[dna-issues] [JBoss JIRA] Resolved: (DNA-270) Simplify the ExecutionContext framework

[Randall Hauch (JIRA)]

     [ https://jira.jboss.org/jira/browse/DNA-270?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Randall Hauch resolved DNA-270.
-------------------------------

    Resolution: Done


Changed ExecutionContext from an interface to a concrete class, and made it implement ExecutionContextFactory.  This allowed removing the BasicExecutionContext and BasicExecutionContextFactory implementations.  Also added methods to ExecutionContext to create "subcontext" (or context that inherit all of the same components except for one), allowing removal of the ExecutionContexts class.  These changes made it much easier to use (no need to know about an implementation, anybody can create a context or create a modified form of another context, less of a distinction between ExecutionContext and ExecutionContextFactory, etc.), yet provides a lot of flexibility for defining different combinations of components (including custom components) without requiring subclassing (though subclassing is not precluded).

There were two primary subinterfaces of ExecutionContext (SequencerContext and JcrExecutionContext); both of these were converted from classes to interfaces, eliminating their implementation classes.  Since both provide special kinds of contexts that only added components to the "context" (rather than changing the behavior of the existing components).

Also changed the documentation and examples to reflect these improvements.

> Simplify the ExecutionContext framework
> ---------------------------------------
>
>                 Key: DNA-270
>                 URL: https://jira.jboss.org/jira/browse/DNA-270
>             Project: DNA
>          Issue Type: Task
>          Components: API, Connectors, Documentation, Examples, Graph, Sequencers
>    Affects Versions: 0.3
>            Reporter: Randall Hauch
>            Assignee: Randall Hauch
>             Fix For: 0.4
>
>         Attachments: dna-270.patch
>
>
> The ExecutionContext interface is used throughout the system.  It's defined in 'dna-graph', and used to represent the context or environment for executing various activities.  There is also ExecutionContextFactory, which is an interface for creating other contexts with different JAAS security contexts (login context or access control contexts).  There are also the Basic* implementations of these interfaces, as well as several subclasses (with various implementations).
> The idea of using an interface for this was to simplify the design of the components that uses/took an ExecutionContext, to prevent propagating dependencies, and to allow customization.  However, since ExecutionContext is largely just an aggregation of references, there's little need to customize the behavior, and this doesn't really add any other dependencies to the classpath (all implementations of the aggregated components are already in 'dna-graph') and it doesn't expose any implementations through the method signatures.  Using interfaces also complicates the usage, since clients have to know about the concrete implementations.  This is even more true when they're setting up the DNA services and repositories in 'dna-repository' and 'dna-jcr'.
> So, consider changing this interface to a concrete class, with methods that make it easy to create instances as well as instances with custom components (e.g., a new context that is the same as 'this' but with a supplied NamespaceRegistry implementation).
> This will change the public API, but this should be acceptable given that we're not yet at 1.0 (and this really improves both the client code, and doesn't really change extension implementations).

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