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Posted to dev@tapestry.apache.org by bu...@apache.org on 2015/11/11 13:19:45 UTC
svn commit: r972093 - in /websites/production/tapestry/content:
cache/main.pageCache page-life-cycle.html request-processing.html
Author: buildbot
Date: Wed Nov 11 12:19:45 2015
New Revision: 972093
Log:
Production update by buildbot for tapestry
Modified:
websites/production/tapestry/content/cache/main.pageCache
websites/production/tapestry/content/page-life-cycle.html
websites/production/tapestry/content/request-processing.html
Modified: websites/production/tapestry/content/cache/main.pageCache
==============================================================================
Binary files - no diff available.
Modified: websites/production/tapestry/content/page-life-cycle.html
==============================================================================
--- websites/production/tapestry/content/page-life-cycle.html (original)
+++ websites/production/tapestry/content/page-life-cycle.html Wed Nov 11 12:19:45 2015
@@ -125,7 +125,7 @@
</div>
</li></ul>
-</div><p>In Tapestry, you are free to develop your presentation objects, page and components classes, as ordinary objects, complete with instance variables and so forth.</p><p>This is somewhat revolutionary in terms of web development in Java. Using traditional servlets, or Struts, your presentation objects (Servlets, or Struts Actions, or the equivalent in other frameworks) are <em>stateless singletons</em>. That is, a <em>single</em> instance is created, and all incoming requests are threaded through that single instance.</p><p>Because multiple requests are handled by many different threads, this means that the single instance's variable are useless ... any value written into an instance variable would immediately be overwritten by a different thread. Thus, it is necessary to use the Servlet API's HttpServletRequest object to store per-request data, and the HttpSession object to store data between requests.</p><p>Tapestry takes a very different approach.</p><p>In Tapestry, each pa
ge is a singleton, but with a <em>per thread</em> map of field names & values that Tapestry invisibly manages for you.</p><p>With this approach, all the difficult, ugly issues related to multi-threading go by the wayside. Instead, familiar, simple coding practices (using ordinary methods and fields) can be used.</p><div class="confluence-information-macro confluence-information-macro-information"><span class="aui-icon aui-icon-small aui-iconfont-info confluence-information-macro-icon"></span><div class="confluence-information-macro-body"><p>Tapestry 5.0 and 5.1 used page pooling, rather than a singleton page with a per_thread map, to achieve the same effect.</p></div></div><h2 id="PageLifeCycle-PageLifeCycleMethods">Page Life Cycle Methods</h2><p>There are a few situations where it is useful for a component to perform some operations, usually some kind of initialization or caching, based on the life cycle of the page.</p><p>The page life cycle is quite simple. When first needed,
a page is loaded. Loading a page involves instantiating the components of the page and connecting them together.</p><p>Once a page is loaded, it is <em>attached</em> to the current request. Remember that there will be many threads, each handling its own request to the same page.</p><p>At the end of a request, after a response has been sent to the client, the page is <em>detached</em> from the request. This is a chance to perform any cleanup needed for the page.</p><p>As with <a href="component-rendering.html">component rendering</a>, you have the ability to make your components "aware" of these events by identifying methods to be invoked.</p><p>Page life cycle methods should take no parameters and return void.</p><p>You have the choice of attaching an annotation to a method, or simply using the method naming conventions:</p><div class="table-wrap"><table class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1" class="confluenceTh"><p>Annotation</p></th><th colspan="1" rowspa
n="1" class="confluenceTh"><p>Method Name</p></th><th colspan="1" rowspan="1" class="confluenceTh"><p>When Called</p></th></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageLoaded.html">PageLoaded</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageLoaded()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>After the page is fully loaded</p></td></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageAttached.html">PageAttached</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageAttached()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>After the page is attached to the request.</p></td></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry
