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Posted to commits@sling.apache.org by cz...@apache.org on 2012/12/12 10:14:44 UTC
svn commit: r1420577 [23/30] - in /sling/site/trunk/content/site: ./
46-line-blog.data/ authentication.data/ documentation.data/
first-steps.data/ getting-and-building-sling.data/
how-to-manage-events-in-sling.data/ index.data/ links.data/ manipulating...
Added: sling/site/trunk/content/site/request-processing.html
URL: http://svn.apache.org/viewvc/sling/site/trunk/content/site/request-processing.html?rev=1420577&view=auto
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--- sling/site/trunk/content/site/request-processing.html (added)
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+
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+<HTML>
+ <HEAD>
+ <TITLE>Apache Sling - Request Processing</TITLE>
+ <LINK rel="stylesheet" href="http://sling.apache.org/site/media.data/site.css" type="text/css" media="all">
+ <LINK rel="icon" href="http://sling.apache.org/site/media.data/favicon.ico">
+ <META http-equiv="Content-Type" content="text/html;charset=UTF-8">
+ </HEAD>
+ <BODY>
+ <DIV class="title">
+ <DIV class="logo">
+ <A href="http://sling.apache.org/site/index.html">
+ <IMG border="0" alt="Apache Sling" src="http://sling.apache.org/site/media.data/logo.png">
+ </A>
+ </DIV>
+ <DIV class="header">
+ <A href="http://www.apache.org/">
+ <IMG border="0" alt="Apache" src="http://sling.apache.org/site/media.data/apache.png">
+ </A>
+ </DIV>
+ </DIV>
+ <DIV class="menu">
+<P><B>Documentation</B><BR class="atl-forced-newline">
+<A href="getting-started.html" title="Getting Started">Getting Started</A><BR class="atl-forced-newline">
+<A href="the-sling-engine.html" title="The Sling Engine">The Sling Engine</A><BR class="atl-forced-newline">
+<A href="development.html" title="Development">Development</A><BR class="atl-forced-newline">
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+<A href="tutorials-how-tos.html" title="Tutorials & How-Tos">Tutorials & How-Tos</A><BR class="atl-forced-newline">
+<A href="configuration.html" title="Configuration">Configuration</A><BR class="atl-forced-newline">
+<A href="http://sling.apache.org/apidocs/sling6/index.html" class="external-link" rel="nofollow">API docs</A><BR class="atl-forced-newline">
+<A href="http://s.apache.org/sling.wiki" class="external-link" rel="nofollow">Wiki</A><BR class="atl-forced-newline">
+<A href="http://s.apache.org/sling.faq" class="external-link" rel="nofollow">FAQ</A><BR class="atl-forced-newline"></P>
+
+<P><B>Project info</B><BR class="atl-forced-newline">
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+<A href="http://www.apache.org/foundation/buy_stuff.html" class="external-link" rel="nofollow">Buy Stuff</A></P>
+
+
+ <IFRAME src="http://www.apache.org/ads/button.html" style="border-width:0; float: left" frameborder="0" scrolling="no" width="135" height="135"></IFRAME>
+ <P style="height: 135px"></P>
+ </DIV>
+ <DIV class="main">
+ <DIV class="breadcrump" style="font-size: 80%;">
+<A href="apache-sling.html" title="Apache Sling Website">Apache Sling Website</A> > <A href="apache-sling.html" title="Apache Sling">Apache Sling</A> > <A href="old-stuff.html" title="Old Stuff">Old Stuff</A> > <A href="" title="Request Processing">Request Processing</A>
+ </DIV>
+<H1><A name="RequestProcessing-HTTPRequestProcessing"></A>HTTP Request Processing</H1>
+
+<DIV class="panelMacro"><TABLE class="noteMacro"><COLGROUP><COL width="24"><COL></COLGROUP><TR><TD valign="top"><IMG src="https://cwiki.apache.org/confluence/images/icons/emoticons/warning.gif" width="16" height="16" align="absmiddle" alt="" border="0"></TD><TD><B>Page Status</B><BR>2008-02-13: this page is <B>out of sync</B> with the current codebase, needs to be reviewed and updated.</TD></TR></TABLE></DIV>
+
+<P>One of the core problems towards understanding how Sling works is knowing how a Client Request is processed by Sling. This page describes the flow of processing requests inside Sling.</P>
+
+
+<H2><A name="RequestProcessing-CoreRequestProcessing"></A>Core Request Processing</H2>
+
+
+<P>The HTTP request enters Sling in the <TT>org.apache.sling.core.ComponentRequestHandlerImpl.service(ServletRequest req, ServletResponse res)</TT> method as the <TT>ComponentRequestHandlerImpl</TT> is registered as the Servlet handling HTTP requests. This method sets up the initial <TT>ComponentRequest</TT> and <TT>ComponentResponse</TT> objects and hands the request over to the first <TT>ComponentFilterChain</TT>. This first filter chain calls all <TT>ComponentFilter</TT> instances registered as request level filters. After processing all filters in the request level filter chain, the request is handed over to the second <TT>ComponentFilterChain</TT> which calls all <TT>ComponentFilter</TT> instances registered as component level filters. At the end of the second filter chain the <TT>service</TT> method of the actual <TT>Component</TT> to which the request resolved is called.</P>
