the resolve process. A `null` value may be returned which indicates this resolver hook factory abstains from the resolve process.