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![SQL2
SELECT * FROM [cq:PageContent] AS s
WHERE ISDESCENDANTNODE([/content])
AND s.[jcr:title] = ’Moja strona’
• Main purpose: find node by property contents
• Avoid queries with parent path (as it’s not
indexed)
– It’s better to create a mixin or marker property
• We don’t JOIN
• SQL and XPath are isomorphic](https://image.slidesharecdn.com/jcrandsling-130919035854-phpapp02/85/Shooting-rabbits-with-sling-8-320.jpg)
![Paragraph system
<c:forEach var=‚par‛ items=‚${resource.children}‛>
<sling:include
path=‚${par.path}‛
resourceType=‚${par[‘sling:resourceType’]}‛/>
</c:forEach>
Left column
Article
list
Twitter
widget
Contact
info](https://image.slidesharecdn.com/jcrandsling-130919035854-phpapp02/85/Shooting-rabbits-with-sling-27-320.jpg)
Uploaded byTomasz Rękawek
Shooting rabbits with sling
Apache Sling provides RESTful access to content stored in an Apache Jackrabbit content repository. Sling uses a resource-centric approach where everything is represented as a resource that can be rendered in different formats. Resources map directly to nodes in the Jackrabbit content tree. Sling supports scripting languages like JSP and uses selectors, extensions and resource types to determine how each resource should be rendered. It allows composing page resources from multiple child resources.
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Shooting rabbits with sling
- 1. Shooting rabbits withsling Introduction to Apache Jackrabbit & Apache Sling
- 2. JCR • Content RepositoryAPI for Java • JSR-170 & JSR-283 • javax.jcr • Object database • Hierarchical data model • Apache Jackrabbit – reference implementation
- 3. Mantra: everything iscontent • Content is content – Blogs, articles, posts, etc. • Structured data – List of addresses in e-mail database • Unstructured data – Word document • ACLs • Code
- 4. Content hierarchy • JCRhas tree-like data model • Repository consists of items • Item can be node or property • Node children are properties or other nodes • Properties are leaves
- 5. Node • Nodes formcontent hierarchy • Nodes are named • Each node has primary type specifying it’s structure (allowed and required children and properties) – Something like class – Eg. myapp:Contact requires properties myapp:givenName and myapp:familyName • Nodes can also have mixin types – Something like interface – Eg. mix:versionable, mix:lockable or myapp:Emailable • Popular types: – nt:base, nt:unstructured, nt:folder
- 6. Property • Property containsdata • Types: – string, binary, long, double, date, boolean, name, path, reference • Can be multivalued
- 7. Searching • Node namesand properties are indexed • Jackrabbit uses Apache Lucene • Supported query languages: – XPath – JCR-SQL – JCR-SQL2 (recommended)
- 8. SQL2 SELECT * FROM[cq:PageContent] AS s WHERE ISDESCENDANTNODE([/content]) AND s.[jcr:title] = ’Moja strona’ • Main purpose: find node by property contents • Avoid queries with parent path (as it’s not indexed) – It’s better to create a mixin or marker property • We don’t JOIN • SQL and XPath are isomorphic
- 9. Versioning • Any subtreecan be versioned • Add mixin mix:versionable • node.checkin() – Creates new version – Makes the node read-only • node.checkout() – Allows to modify the node • Usage examples: – Page versions at many levels
- 10. Observation • Event listener •We can filter events with: – Event type – Path – Node types – An explicit list of nodes • Usage examples: – Automatic workflows – Generating thumbnails – “Last modified” date – Indexing in internal and external search engine
- 11. Other features • Locking •Access control – Users & groups – Groups can be members of other groups – Privileges on nodes to read, write, etc.
- 12. JCR – advantagesand problems • Advantages – Site structure is easy to reflect – Flexible – Hierarchical structure • Disadvantages – Storing large amount of structured data is neither easy nor efficient • Don’t load CSV file with 1 000 000 rows – Data has to be denormalized (as there is no JOINs) – Clustering is tricky • Master-slave works OK • Waiting for Jackrabbit 3.0 – codename Oak – Transactions…
- 13. Apache Sling HTTP accessto JCR repository
- 14. Apache Sling • Webframework • RESTful access to JCR nodes • Powered by OSGi • Support multiple scripting languages (JSP, Groovy, …) • Open source, developed by Adobe within Apache foundation
- 15. REST # Create /Update $ curl -u admin:admin –d name=‚Java User Group‛ –d city=Poznan localhost:8080/content/hello # Read $ curl localhost:8080/content/hello.tidy.json # Delete $ curl -X DELETE -u admin:admin localhost:8080/content/hello
- 16. Resource URL • Resourcepath: /content/hello – http://localhost:8080/content/hello.xml – http://localhost:8080/content/hello.json – http://localhost:8080/content/hello.html • There are simple built-in renderers • Each can be overridden
- 17. sling:resourceType • In orderto create custom rendition we need to set sling:resourceType property • It’s a JCR path to some renderer • Renderer can be JSP, Java Servlet, Scala, Python, Groovy, Ruby or ESP (internal Sling language, kind of backend JS) • Content-centric: you don’t invoke script directly
- 18. Sample HTML renderer <html> <head><title>ESPexample</title> </head> <body> <h1> Hello <%= currentNode.getProperty('name') %> </h1> <h2> <%= currentNode.getProperty('city') %> </h2> </body> </html>
- 19. How does itwork? • Get node path from URL • Get extension • Get HTTP method GET /content/home.html • Find sling:resourceType • Choose appropriate script (POST.jsp, json.jsp, e tc.) /apps/jug/hellocomponent • Render node using found renderer and appropriate script Hello JUG!