+
+<P>As the component is now processing the request, it may decide to dispatch the request to some other content such as for example a paragraph system or navigation component. To do this, the component will call the <TT>RequestDispatcher.include</TT> method. If the request dispatcher dispatches to a <TT>Content</TT> object Sling will hand the dispatch request over to the component level filter chain, which at the end will call the <TT>service</TT> method for the <TT>Content</TT> object to dispatched to. This process may be repeated at the component's discretion only limited by processing resources such as available memory.</P>
+
+
+<P>As can be seen Sling itself is absed on the Component API <TT>ComponentFilter</TT> mechanism. As such Sling provides and uses the following filters in the Sling Core bundle:</P>
+
+<TABLE class="wiki-table" cellpadding="0" cellspacing="0" border="0"><TR><TH><TR><TH colspan="2" class="confluenceTh"> Request Level Filters </TH></TR></TH></TR><TR class="table-odd"><TD><TR><TD class="confluenceTd"> <TT>ErrorHandlerFilter</TT> </TD><TD class="confluenceTd"> Handles exceptions thrown while processing the request as well implements the <TT>ComponentResponse.sendError()</TT> method </TD></TR></TD></TR><TR class="table-even"><TD><TR><TD class="confluenceTd"> <TT>AuthenticationFilter</TT> </TD><TD class="confluenceTd"> Implements authentication for the request and provides the JCR Session of the request </TD></TR></TD></TR><TR class="table-odd"><TD><TR><TD class="confluenceTd"> <TT>BurstCacheFilter</TT> </TD><TD class="confluenceTd"> Checks whether the request may be handled by cached response data </TD></TR></TD></TR><TR class="table-even"><TD><TR><TD class="confluenceTd"> <TT>LocaleResolverFilter</TT> </TD><TD class="confluenceTd"> Provides information on the
<TT>Locale</TT> to be used for request processing. This filter implements the <TT>ComponentRequest.getLocale()</TT> method </TD></TR></TD></TR><TR class="table-odd"><TD><TR><TD class="confluenceTd"> <TT>ThemeResolverFilter</TT> </TD><TD class="confluenceTd"> Provides the <TT>Theme</TT> for the request. The theme is provided as a request attribute </TD></TR></TD></TR><TR class="table-even"><TD><TR><TD class="confluenceTd"> <TT>URLMapperFilter</TT> </TD><TD class="confluenceTd"> Resolves the request URL to a JCR Node which may be mapped into a <TT>Content</TT> object </TD></TR></TD></TR><TR class="table-odd"><TD><TR><TD class="confluenceTd"> <TT>ZipFilter</TT> </TD><TD class="confluenceTd"> Sample filter showing how the request response might be compressed according to the <EM>Accept-Encoding</EM> request header. This filter is not enabled by default. </TD></TR></TD></TR></TABLE>
+
+
+
+<P>Deducing from these lists of filters, the actual request processing can be refined into the following steps:</P>
+
+<OL>
+ <LI>Extract user authentication information and acquire the JCR session to access content. If the request has no user authentication data the such data may be requested from the user (for example by sending a HTTP 401 status) or an anonymous repository session might be acquired.</LI>
+ <LI>Check whether the request may be handled by data stored in the cache. If the request is cacheable and a cache entry exists for the request URL, the request data is returned to the client and request processing may terminate. Otherwise request processing will continue and optionally ensure that any response data is entered into the cache. Of course, if the request is not cacheable, for example because there are request parameters, or if any of the <TT>Component</TT> instances called during request processing decide to signal non-cacheability for whatever reason, the response data will of course not cached.</LI>
+ <LI>Extract the <TT>java.util.Locale</TT> from the request such that further processing may use properly translated messages. By default, the locale of the underlying Servlet request is used as the request locale. Other possibilities would be to use special cookies or some locale encoding in the path.</LI>
+ <LI>Find the theme (or skin) to use to render the response. This step will add a <TT>org.apache.sling.theme.Theme</TT> object as a request parameter, which may be used by {{Component}}s to decide on specific rendering. For example, the theme may encapsulate information on the CSS to use for responses rendered as HTML.</LI>
