[jira] [Commented] (LOG4J2-3474) Use PluginBuilder for instantiating plugins

["Matt Sicker (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LOG4J2-3474?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17520755#comment-17520755 ] 

Matt Sicker commented on LOG4J2-3474:
-------------------------------------

Note that this has generally been addressed by the new DI system in 3.x as all plugins are instantiated via {{Injector}} now which replaces {{{}PluginBuilder{}}}. If you want to refactor 2.x such that plugin instantiation is centralized through {{{}PluginBuilder{}}}, that could be useful, too, though that mainly adds support for injecting {{@Plugin~}} annotations from config nodes. I should note that while I was working on the DI changes, I initially replaced all invocations of {{new PluginManager}} with calls to {{PluginUtil}} which made it easier to refactor and eventually remove that class once {{PluginManager}} was sufficiently integrated into Injector directly; refactoring 2.x to likewise use {{PluginUtil}} instead seems like a good idea toward maintaining consistency (and potentially making reuse of {{PluginBuilder}} et al easier there).

> Use PluginBuilder for instantiating plugins
> -------------------------------------------
>
>                 Key: LOG4J2-3474
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-3474
>             Project: Log4j 2
>          Issue Type: Bug
>          Components: Plugins
>            Reporter: Volkan Yazici
>            Priority: Major
>
> There are various places in the source code (in particular, Pattern and JSON Template layouts) where plugins are extensively used. There plugins are discovered via {{PluginManager}} but instantiated using some custom logic afterwards. This approach has serious caveats:
>  * Code duplication
>  * {{ConstraintValidator}} checks (e.g., {{{}RequiredClass{}}}) are ignored
>  * Injection is ignored
>  * All other {{PluginBuilder}} checks and functionalities are discarded and this breaks the plugin contract
> All plugins should rather be instantiated using {{{}PluginBuilder{}}}.
> This flaw also hints us that the developer-facing API of plugins is severely convoluted to the point of maintainers cannot simply discover-and-load a plugin without making a mistake. {{PluginUtil}} was an attempt to improve this situation, though it first needs to be used by the rest of the code base and it also suffers from the above custom instantiation logic shortcoming.



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