.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageDetached.html">PageDetached</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageDetached()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>AFter the page is detached from the request.</p></td></tr></tbody></table></div><h2 id="PageLifeCycle-ComparisontoJavaServerPages">Comparison to JavaServer Pages</h2><p>JSPs also act as singletons. However, the individual JSP tags are pooled.</p><p>This is one of the areas where Tapestry can significantly outperform JSPs. Much of the code inside a compiled JSP class concerns getting tags from a tag pool, configuring the properties of the tag instance, using the tag instance, then cleaning up the tag instance and putting it back in the pool.</p><p>The operations Tapestry does once per request are instead executed dozens or potentially hundreds of times (depending the complexity of the page, and if any nested loops occur).</p><p>Pooling JSP tags is simply t
he wrong granularity.</p><p>Tapestry can also take advantage of its more coarse grained caching to optimize how data moves, via parameters, between components. This means that Tapestry pages will actually speed up after they render the first time.</p><h2 id="PageLifeCycle-PagePoolConfiguration">Page Pool Configuration</h2><div class="confluence-information-macro confluence-information-macro-note"><span class="aui-icon aui-icon-small aui-iconfont-warning confluence-information-macro-icon"></span><div class="confluence-information-macro-body"><p>This related to versions of Tapestry prior to 5.2. Modern Tapestry uses an alternate approach that allows a single page instance to be shared across many request processing threads.</p></div></div><p>In Tapestry 5.0 and 5.1, a page pool is used to store page instances. The pool is "keyed" on the name of the page (such as "start") and the <em>locale</em> for the page (such as "en" or "fr").</p><p>Within each key, Tapestry tracks the number of p
age instances that have been created, as well as the number that are in use (currently attached to a request).</p><p>When a page is first accessed in a request, it is taken from the pool. Tapestry has some <a href="configuration.html">configuration values</a> that control the details of how and when page instances are created.</p><ul><li>If a free page instance is available, the page is marked in use and attached to the request.</li><li>If there are fewer page instances than the <em>soft limit</em>, then a new page instance is simply created and attached to the request.</li><li>If the soft limit has been reached, Tapestry will wait for a short period of time for a page instance to become available before creating a new page instance.</li><li>If the hard limit has been reached, Tapestry will throw an exception rather than create a new page instance.</li><li>Otherwise, Tapestry will create a new page instance.<br clear="none"> Thus a busy application will initially create pages up-to
the soft limit (which defaults to five page instances). If the application continues to be pounded with requests, it will slow its request processing, using the soft wait time in an attempt to reuse an existing page instance.</li></ul><p>A truly busy application will continue to create new page instances as needed until the hard limit is reached.</p><p>Remember that all these configuration values are per key: the combination of page name and locale. Thus even with a hard limit of 20, you may eventually find that Tapestry has created 20 start page instances for locale "en" <em>and</em> 20 start page instances for locale "fr" (if your application is configured to support both English and French). Likewise, you may have 20 instances for the start page, and 20 instances for the newaccount page.</p><p>Tapestry periodically checks its cache for page instances that have not been used recently (within a configurable window). Unused page instances are release to the garbage collector.</p><p
>The end result is that you have quite a degree of tuning control over the process. If memory is a limitation and throughput can be sacrificed, try lowering the soft and hard limit and increasing the soft wait.</p><p>If performance is absolute and you have lots of memory, then increase the soft and hard limit and reduce the soft wait. This encourages Tapestry to create more page instances and not wait as long to re-use existing instances.</p></div>
+</div><p>In Tapestry, you are free to develop your presentation objects, page and components classes, as ordinary objects, complete with instance variables and so forth.</p><p>This is somewhat revolutionary in terms of web development in Java. Using traditional servlets, or Struts, your presentation objects (Servlets, or Struts Actions, or the equivalent in other frameworks) are <em>stateless singletons</em>. That is, a <em>single</em> instance is created, and all incoming requests are threaded through that single instance.</p><p>Because multiple requests are handled by many different threads, this means that the single instance's variable are useless ... any value written into an instance variable would immediately be overwritten by a different thread. Thus, it is necessary to use the Servlet API's HttpServletRequest object to store per-request data, and the HttpSession object to store data between requests.</p><p>Tapestry takes a very different approach.</p><p>In Tapestry, each pa