+ <LI>Resolve the request URL into a <TT>Content</TT> object.</LI>
+</OL>
+
+
+
+<P>The default request level filter chain setup ends with finding the <TT>Content</TT> object requested by the request URL. After having found this object, the request is handed over to the component level filter chain, which is concerned with handling filtering on a single <TT>Content</TT> instance. As such, the component level filter chain is used for each <TT>Content</TT> object which is to be serviced either on behalf of the HTTP request or on behalf of request dispatcher. Thus the component level filter chain will generally called multiple times during a single request.</P>
+
+
+<TABLE class="wiki-table" cellpadding="0" cellspacing="0" border="0"><TR><TH><TR><TH colspan="2" class="confluenceTh"> Component Level Filters </TH></TR></TH></TR><TR class="table-odd"><TD><TR><TD class="confluenceTd"> <TT>CacheFilter</TT> </TD><TD class="confluenceTd"> Checks whether the request to the current <TT>Content</TT> object may be handled by cached response data </TD></TR></TD></TR><TR class="table-even"><TD><TR><TD class="confluenceTd"> <TT>ComponentResolverFilter</TT> </TD><TD class="confluenceTd"> Resolves the component ID returned by the <TT>Content.getComponentId()</TT> method into a <TT>Component</TT> instances, which will be called to service the request </TD></TR></TD></TR></TABLE>
+
+<P>Again, deducing from the list of filters, the following steps are taking to service a given <TT>Content</TT> object:</P>
+
+<OL>
+ <LI>Check whether the <TT>Content</TT> object processing may be handled from the cache. Same as with request level cache handling, a cache entry may exist for a single <TT>Content</TT> instance depending on whether the request is cacheable at all and on whether a cache entry exists. If a cache entry exists and may be used, the response data is simply spooled into the response and component level processing terminates for the <TT>Content</TT> object. Otherwise processing continues and may optionally lead to a new cache entry for the <TT>Content</TT> object to be reused later.</LI>
+ <LI>Resolve the component ID returned by the <TT>Content.getComponentId()</TT> method into a <TT>Component</TT> object. Of course it is an error, if the component ID cannot be mapped into a <TT>Component</TT> object.</LI>
+</OL>
+
+
+<P>After resolving the <TT>Component</TT> object default component filter chain terminates and control is handed over to the <TT>service</TT> method of the <TT>Component</TT> object resolved in the last step. At the discretion of the component request dispatchers may now be acquired to render other <TT>Content</TT> objects. In this case the component level filter chain is simply kicked of again resulting in the <TT>service</TT> method of another <TT>Component</TT> being called. And so forth.</P>
+
+
+
+<H2><A name="RequestProcessing-ResolvingContent"></A>Resolving Content</H2>
+
+<P>As we have seen, the last step in the request level filter chain is the resolution of the request URL into a <TT>Content</TT> object. The URL Mapper Filter implementing this resolution uses an instance of the <TT>org.apache.sling.content.ContentMapper</TT> interface which is acquired by calling the <TT>org.apache.sling.content.jcr.JcrContentManagerFactory</TT> with the repository session acquired by the authentication filter.</P>
+
+<P>The URL Mapper filter then tries to apply fixed mappings from request URL to destination paths to support shortcut URLs. For example the root path <TT>/</TT> may be mapped into the default landing page at <TT>/default/home</TT>. The list of such mappings is configurable through the Configuration Admin Service.</P>
+
+<P>Next the URL Mapper tries to apply prefix matching patterns. A list of patterns is iterated checking whether the prefix applies and, if so, replacing the prefix with another prefix and trying to resolve the result. This functionality enables relocation of a subtree of the repository. For example, all requests whose prefix is <TT>/here</TT> might be remapped with the new prefix <TT>/content/there</TT>. The result of this remapping is then resolved.</P>
+
+<P>Resolution (currently) takes place on the last path segment of the request URL containing at least one dot. Parts of that segment are cut off after dots until no more dots exist in the URL. For each resulting substring, the <TT>ContentManager.load(String)</TT> method is called. This processing terminates if a <TT>Content</TT> object is found or if there is nothing to cut off any more.</P>
+
+<P>This resolution is very simple and straight forwards. Future development may add support for the following features:</P>