- 20. URL decomposition /content/corporate/jobs/developer.print.a4.html/mysuffix • Resourcepath • Selectors • Extension • Suffix
- 21. Resource path /content/corporate/jobs/developer.print.a4.html/mysuffix • Substringbefore the first dot • Path to the resource in JCR • This part of the URL defines data. – Rest defines way of the presentation.
- 22. Extension /content/corporate/jobs/developer.print.a4.html/mysuffix • Defines contentformat • Most common: html, json, xml • But may be png
- 23. Selectors /content/corporate/jobs/developer.print.a4.html/mysuffix • Specifies additionalvariants of the given content type • Optional • Multiple selectors are allowed
- 24. Suffix /content/corporate/jobs/developer.print.a4.html/mysuffix • Additional informationpassed to the rendering script • Similar to GET ?name=value parameter, but can be cached
- 25. Script resolution GET /content/corporate/jobs/developer.print.a4.html/mysuffix /content/corporate/jobs/developer/sling:resourceType= cognifide/hr/jobs /apps/cognifide/hr/jobs: 1. jobs.print.a4.GET.html.esp 2. jobs.print.a4.html.esp 3. jobs.print.a4.esp 4. jobs.print.GET.html.esp 5. jobs.print.html.esp 6. jobs.print.esp 7. jobs.GET.html.esp 8. jobs.html.esp 9. jobs.GET.esp 10. jobs.esp
- 26. Composed resources Page title Left columnMain <html> <head><title><%= currentNode.getProperty(’title') %></title></head> <body> <div class=‚left_column‛> <sling:include path=‚left‛ resourceType=‚foundation/parsys‛/> </div> <div class=‚main‛> <sling:include path=‚main‛ resourceType=‚foundation/parsys‛/> <div> </body> </html>
- 27. Paragraph system <c:forEach var=‚par‛items=‚${resource.children}‛> <sling:include path=‚${par.path}‛ resourceType=‚${par[‘sling:resourceType’]}‛/> </c:forEach> Left column Article list Twitter widget Contact info
- 28. Resource Resolver • InJCR we had Node • In Sling we have Resource • Virtual tree of resources, reflecting the JCR • ResourceResolver – transforms nodes to resources • It’s possible to create own ResourceResolvers and reflect other data sources – Filesystem, – MongoDB, – PostgreSQL • Many ResourceResolvers may work together – Like mount in UNIX
- 29. Resolver usage Resource res= resourceResolver.getResource(‚/content/hello‛); ModifiableValueMap map = res.adaptTo(ModifiableValueMap.class); String name = map.get(‚name‛, String.class); map.put(‚name‛, name.toUpperCase()); resourceResolver.commit(); Node node = res.adaptTo(javax.jcr.Node); Session = resourceResolver.adaptTo(javax.jcr.Session);
- 30. Why do weuse resolver? • API is friendlier than JCR • Sling provides us resources and resolver in many places – Servlets – Scripts
- 31. Servlets • Like ordinaryservlets but… • Can be assigned to: – Paths – Selectors – Extensions – Resource types (so can act as rendering script) • doGet(), doPost() methods are invoked with – SlingHttpServletRequest and …Response – Additional methods for getting requested resource, resolver, decompose URL, etc.
- 32. Sample Sling servlet @Component @Service @SlingServlet(resourceTypes= ‛jug/hellocomponent‛) public class AuthCheckerServlet extends SlingSafeMethodsServlet { @Reference private ResourceResolverFactory resolverFactory; public void doGet(SlingHttpServletRequest request, SlingHttpServletResponse response) { response.getWriter().println(‚Hello world‛); } }
- 33. Sling – prosand cons • Similar to JCR • Pros – Natural reflection of site and filesystem structure • Document repositories, Digital Asset Management – OSGi stack – Javascript has easy access to repository • Cons – Security issues • internal resources available as xml and json, • handling user generated content – Lack of free tools, eg. repo explorer
- 34.