ge is a singleton, but with a <em>per thread</em> map of field names & values that Tapestry invisibly manages for you.</p><p>With this approach, all the difficult, ugly issues related to multi-threading go by the wayside. Instead, familiar, simple coding practices (using ordinary methods and fields) can be used.</p><div class="confluence-information-macro confluence-information-macro-information"><span class="aui-icon aui-icon-small aui-iconfont-info confluence-information-macro-icon"></span><div class="confluence-information-macro-body"><p>Tapestry 5.0 and 5.1 used page pooling, rather than a singleton page with a per-thread map, to achieve the same effect.</p></div></div><h2 id="PageLifeCycle-PageLifeCycleMethods">Page Life Cycle Methods</h2><p>There are a few situations where it is useful for a component to perform some operations, usually some kind of initialization or caching, based on the life cycle of the page.</p><p>The page life cycle is quite simple. When first needed,
a page is loaded. Loading a page involves instantiating the components of the page and connecting them together.</p><p>Once a page is loaded, it is <em>attached</em> to the current request. Remember that there will be many threads, each handling its own request to the same page.</p><p>At the end of a request, after a response has been sent to the client, the page is <em>detached</em> from the request. This is a chance to perform any cleanup needed for the page.</p><p>As with <a href="component-rendering.html">component rendering</a>, you have the ability to make your components "aware" of these events by identifying methods to be invoked.</p><p>Page life cycle methods should take no parameters and return void.</p><p>You have the choice of attaching an annotation to a method, or simply using the method naming conventions:</p><div class="table-wrap"><table class="confluenceTable"><tbody><tr><th colspan="1" rowspan="1" class="confluenceTh"><p>Annotation</p></th><th colspan="1" rowspa
n="1" class="confluenceTh"><p>Method Name</p></th><th colspan="1" rowspan="1" class="confluenceTh"><p>When Called</p></th></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageLoaded.html">PageLoaded</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageLoaded()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>After the page is fully loaded</p></td></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageAttached.html">PageAttached</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageAttached()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>After the page is attached to the request.</p></td></tr><tr><td colspan="1" rowspan="1" class="confluenceTd"><p>@<a class="external-link" href="http://tapestry
.apache.org/current/apidocs/org/apache/tapestry5/annotations/PageDetached.html">PageDetached</a></p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>pageDetached()</p></td><td colspan="1" rowspan="1" class="confluenceTd"><p>AFter the page is detached from the request.</p></td></tr></tbody></table></div><h2 id="PageLifeCycle-ComparisontoJavaServerPages">Comparison to JavaServer Pages</h2><p>JSPs also act as singletons. However, the individual JSP tags are pooled.</p><p>This is one of the areas where Tapestry can significantly outperform JSPs. Much of the code inside a compiled JSP class concerns getting tags from a tag pool, configuring the properties of the tag instance, using the tag instance, then cleaning up the tag instance and putting it back in the pool.</p><p>The operations Tapestry does once per request are instead executed dozens or potentially hundreds of times (depending the complexity of the page, and if any nested loops occur).</p><p>Pooling JSP tags is simply t
he wrong granularity.</p><p>Tapestry can also take advantage of its more coarse grained caching to optimize how data moves, via parameters, between components. This means that Tapestry pages will actually speed up after they render the first time.</p><h2 id="PageLifeCycle-PagePoolConfiguration">Page Pool Configuration</h2><div class="confluence-information-macro confluence-information-macro-note"><span class="aui-icon aui-icon-small aui-iconfont-warning confluence-information-macro-icon"></span><div class="confluence-information-macro-body"><p>This related to versions of Tapestry prior to 5.2. Modern Tapestry uses an alternate approach that allows a single page instance to be shared across many request processing threads.</p></div></div><p>In Tapestry 5.0 and 5.1, a page pool is used to store page instances. The pool is "keyed" on the name of the page (such as "start") and the <em>locale</em> for the page (such as "en" or "fr").</p><p>Within each key, Tapestry tracks the number of p