+
+<UL>
+ <LI><B>Vanity URLs</B> - Map the request URL according to the <TT>Host</TT> request header.</LI>
+ <LI><B>Dynamic Mapping</B> - Add support for a set of variables in path and/or prefix mapping. For example, a prefix mapping may contain the string <TT>/content/${lang}/${user</TT>} resulting in resolving a prefix according to the language of the current locale and the name of the authenticated used.</LI>
+</UL>
+
+
+
+
+<H2><A name="RequestProcessing-RegisteringComponents"></A>Registering Components</H2>
+
+
+<P>The last step of the component level filter chain is resolving the <TT>Component</TT> from the component ID of the <TT>Content</TT> object. Sling implements this resolution by making use of the OSGi service registry. That is, each component is to be registered as a service with the name <TT>org.apache.sling.component.Component</TT>. The <TT>ComponentResolverFilter</TT> is listening for these components and registers them internally in a map indexed by the IDs of the component as returned by the <TT>Component.getId()</TT> method.</P>
+
+<P>When a component has to be resolved, the component ID returned by the <TT>Content</TT> object is simply looked up in the component map. If found, that component is used. Otherwise a fall back algorithm is applied which is described on the <A href="default-mapping-and-rendering.html" title="Default Mapping and Rendering">Default Content Mapping and Request Rendering</A> page.</P>
+
+
+
+<H2><A name="RequestProcessing-ReqisteringFilters"></A>Reqistering Filters</H2>
+
+<P>Just as <TT>Component</TT> instances used by Sling are expected to be registered as OSGi services, the {{ComponentFilter}}s to be <BR>
+used have to be registered as services under the name <TT>org.apache.sling.component.ComponentFilter</TT>. Sling picks up all registered component filters and adds them to the respective filter chains.</P>
+
+<P>Service properties set upon registration of the filter define the chain to which the filter belongs and the order in which the filters should be processed:</P>
+
+<DIV class="table-wrap">
+<TABLE class="confluenceTable"><TBODY>
+<TR>
+<TH class="confluenceTh"> Property </TH>
+<TH class="confluenceTh"> Description </TH>
+</TR>
+<TR>
+<TD class="confluenceTd"> <TT>filter.scope</TT> </TD>
+<TD class="confluenceTd"> Defines the chain to which the filter is added. Supported values are <TT>component</TT> for component level filters and <TT>request</TT> for request level filters. If this property is missing or set to an unknown value the filter is added to the request level filter chain. </TD>
+</TR>
+<TR>
+<TD class="confluenceTd"> <TT>filter.order</TT> </TD>
+<TD class="confluenceTd"> Defines the weight of the filter to resolve the processing order. This property must be an <TT>java.lang.Integer</TT>. If not set or not an <TT>Integer</TT> the order defaults to <TT>Integer.MAX_VALUE</TT>. The lower the order number the earlier in the filter chain will the filter be inserted. If two filters are registered with the same order value, the filter with the lower <TT>service.id</TT> value is called first. </TD>
+</TR>
+</TBODY></TABLE>
+</DIV>
+
+
+
+
+<H2><A name="RequestProcessing-ContentisaJavaObject"></A>Content is a Java Object</H2>
+
+<P>It is crucial to understand that <TT>Content</TT> is an interface and the request processor of Sling does not actually care, how the <TT>Content</TT> instance comes to live as long as the is such an object and there is a <TT>Component</TT> instance capable of servicing the <TT>Content</TT> object.</P>
+
+<P>By default Sling uses the <EM>URL Mapper</EM> to resolve the request URL into a <TT>Content</TT> object. When a <TT>Component</TT> is tasked with servicing a <TT>Content</TT> object it usually uses the <TT>ComponentRequestDispatcher</TT> to ask Sling to service another content object generally identified by a (relative or absolute) path to a JCR Repository Node from which the <TT>Content</TT> object is loaded.</P>
+
+<P>But instead of having Sling resolve a path into a <TT>Content</TT> object the component may just as well create a <TT>Content</TT> object and hand it over to the <TT>ComponentRequestDispatcher</TT> for service. Consider a request which is handled by a <TT>PageComponent</TT>. This component has to draw a navigation tree somewhere in the response. So the component could of course insist on having a <TT>navigation</TT> child node to dispatch rendering to as follows:</P>
+
+
+<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
+<PRE class="code-java">
+RequestDispatcher rd = request.getRequestDispatcher(<SPAN class="code-quote">"navigation"</SPAN>);
