sling component filters in cq5

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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• The Sling Request Invocation Chain

• Implementing own Sling Filters

• Use Cases and Samples

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Agenda

!!!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.

The Sling Request Invocation Chain

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How the Sling Engine processes HTTP Requests

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

Implementing Sling Filters

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How to use Filters as Extensionpoint

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.

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);

}

}

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

Check Filterconditions at first place

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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


}

}

• Check available Information from slingRequest if Filter should do anything.

• Be aware that these checks may be performed a lot especially for COMPONENT scope

Accessing and Using Data in Filter

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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()

"\">");


writer.write("</component>");

return;

}

}


}

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!

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.

Usecases & Samples

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Usecases

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• Logging

• Measuring

• Decoration

• Pre-Processing

• Post-Processing

• Manipulating Inclusions

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

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.

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)

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

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)

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

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)

;)

http://www.adaptto.org/

Berlin pro!vision GmbH Wilmersdorfer Str. 50-51 10627 Berlin Germany Tel. +49 (30) 818828-50 E-Mail [email protected]

Frankfurt pro!vision GmbH Löwengasse 27 A 60385 Frankfurt am Main Germany Tel. +49 (69) 8700328-0 E-Mail [email protected]

Karim Khan Tel. +49 (69) 8700328-0 E-Mail [email protected]

Contact

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mailto:[email protected]









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