age instances that have been created, as well as the number that are in use (currently attached to a request).</p><p>When a page is first accessed in a request, it is taken from the pool. Tapestry has some <a href="configuration.html">configuration values</a> that control the details of how and when page instances are created.</p><ul><li>If a free page instance is available, the page is marked in use and attached to the request.</li><li>If there are fewer page instances than the <em>soft limit</em>, then a new page instance is simply created and attached to the request.</li><li>If the soft limit has been reached, Tapestry will wait for a short period of time for a page instance to become available before creating a new page instance.</li><li>If the hard limit has been reached, Tapestry will throw an exception rather than create a new page instance.</li><li>Otherwise, Tapestry will create a new page instance.<br clear="none"> Thus a busy application will initially create pages up-to
the soft limit (which defaults to five page instances). If the application continues to be pounded with requests, it will slow its request processing, using the soft wait time in an attempt to reuse an existing page instance.</li></ul><p>A truly busy application will continue to create new page instances as needed until the hard limit is reached.</p><p>Remember that all these configuration values are per key: the combination of page name and locale. Thus even with a hard limit of 20, you may eventually find that Tapestry has created 20 start page instances for locale "en" <em>and</em> 20 start page instances for locale "fr" (if your application is configured to support both English and French). Likewise, you may have 20 instances for the start page, and 20 instances for the newaccount page.</p><p>Tapestry periodically checks its cache for page instances that have not been used recently (within a configurable window). Unused page instances are release to the garbage collector.</p><p
>The end result is that you have quite a degree of tuning control over the process. If memory is a limitation and throughput can be sacrificed, try lowering the soft and hard limit and increasing the soft wait.</p><p>If performance is absolute and you have lots of memory, then increase the soft and hard limit and reduce the soft wait. This encourages Tapestry to create more page instances and not wait as long to re-use existing instances.</p></div>
</div>
<div class="clearer"></div>
Modified: websites/production/tapestry/content/request-processing.html
==============================================================================
--- websites/production/tapestry/content/request-processing.html (original)
+++ websites/production/tapestry/content/request-processing.html Wed Nov 11 12:19:45 2015
@@ -125,7 +125,7 @@
</div>
</li></ul>
-</div><p><strong>Request Processing</strong> involves a sequence of steps that Tapestry performs when every HTTP request comes in. You <em>don't need</em> to know these steps to use Tapestry productively, but understanding the request processing pipeline is helpful if you want to understand Tapestry deeply.</p><p>Much of the early stages of processing are in the form of extensible <a href="pipelinebuilder-service.html">pipelines</a>.</p><h2 id="RequestProcessing-TapestryFilter">Tapestry Filter</h2><p>All incoming requests originate with the TapestryFilter, which is a servlet filter configured inside your application's <a href="configuration.html">web.xml</a>.</p><p>The TapestryFilter is responsible for a number of startup and initialization functions.</p><p>When it receives a request, the TapestryFilter obtains the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/HttpServletRequestHandler.html">HttpServletRequestHandler</a> s
ervice, and invokes its service() method.</p><h2 id="RequestProcessing-HttpServletRequestHandlerPipeline">HttpServletRequestHandler Pipeline</h2><p>This pipeline performs initial processing of the request. It can be extended by contributing a <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/HttpServletRequestFilter.html">HttpServletRequestFilter</a> into the HttpServletRequestHandler service's configuration.</p><p>Tapestry does not contribute any filters into this pipeline of its own.</p><p>The terminator for the pipeline does two things:</p><ul><li>It stores the request and response into the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestGlobals.html">RequestGlobals</a> service. This is a per-thread scoped service that stores per-thread/per-request information.</li><li>It wraps the request and response as a <a class="external-link" href="http://tapestry.apache.o
