[GitHub] [struts] lukaszlenart commented on pull request #528: Potential expression cache enhancement for 2.6 series

[GitBox <gi...@apache.org>]

lukaszlenart commented on PR #528:
URL: https://github.com/apache/struts/pull/528#issuecomment-1087197928

   Yeah... I'm planning to write a guideline how to use Struts DI mechanism, it can be hard to understand on the first glimpse ;-)
   
   You can try to follow my changes in this [PR](https://github.com/apache/struts/pull/529/files) - I introduced an injectable date formatter with two default implementations, but users can provide they own if needed.
   
   So the whole trick is that you must define an extension point: `struts.ognl.expressionCacheFactory` (in my PR it was `struts.date.formatter`) and supporting interface/class that will be used together `OgnlCacheFactory` (`DateFormatter` in my PR). Now in `StrutsBeanSelectionProvider` you must register an alias which ties the extension point with the backing interface/class - in my case it was 
   
   ```
   alias(DateFormatter.class, StrutsConstants.STRUTS_DATE_FORMATTER, builder, props, Scope.SINGLETON);
   ```
   
   (your PR is missing this step, sorry that I didn't spot it ealy :( )
   
   Having that set, either you can make this a required dependency and provide at least one implementation of the interface/class or make it optional and handle nulls in your code.
   
   In my case I made it required and provided two implementations: `SimpleDateFormatAdapter` named `simpleDateFormatAdapter` (as a bean name) and `DateTimeFormatterAdapter` named `dateTimeFormatterAdapter` - the names can be of your choice, they to not play any role yet.
   
   Now you must register the beans in Struts DI:
   
   ```
   <bean type="org.apache.struts2.components.date.DateFormatter" name="simpleDateFormatter" class="org.apache.struts2.components.date.SimpleDateFormatAdapter" scope="singleton"/>
   <bean type="org.apache.struts2.components.date.DateFormatter" name="dateTimeFormatter" class="org.apache.struts2.components.date.DateTimeFormatterAdapter" scope="singleton"/>
   ```
   
   ^^ this ties implementation with the name.
   
   And now it's time to tell Struts DI which implementation to use for the extension point:
   
   ```
   struts.date.formatter=dateTimeFormatter
   ```
   
   and done! :)
   
   With such approach users can define they own implementations and used them with the extension point.
   
   If something is still unclear please ask, I will try to prepare the guideline.


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