Presentation “Sling Component Filters in CQ5“ by Dominik Süss at CQCON2013 in Basel on 19 and 20 June 2013.

1. Understanding & Utilizing Apache Sling Filters in Adobe CQ5 / AEM
Dominik Süß, Senior Developer, pro!vision GmbH
Sling Component Filters in CQ5
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2. • The Sling Request Invocation Chain
• Implementing own Sling Filters
• Use Cases and Samples
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Agenda

3. !!!WARNING!!!
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Sling Filters are a very generic and mighty extensionpoint. When
utilizing them you should always have in mind that AEM/CQ Core
functionality relies on the data provided by Sling, manipulation
of this data therefore may break CQ.

4. The Sling Request Invocation Chain
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How the Sling Engine processes HTTP Requests

5. FilterManager
Sling Request Invocation Chain
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SlingMainServlet
FilterChain
Scope: REQUEST
FilterChain
Scope: COMPONENT
Filter A
Filter B
Filter C
Registered as Services
(preferably via SCR Annotation)
Component Servlet
processRequest()dispatchRequest()
INCLUDE/FORWARD
SlingRequestProcessor

6. Implementing Sling Filters
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How to use Filters as Extensionpoint

7. Registration of Filters
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• Standard Servlet Filter (javax.servlet.Filter)
– Need to be registered as Service („manually“ or SlingFilter SCR Annotation)
• Order and FilterScopes can be defined
• Order defined by Serviceranking
• Filterscopes
– REQUEST
– COMPONENT
– ERROR
– INCLUDE *
– FORWARD *
* FilterChain executes COMPONENT scope for these scopes as well.

8. SCR Annotation
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@SlingFilter(scope = SlingFilterScope.COMPONENT, order = -10000, metatype =
false)
public class MyComponentFilter implements javax.servlet.Filter {
@Override
public void doFilter(ServletRequest pRequest, ServletResponse pResponse,
FilterChain pChain) throws IOException, ServletException {
// Implement Filter
// continue with filter chaining
pChain.doFilter(pRequest, pResponse);
}
}

9. Filter Order
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• Existing Filters might use the deprecated „filter.order“ instead
„service.ranking“
• NOTE: SLING-2920 was identified while verifying this behavior – look up the
mailing list for further information how to use it for now
• Existing Filters and their execution ORDER can be inspected via
– http://<instance>:<port>/system/console/status-slingfilter

10. Check Filterconditions at first place
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public void doFilter(ServletRequest pRequest, ServletResponse pResponse,
FilterChain pChain) throws IOException, ServletException {
if (!(pRequest instanceof SlingHttpServletRequest)) {
throw new ServletException("Request is not a Sling HTTP request.");
}
if (isFilterEnabled(slingRequest)) {
// Implement Filter-Logic
} else {
// continue with filter chaining
pChain.doFilter(pRequest, pResponse);
}
}
• Check available Information from slingRequest if Filter should do anything.
• Be aware that these checks may be performed a lot especially for COMPONENT scope

11. Accessing and Using Data in Filter
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public void doFilter(ServletRequest pRequest, ServletResponse pResponse,
FilterChain pChain) throws IOException, ServletException {
if (!(pRequest instanceof SlingHttpServletRequest)) {
throw new ServletException("Request is not a Sling HTTP request.");
}
if (isFilterEnabled(slingRequest)) {
Resource resource = slingRequest.getResource(); // already resolved
if (null != resource) {
PrintWriter writer = pResponse.getWriter();
writer.write("<component resourceType="" + resource.getResourceType()
"">");
pChain.doFilter(pRequest, pResponse);
writer.write("</component>");
return;
}
}
pChain.doFilter(pRequest, pResponse);
}

12. Useful Wrapper Objects in Filters
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• SlingHttpServletRequestWrapper
– Implement to override parts of the request
• E.g. Inject impersonated ResourceResolver*
• SlingHttpServletResponseWrapper
– Implement to inject additional logic to response
• E.g. inject own writer to buffer the response to perform some postprocessing
* Security-Note: Make sure you don’t create security holes this way – the request
should always respect the permissions of the current user!

13. Dispatch to other Resource
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RequestDispatcher dispatcher =
slingRequest.getRequestDispatcher(otherResource);
dispatcher.forward(request, response);
Required in any situation where you need to redirect the request.
Note: You should be aware that a Dispatcher Forward or Include will retrigger
the FilterChain. Place such filters early in the Filterchain to prevent other
Filters to be executed twice.

14. Usecases & Samples
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15. Usecases
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• Logging
• Measuring
• Decoration
• Pre-Processing
• Post-Processing
• Manipulating Inclusions

16. Logging
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• Allows to hook in Requestcentric logging at Sling Level
• It is possible to log even requests/includes of components which are not
part of the own application (like foundation components)
• Sample
– org.apache.sling.engine.impl.debug.RequestProgressTrackerLogFilter

17. Measuring
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• Since the Filterchain gets consulted at each call of a component they
provide a natural location to measure the actual usage of the system
• The concrete usecases depend on the goal of the application
• You should just add additional measuring if no other techniques like
loganalysis or available reports are not sufficient.

18. Decoration
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• Adding generic but usecasespecific decoration to components
• Sample
– WCMDebugFilter ( for Requestparameter debug=layout)
• Further Usecase
– For specific selector: Metadata for third party systems like
• Search Parsers
• Integrating Systems (e.g. Portals)

19. Preprocessing
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• Injecting data that needs to be available within the components
• Sample:
– WCMComponentFilter – generic logic that links CQ Authoring logic with Sling
Components
– I18nFilter – Injecting I18n Resource Bundles
• Further Usecases
– Build Java Bean and place in Request to be used via jsp:useBean and EL within
JSPs (Sepearation of businesslogic)*
* Just a proof of concept, impact of preprocessing on performance yet untested

20. Postprocessing
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• Injecting custom writer to postprocess output
• Sample:
– RewriterFilter
• Further Usecases:
– Integration of thirt party markup (e.g. via Velocity or Freemarker)
– Injection of a generic Placeholderlogic (e.g. Personalization)

21. Manipulating Inclusions
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• Redirecting , Skipping or manipulating further processing
• Samples:
– Mobile RedirectFilter (trigger Redirect with matching selector for device)
– TimeWarp Filter ( replacing ResourceData & corresponding Objects with Objects at
given Timestamp)
• Further Usecases
– Controlled Impersonation in Author Mode for Permissionpreview
(Publishpermissions)
– Component Level Caching (Record response to cache and answer subsequent
requests from cache)*
* Not yet verified, but might be a solution for partial caching where dispatcher caches
cannot be used

22. Some last words…
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• The Apache Sling Stack is the core of CQ5 / AEM
• Apache Sling is an open source project that relies on an active community
• So – be part the community!
– Join the User and/or Dev Mailinglist
– File Bugs and contribute Patches
– Participate in community events to drive evolution of Apache Sling …
… like adaptTo() 2013 in Berlin (http://www.adaptto.org)
;)

23. Berlin
pro!vision GmbH
Wilmersdorfer Str. 50-51
10627 Berlin
Germany
Tel. +49 (30) 818828-50
E-Mail info@pro-vision.de
Frankfurt
pro!vision GmbH
Löwengasse 27 A
60385 Frankfurt am Main
Germany
Tel. +49 (69) 8700328-0
E-Mail info@pro-vision.de
Karim Khan
Tel. +49 (69) 8700328-0
E-Mail kkhan@pro-vision.de
Contact
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