+rd.include(request, response);
+</PRE>
+</DIV></DIV>
+
+
+<P>What happens, though, if there is no <TT>navigation</TT> child node ? Probably, the request will fail with some error status. Of course the component could be more clever and do:</P>
+
+
+<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
+<PRE class="code-java">
+Content navigation = request.getContent(<SPAN class="code-quote">"navigation"</SPAN>);
+<SPAN class="code-keyword">if</SPAN> (navigation != <SPAN class="code-keyword">null</SPAN>) {
+ RequestDispatcher rd = request.getRequestDispatcher(navigation);
+ rd.include(request, response);
+}
+</PRE>
+</DIV></DIV>
+
+
+<P>Still, if the <TT>navigation</TT> child node does not exist, there is no navigation drawn; at least there will be now error. Since Sling does not actually care, how a <TT>Content</TT> object comes to live, the component could do the following:</P>
+
+
+<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
+<PRE class="code-java">
+Content navigation = <SPAN class="code-keyword">new</SPAN> Content() {
+ <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> getPath() {
+ <SPAN class="code-keyword">return</SPAN> request.getContent().getPath() + <SPAN class="code-quote">"/navigation"</SPAN>;
+ }
+ <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> getComponentId() {
+ <SPAN class="code-keyword">return</SPAN> NavigationComponent.getClass().getName();
+ }
+}
+
+RequestDispatcher rd = request.getRequestDispatcher(navigation);
+rd.include(request, response);
+</PRE>
+</DIV></DIV>
+
+
+<P>Of course, the page component now has to have knowledge about the actual <TT>Component</TT> to use.</P>
+
+
+<P>Finally, as a further enhancement, the Component might even decide to first check for a <TT>navigation</TT> child node. If such a node does not exist the navigation <TT>Content</TT> object is just created:</P>
+
+
+<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
+<PRE class="code-java">
+Content navigation = request.getContent(<SPAN class="code-quote">"navigation"</SPAN>);
+<SPAN class="code-keyword">if</SPAN> (navigation == <SPAN class="code-keyword">null</SPAN>) {
+ navigation = <SPAN class="code-keyword">new</SPAN> Content() {
+ <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> getPath() {
+ <SPAN class="code-keyword">return</SPAN> request.getContent().getPath() + <SPAN class="code-quote">"/navigation"</SPAN>;
+ }
+ <SPAN class="code-keyword">public</SPAN> <SPAN class="code-object">String</SPAN> getComponentId() {
+ <SPAN class="code-keyword">return</SPAN> NavigationComponent.getClass().getName();
+ }
+ }
+}
+
+RequestDispatcher rd = request.getRequestDispatcher(navigation);
+rd.include(request, response);
+</PRE>
+</DIV></DIV>
+
+
+<P>This could for example be used to fall back to a default navigation setup while providing for specialized navigation configuration in an optional <TT>navigation</TT> child node.</P>
+ <DIV class="timestamp" style="margin-top: 30px; font-size: 80%; text-align: right;">
+Last modified by mykee on 2008-02-13 07:10:28.0
+ </DIV>
+ <DIV class="trademarkFooter">
+Apache Sling, Sling, Apache, the Apache feather logo, and the Apache Sling project logo are trademarks of The Apache Software Foundation. All other marks mentioned may be trademarks or registered trademarks of their respective owners.
+ </DIV>
+ </DIV>
+ </BODY>
+</HTML>
+
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--- sling/site/trunk/content/site/resources.html (added)
+++ sling/site/trunk/content/site/resources.html Wed Dec 12 09:13:50 2012
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+
+<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+<HTML>
+ <HEAD>
+ <TITLE>Apache Sling - Resources</TITLE>
+ <LINK rel="stylesheet" href="http://sling.apache.org/site/media.data/site.css" type="text/css" media="all">
+ <LINK rel="icon" href="http://sling.apache.org/site/media.data/favicon.ico">
+ <META http-equiv="Content-Type" content="text/html;charset=UTF-8">
+ </HEAD>
+ <BODY>
+ <DIV class="title">
+ <DIV class="logo">
+ <A href="http://sling.apache.org/site/index.html">
+ <IMG border="0" alt="Apache Sling" src="http://sling.apache.org/site/media.data/logo.png">
+ </A>
+ </DIV>
+ <DIV class="header">
+ <A href="http://www.apache.org/">
+ <IMG border="0" alt="Apache" src="http://sling.apache.org/site/media.data/apache.png">
+ </A>
+ </DIV>
+ </DIV>
+ <DIV class="menu">
+<P><B>Documentation</B><BR class="atl-forced-newline">
+<A href="getting-started.html" title="Getting Started">Getting Started</A><BR class="atl-forced-newline">
+<A href="the-sling-engine.html" title="The Sling Engine">The Sling Engine</A><BR class="atl-forced-newline">