rg/current/apidocs/org/apache/tapestry5/services/Request.html">Request</a> and <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/Response.html">Response</a>, and passes them into the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestHandler.html">RequestHandler</a> pipeline.</li></ul><h2 id="RequestProcessing-RequestHandlerPipeline">RequestHandler Pipeline</h2><p>This pipeline is where most extensions related to requests take place. Request represents an abstraction on top of HttpServletRequest. (Primarily, this exists to bridge from the Servlet API objects to the corresponding Tapestry objects. This is the basis for the planned portlet integration for Tapestry.) Where other code and services within Tapestry require access to information in the request, such as query parameters, that information is obtained from the Request (or Response) objects.</p><p>The RequestHand
ler pipeline includes a number of built-in filters:</p><ul><li>CheckForUpdates is responsible for <a href="class-reloading.html">class and template reloading</a>.</li><li>Localization identifies the <a href="localization.html">locale for the user</a>.</li><li>StaticFiles checks for URLs that are for static files (files that exist inside the web context) and aborts the request, so that the servlet container can handle the request normally.</li><li>ErrorFilter catches uncaught exceptions from the lower levels of Tapestry and presents the exception report page. This involves the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestExceptionHandler.html">RequestExceptionHandler</a> service, which is responsible for initializing and rendering the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/corelib/pages/ExceptionReport.html">core/ExceptionReport</a> page.</li></ul><p>The termi
nator for this pipeline stores the Request and the Response into RequestGlobals, then requests that the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/Dispatcher.html">MasterDispatcher</a> service figure out how to handle the request (if it is, indeed, a Tapestry request).</p><h2 id="RequestProcessing-MasterDispatcherService">Master Dispatcher Service</h2><p>The MasterDispatcher service is a chain-of-command, aggregating together (in a specific order), several Dispatcher objects. Each Dispatcher is built to recognize and process a particular kind of URL.</p><h3 id="RequestProcessing-RootPathDispatcher">RootPath Dispatcher</h3><p>The RootPath Dispatcher recognizes a request for the application root (i.e., "/") and handles this the same as a render request for the "Start" page. Support for the Start page is kept for legacy purposes. Index pages are the correct approach.</p><h3 id="RequestProcessing-AssetDispatcher">Asset Dispat
cher</h3><p>Requests that begin with "/assets/" are references to <a href="assets.html">asset resources</a> that are stored on the classpath, inside the Tapestry JARs (or perhaps inside the JAR for a component library). The contents of the file will be delivered to the client browser as a byte stream. This dispatcher also handles requests that are simply polling for a change to the file.</p><h3 id="RequestProcessing-PageRenderDispatcher">PageRender Dispatcher</h3><p>Page render requests are requests to render a particular page. Such requests may include additional elements on the path, which will be treated as activation context (see ComponentEvent Dispatcher below). Generally speaking, the activation context is the primary key of some related entity object. This allows the page to reconstruct the state it will need to successfully render itself.</p><p>The event handler method for the activate event may return a value; this is treated the same as the return value from a component a
ction request; typically this will result in a redirect to another page. In this way, the activate event can perform simple validation at the page level ("can the user see this page?").</p><p>Page render URLs consist of the logical name of the page plus additional path elements for the activation context. The dispatcher here strips terms off of the path until it finds a known page name. Thus, "/mypage/27" would look first for a page whose name was "mypage/27", then look for a page name "mypage". Assuming the second search was successful, the page would be activated with the context "27". If no logical page name can be identified, control passes to the next dispatcher.</p><h3 id="RequestProcessing-ComponentEventDispatcher">ComponentEvent Dispatcher</h3><p>The ComponentEvent dispatcher is used to trigger events in components.</p><p>The URL identifies the name of the page, then a series of component ids (the path from the page down to the specific component), then the name of the event
