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From "Bert Brecht (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-6645) Refactored DocumentObjectBinder and added AnnotationListeners
Date Tue, 04 Nov 2014 19:31:34 GMT

    [ https://issues.apache.org/jira/browse/SOLR-6645?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14196659#comment-14196659
] 

Bert Brecht commented on SOLR-6645:
-----------------------------------

maybe, we can at least introduce a factory. So, everyone would be able to override the DocumentObjectBinder
with his own class and we only have to find a way to tell the factory which FQCN should be
used?
Making it smooth, we could also introduce an abstract class and so on...

brgds,
Bert

> Refactored DocumentObjectBinder and added AnnotationListeners
> -------------------------------------------------------------
>
>                 Key: SOLR-6645
>                 URL: https://issues.apache.org/jira/browse/SOLR-6645
>             Project: Solr
>          Issue Type: Improvement
>          Components: clients - java
>    Affects Versions: 4.10.2
>            Reporter: Fabio Piro
>              Labels: annotations, binder, listener, solrj
>             Fix For: 5.0, Trunk
>
>         Attachments: SOLR-6645.patch
>
>
> Hello good people.
> It is understandable that the priority of SolrJ is to provide a stable API for java and
not a rich-feature client, I'm well aware of that. On the other hand more features nowadays
mean most of the time Spring Solr Data. Although I appreciate the enrichment work of that
lib, sometimes depending on its monolithic dependencies and magic is not a valid option.
> So, I was thinking that the official DocumentObjectBinder could benefit from some love,
and I had implemented a listener pattern for the annotations. 
> *Note: No new logic or new annotations were introduced, the patch is only a refactor
to make more extendible (for the user) the current DocumentObjectBinder and @Field DocField.*
> You can register your annotations and they relate listeners in the binder, and it will
invoke the corresponding method in the listener on getBean and on toSolrInputDocument, therefore
granting the chance to do something during the ongoing process.
> Changes are:
> * [MOD] */beans/DocumentObjectBinder*:  The new logic and a new constructor for registering
the annotations
> * [ADD] */impl/AccessorAnnotationListener*: Abstract utility class with the former get(),
set(), isArray, isList, isContainedInMap etc...
> * [ADD] */impl/FieldAnnotationListener*: all the rest of DocField for dealing with @Field
> * [ADD] */AnnotationListener*: the base listener class
> * [MOD] */SolrServer*: added setBinder (this is the only tricky change, I hope it's not
a problem).
> It's all well documented and the code is very easy to read. Tests are all green, it should
be 100% backward compatible and the performance impact is void (the logic flow is exactly
the same as now, and I only changed the bare essentials and nothing more, anyway).
> Some Examples (they are not part of the pull-request):
> The long awaited @FieldObject in 4 lines of code:
> https://issues.apache.org/jira/browse/SOLR-1945
> {code:java}
> public class FieldObjectAnnotationListener extends AccessorAnnotationListener<FieldObject>
{
>     public FieldObjectAnnotationListener(AnnotatedElement element, FieldObject annotation)
{
>         super(element, annotation);
>     }
>     @Override
>     public void onGetBean(Object obj, SolrDocument doc, DocumentObjectBinder binder)
{
>         Object nested = binder.getBean(target.clazz, doc);
>         setTo(obj, nested);
>     }
>     @Override
>     public void onToSolrInputDocument(Object obj, SolrInputDocument doc, DocumentObjectBinder
binder) {
>         SolrInputDocument nested = binder.toSolrInputDocument(getFrom(obj));
>         for (Map.Entry<String, SolrInputField> entry : nested.entrySet()) {
>             doc.addField(entry.getKey(), entry.getValue());
>         }
>     }
> }
> {code}
> Or something entirely new like an annotation for ChildDocuments:
> {code:java}
> public class ChildDocumentsAnnotationListener extends AccessorAnnotationListener<ChildDocuments>
{
>     public ChildDocumentsAnnotationListener(AnnotatedElement element, ChildDocuments
annotation) {
>         super(element, annotation);
>         if (!target.isInList || target.clazz.isPrimitive()) {
>             throw new BindingException("@NestedDocuments is applicable only on List<Object>.");
>         }
>     }
>     @Override
>     public void onGetBean(Object obj, SolrDocument doc, DocumentObjectBinder binder)
{
>         List<Object> nested = new ArrayList<>();
>         for (SolrDocument child : doc.getChildDocuments()) {
>             nested.add(binder.getBean(target.clazz, child));// this should be recursive,
but it's only an example
>         }
>         setTo(obj, nested);
>     }
>     @Override
>     public void onToSolrInputDocument(Object obj, SolrInputDocument doc, DocumentObjectBinder
binder) {
>         SolrInputDocument nested = binder.toSolrInputDocument(getFrom(obj));
>         doc.addChildDocuments(nested.getChildDocuments());
>     }
> }
> {code}
> In addition, all the logic is encapsulated in the listener, so you can make a custom
FieldAnnotationListener too, and override the default one
> {code:java}
> public class CustomFieldAnnotationListener extends FieldAnnotationListener {
>     private boolean isTransientPresent;
>     public CustomFieldAnnotationListener(AnnotatedElement element, Field annotation)
{
>         super(element, annotation);
>         this.isTransientPresent = element.isAnnotationPresent(Transient.class);
>     }
>     @Override
>     public void onGetBean(Object obj, SolrDocument doc, DocumentObjectBinder binder)
{
>         if(!isTransientPresent){
>             super.onGetBean(obj, doc, binder);
>         }
>     }
>     @Override
>     public void onToSolrInputDocument(Object obj, SolrInputDocument doc, DocumentObjectBinder
binder) {
>         if(!isTransientPresent){
>             super.onToSolrInputDocument(obj, doc, binder);
>         }
>     }
> }
> {code}
> I think this is a good solution for a win-win scenario:
> - The code is almost unchanged (only shifted, wisely changed) so there is no new code
to test and to support for the devs.
> - People who only need the plain @Field will be untouched and unaware of the change.
> - People who need some extra functionalities (like converters) can now easily extend
the @Field logic, or make new annotations.
> - With some luck, a Community-Driven repository with the most useful features can emerge.
> - [Bonus] The binder is now entirely documented and not so scarier like before (we are
almost at Halloween, but still... :) )
>  The code is production-ready, if you are interested in merging it to the core, we can
discuss the last touch (mainly what to leave protected and what to set private).
> ---
> Update1: Added PATCH



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