+<A href="development.html" title="Development">Development</A><BR class="atl-forced-newline">
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+ </DIV>
+ <DIV class="main">
+ <DIV class="breadcrump" style="font-size: 80%;">
+<A href="apache-sling.html" title="Apache Sling Website">Apache Sling Website</A> > <A href="apache-sling.html" title="Apache Sling">Apache Sling</A> > <A href="documentation.html" title="Documentation">Documentation</A> > <A href="the-sling-engine.html" title="The Sling Engine">The Sling Engine</A> > <A href="" title="Resources">Resources</A>
+ </DIV>
+<H1><A name="Resources-Resources"></A>Resources</H1>
+
+<DIV>
+<UL>
+ <LI><A href="#Resources-WhatisaResource">What is a Resource</A></LI>
+ <LI><A href="#Resources-HowtogetaResource">How to get a Resource</A></LI>
+<UL>
+ <LI><A href="#Resources-AbsolutePathMapping">Absolute Path Mapping</A></LI>
+ <LI><A href="#Resources-RelativePathResolution">Relative Path Resolution</A></LI>
+ <LI><A href="#Resources-QueryingResources">Querying Resources</A></LI>
+</UL>
+ <LI><A href="#Resources-ProvidingResources">Providing Resources</A></LI>
+<UL>
+ <LI><A href="#Resources-JCRbasedResources">JCR-based Resources</A></LI>
+ <LI><A href="#Resources-BundlebasedResources">Bundle-based Resources</A></LI>
+ <LI><A href="#Resources-ServletResources">Servlet Resources</A></LI>
+ <LI><A href="#Resources-FileSystemResources">File System Resources</A></LI>
+</UL>
+ <LI><A href="#Resources-Wrap%252FDecorateResources">Wrap/Decorate Resources</A></LI>
+</UL></DIV>
+
+<H2><A name="Resources-WhatisaResource"></A>What is a Resource</H2>
+
+<P>The Resource is one of the central parts of Sling. Extending from JCR's <EM>Everything is Content</EM>, Sling assumes <EM>Everthing is a Resource</EM>. Thus Sling is maintaining a virtual tree of resources, which is a merger of the actual contents in the JCR Repository and resources provided by so called resource providers. By doing this Sling fits very well in the paradigma of the REST architecture.</P>
+
+<H2><A name="Resources-HowtogetaResource"></A>How to get a Resource</H2>
+
+<P>To get at Resources, you need a <TT>ResourceResolver</TT>. This interface defines four kinds of methods to access resources:</P>
+<UL>
+ <LI>Absolute Path Mapping Resource Resolution: The <TT>resolve(HttpServletRequest, String)</TT> and <TT>resolve(String)</TT> methods are called to apply some implementation specific path matching algorithm to find a Resource. These methods are mainly used to map external paths - such as path components of request URLs - to Resources. To support creating external paths usable in an URL a third method <TT>map(String)</TT> is defined, which allows for round-tripping.</LI>
+ <LI>Absolute or Relative Path Resolution (including search path): The <TT>getResource(String path)</TT> and <TT>getResource(Resource base, String path)</TT> methods may be used to access a resource with an absolute path directly. If it can't be found the path is assumed to be relative and the search path retrieved from <TT>getSearchPath()</TT> is used to retrieve the resource. This mechanism is similar to resolving a programm with the <TT>PATH</TT> environment variable in your favourite operating system.</LI>
+ <LI>Resource Enumeration: To enumerate resources and thus iterate the resource tree, the <TT>listChildren(Resource)</TT> method may be used. This method returns an <TT>Iterator<Resource></TT> listing all resources whose path prefix is the path of the given Resource. This method will of course also cross boundaries of registered <TT>ResourceProvider</TT> instances to enable iterating the complete resource tree.</LI>
+ <LI>Resource Querying: Querying resources is currently only supported for JCR Resources through the <TT>findResources(String query, String language)</TT> and <TT>queryResources(String query, String language)</TT> methods. For more information see the section on <A href="#Resources-QueryingResources">Querying_Resources</A> below.</LI>
+</UL>
+
+
+<H3><A name="Resources-AbsolutePathMapping"></A>Absolute Path Mapping</H3>
+
+<P>As has been said, the absolute path mapping methods <TT>resolve(HttpServletRequest, String)</TT> and <TT>resolve(String)</TT> apply some implementation specific path matching algorithm to find a Resource. The difference between the two methods is that the former may take more properties of the <TT>HttpServletRequest</TT> into account when resolving the Resoure, while the latter just has an absolute path to work on.</P>
+
+<P>The general algorithm of the two methods is as follows:</P>
+<OL>
