[SLING-3709] Sling Models: Allow caller to deal with exceptions

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Sling Models Implementation 1.0.4, Sling Models Implementation 1.0.6
• Fix Version/s: Sling Models API 1.2.0, Sling Models Impl 1.2.0
• Component/s: Extensions
• Labels: models
• Assignee: Konrad Windszus
• Reporter: Konrad Windszus
• Created: 30/Jun/14 07:32
• Updated: 02/Oct/19 15:02
• Resolved: 20/May/15 14:41

Description

Currently due to the specification of the adaptTo-method to return null if adaptation is not possible, the caller is not notified about any exceptions (because they are caught within the ModelAdapterFactory).

This is e.g. necessary to deal with validation exceptions properly (i.e. required field injection not possible). The problem was also discussed briefly in http://apache-sling.73963.n3.nabble.com/Silng-Models-Validation-Framework-td4033411.html.

All exceptions either being thrown by the
@PostConstruct method or caused by the field/method injection are not propagated but basically swallowed by Sling Models.

It would be great to be able to catch those exceptions either in the view or in a servlet filter. I think it should be possible to throw unchecked exceptions in the ModelAdapterFactory.getFactory() method if it is requested (i.e. through a global OSGi configuration flag for Sling Models).
WDYT?
Would you accept such a patch or do you think this breaks the API (also compare with https://issues.apache.org/jira/browse/SLING-2712?focusedCommentId=13561516&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13561516).

If it does not work through the adaptTo, SlingModels should provide an alternative way of instanciating models (and propagating exceptions), although this is kind of tricky, because it internally relies on adaptTo as well (e.g. in https://github.com/apache/sling/blob/trunk/bundles/extensions/models/impl/src/main/java/org/apache/sling/models/impl/ModelAdapterFactory.java#L647)

Issue Links

• breaks: SLING-4056 ModelFactory.canCreateFromAdaptable reports false errors when using "adapters" on models
• is related to: SLING-7978 Sling Mocks: Allow easy access to the ModelFactory
• is related to: SLING-8758 Add Adaptable method with a non-null return value
• is required by: SLING-4447 Improve JavaUseProvider to not fall back to a simple Pojo instantiation in case a Java class with @Model annotation cannot be instantiated
• relates to: SLING-3714 Allow for a caller to request a non-null response from adaptTo()