+ <LI>Call <TT>HttpServletRequest.getScheme(), .getServerName(), getServerPort</TT> to get an absolute path out of the request URL: [scheme]/[host].[port][path] (<TT>resolve(HttpServletRequest, String)</TT> method only, which)</LI>
+ <LI>Check whether any virtual path matches the absolute path. If such a match exists, the next step is entered with the match.</LI>
+ <LI>Apply a list of mappings in order to create a mapped path. The first mapped path resolving to a Resource is assumed success and the Resource found is returned.</LI>
+ <LI>If no mapping created a mapped path addressing an existing Resource, the method fails and returns:</LI>
+</OL>
+
+
+<UL>
+ <LI>The <TT>resolve(String)</TT> and <TT>resolve(HttpServletRequest,String)</TT> methods return a <TT>NonExistingResource</TT></LI>
+ <LI>The <TT>getResource(String path)</TT> and <TT>getResource(Resource base, String path)</TT> methods return null</LI>
+</UL>
+
+
+<P>The virtual path mapping may be used to create shortcut URLs for otherwise long and complicated URLs. An example of such an URL might be the main administrative page of a CMS system. So, administrators may access the root of the web application and directed to the main administrative page.</P>
+
+<P>The path mapping functionality may be used to hide internal resource organization from the request URL space. For example to better control the structure of your repository, you might decide to store all accessible data inside a <TT>/content</TT> subtree. To hide this fact from the users, a mapping may be defined to prefix all incoming paths with <TT>/content</TT> to get at the actual Resource.</P>
+
+<P>The <TT>map(String)</TT> applies the path mapping algorithm in the reverse order. That is, first the path mappings are reversed and then any virtual mappings are checked. So, a path <TT>/content/sample</TT> might be mapped <TT>/sample</TT> to revers the <TT>/content</TT> prefixing. Or the main administrative page - say <TT>/system/admin/main.html</TT> - may be mapped to the virtual URL <TT>/</TT>.</P>
+
+<H3><A name="Resources-RelativePathResolution"></A>Relative Path Resolution</H3>
+
+<P>Sometimes it is required to resolve relative paths to Resources. An example of such a use case is Script and Servlet resolution which starts with a relative path consisting of the Resource type, optional selectors and the request extension or method name. By scanning a search path for these relative paths a system provided Resource may be overwritten with some user defined implementation.</P>
+
+<P>Consider for example, the system would provide a Servlet to render Resources of type <TT>nt:file</TT>. This Servlet would be registered under the path <TT>/libs/nt/file/html</TT>. For a certain web application, this default HTML rendering might not be appropriate, so a Script is created as <TT>/apps/nt/file/html.jsp</TT> with a customized HTML rendering. By defining the search path to be <EM>[</EM> <TT><EM>/apps</EM></TT><EM>,</EM> <TT><EM>/libs</EM></TT> <EM>]</EM> the Servlet resolver would call the <TT>ResourceResolver.getResource(String)</TT> method with the relative path <TT>nt/file/html</TT> and be provided with the first matching resource - <TT>/apps/nt/file/html.jsp</TT> in this example.</P>
+
+<P>Of course the search path is not used for absolute path arguments.</P>
+
+<H3><A name="Resources-QueryingResources"></A>Querying Resources</H3>
+
+<P>For convenience the <TT>ResourceResolver</TT> provides two Resource querying methods <TT>findResources</TT> and <TT>queryResources</TT> both methods take as arguments a JCR query string and a query language name. These parameters match the parameter definition of the <TT>QueryManager.createQuery(String statement, String language)</TT> method of the JCR API.</P>
+
+<P>The return value of these two methods differ in the use case:</P>
+<UL>
+ <LI><TT>findResources</TT> returns an <TT>Iteratory<Resource></TT> of all Resources matching the query. This method is comparable to calling <TT>getNodes()</TT> on the <TT>QueryResult</TT> returned from executing the JCR query.</LI>
+ <LI><TT>queryResources</TT> returns an <TT>Iterator<Map<String, Object>></TT>. Each entry in the iterator is a <TT>Map<String, Object</TT> representing a JCR result <TT>Row</TT> in the <TT>RowIterator</TT> returned from executing the JCR query. The map is indexed by the column name and the value of each entry is the value of the named column as a Java Object.</LI>
+</UL>
+
+
+<P>These methods are convenience methods to more easily post queries to the repository and to handle results in very straight forward way using only standard Java functionality.</P>
+
+<P>Please note, that Resource querying is currently only supported for repository based Resources. These query methods are not reflected in the <TT>ResourceProvider</TT> interface used to inject non-repository Resources into the Resource tree.</P>
+
+<H2><A name="Resources-ProvidingResources"></A>Providing Resources</H2>
+
+<P>The virtual Resource tree to which the the Resource accessor methods <TT>resolve</TT> and <TT>getResource</TT> provide access is implemented by a collection of registered <TT>ResourceProvider</TT> instances. The main Resource provider is of course the repository based <TT>JcrResourceProvider</TT> which supports Node and Property based resources. This Resource provider is always available in Sling. Further Resource providers may or may not exist.</P>
+
+<P>Each Resource provider is registered as an OSGi service with a required service registration property <TT>provider.roots</TT>. This is a multi-value String property listing the absolute paths Resource tree entries serving as roots to provided subtrees. For example, if a Resource provider is registered with the service registration property <TT>provider.roots</TT> set to <EM>/some/root</EM>, all paths starting with <TT>/some/root</TT> are first looked up in the given Resource Provider.</P>
+
+<P>When looking up a Resource in the registered Resource providers, the <TT>ResourceResolver</TT> applies a longest prefix matching algorithm to find the best match. For example consider three Resource provider registered as follows:</P>
+<UL>
+ <LI>JCR Resource provider as <TT>/</TT></LI>
+ <LI>Resource provider R1 as <TT>/some</TT></LI>
+ <LI>Resource provider R2 as <TT>/some/path</TT></LI>
+</UL>
+
+
+<P>When accessing a Resource with path <TT>/some/path/resource</TT> the Resource provider <EM>R2</EM> is first asked. If that cannot provide the resource, Resource provider <EM>R1</EM> is asked and finally the JCR Resource provider is asked. The first Resource provider having a Resource with the requested path will be used.</P>
+
+<H3><A name="Resources-JCRbasedResources"></A>JCR-based Resources</H3>
+
+<P>JCR-based Resources are provided with the default <TT>JcrResourceProvider</TT>. This Resource provider is always available and is always asked last. That is Resources provided by other Resource providers may never be overruled by repository based Resources.</P>
+
+<H3><A name="Resources-BundlebasedResources"></A>Bundle-based Resources</H3>
+
+<P>Resources may by provided by OSGi bundles. Providing bundles have a Bundle manifest header <TT>Sling-Bundle-Resources</TT> containing a list of absolute paths provided by the bundle. The path are separated by comma or whitespace (SP, TAB, VTAB, CR, LF).</P>
+
+<P>The <TT>BundleResourceProvider</TT> supporting bundle-based Resources provides directories as Resources of type <TT>nt:folder</TT> and files as Resources of type <TT>nt:file</TT>. This matches the default primary node types intended to be used for directories and files in JCR repositories. For details see <A href="bundle-resources-extensionsbundleresource.html" title="Bundle Resources (extensions.bundleresource)">Bundle Resource.</A></P>
+
+<H3><A name="Resources-ServletResources"></A>Servlet Resources</H3>
+
+<P>Servlet Resources are registered by the Servlet Resolver bundle for Servlets registered as OSGi services. See <A href="servlets.html" title="Servlets">Servlet Resolution</A> for information on how Servlet Resources are provided.</P>
+
+<H3><A name="Resources-FileSystemResources"></A>File System Resources</H3>
+
+<P>The Filesystem Resource Provider provides access to the operating system's filesystem through the Sling ResourceResolver. Multiple locations may be mapped into the resource tree by configuring the filesystem location and the resource tree root path for each location to be mapped. For details see <A href="accessing-filesystem-resources-extensionsfsresource.html" title="Accessing Filesystem Resources (extensions.fsresource)">File System Resources</A>.</P>
+
+<H2><A name="Resources-Wrap%2FDecorateResources"></A>Wrap/Decorate Resources</H2>
+
+<P>The Sling API provides an easy way to wrap or decorate a resource before returning. Details see <A href="wrap-or-decorate-resources.html" title="Wrap or Decorate Resources">Wrap or Decorate Resources</A>.</P>
+ <DIV class="timestamp" style="margin-top: 30px; font-size: 80%; text-align: right;">
+Last modified by mykee on 2010-08-25 03:33:22.0
+ </DIV>
+ <DIV class="trademarkFooter">
+Apache Sling, Sling, Apache, the Apache feather logo, and the Apache Sling project logo are trademarks of The Apache Software Foundation. All other marks mentioned may be trademarks or registered trademarks of their respective owners.
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