to be triggered on the component. The remaining path elements are used as the context for the <em>event</em> (not for the page activation, which does not currently apply). For example, "/griddemo.FOO.BAR/3" would locate page "griddemo", then component "FOO.BAR", and trigger an event named "action" (the default event type, which is omitted from the URL), with the context "3".</p><p>If the page in question has an activation context, it is supplied as an additional query parameter on the link.</p><p>In cases where the event type is not the default, "action", it will appear between the nested component id and the event context, preceded by a colon. Example: "/example/foo.bar:magic/99" would trigger an event of type "magic". This is not common in the vanilla Tapestry framework, but will likely be more common as Ajax features (which would not use the normal request logic) are implemented.</p><p>The response from a component action request is typically, but not universally, used to send a
redirect to the client; the redirect URL is a page render URL to display the response to the event. This is detailed under <a href="page-navigation.html">Page Navigation</a>.</p><h2 id="RequestProcessing-RequestGlobalsService">RequestGlobals Service</h2><p>The RequestGlobals service has a life cycle of per-thread; this means that a separate instance exists for every thread, and therefore, for every request. The terminators of the two handler pipelines store the request/response pairs into the RequestGlobals service.</p><h2 id="RequestProcessing-RequestService">Request Service</h2><p>The Request service is a <a href="shadowbuilder-service.html">shadow</a> of the RequestGlobals services' request property. That is, any methods invoked on this service are delegated to the request object stored inside the RequestGlobals.</p><h2 id="RequestProcessing-Overview">Overview</h2><p>The following diagram provides an overview of how the different pipelines, filters and dispatchers interact whe
n processing an incoming request.</p><p><span class="confluence-embedded-file-wrapper"><img class="confluence-embedded-image confluence-content-image-border" src="request-processing.data/tapestry_request_processing_800.png"></span></p></div>
+</div><p><strong>Request Processing</strong> involves a sequence of steps that Tapestry performs when every HTTP request comes in. You <em>don't need</em> to know these steps to use Tapestry productively, but understanding the request processing pipeline is helpful if you want to understand Tapestry deeply.</p><p>Much of the early stages of processing are in the form of extensible <a href="pipelinebuilder-service.html">pipelines</a>.</p><h2 id="RequestProcessing-TapestryFilter">Tapestry Filter</h2><p>All incoming requests originate with the TapestryFilter, which is a servlet filter configured inside your application's <a href="configuration.html">web.xml</a>.</p><p>The TapestryFilter is responsible for a number of startup and initialization functions.</p><p>When it receives a request, the TapestryFilter obtains the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/HttpServletRequestHandler.html">HttpServletRequestHandler</a> s
ervice, and invokes its service() method.</p><h2 id="RequestProcessing-HttpServletRequestHandlerPipeline">HttpServletRequestHandler Pipeline</h2><p>This pipeline performs initial processing of the request. It can be extended by contributing a <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/HttpServletRequestFilter.html">HttpServletRequestFilter</a> into the HttpServletRequestHandler service's configuration.</p><p>Tapestry does not contribute any filters into this pipeline of its own.</p><p>The terminator for the pipeline does two things:</p><ul><li>It stores the request and response into the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestGlobals.html">RequestGlobals</a> service. This is a per-thread scoped service that stores per-thread/per-request information.</li><li>It wraps the request and response as a <a class="external-link" href="http://tapestry.apache.o
rg/current/apidocs/org/apache/tapestry5/services/Request.html">Request</a> and <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/Response.html">Response</a>, and passes them into the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestHandler.html">RequestHandler</a> pipeline.</li></ul><h2 id="RequestProcessing-RequestHandlerPipeline">RequestHandler Pipeline</h2><p>This pipeline is where most extensions related to requests take place. Request represents an abstraction on top of HttpServletRequest. (Primarily, this exists to bridge from the Servlet API objects to the corresponding Tapestry objects. This is to allow for a possible portlet integration for Tapestry.) Where other code and services within Tapestry require access to information in the request, such as query parameters, that information is obtained from the Request (or Response) objects.</p><p>The RequestHandle
r pipeline includes a number of built-in filters:</p><ul><li>CheckForUpdates is responsible for <a href="class-reloading.html">class and template reloading</a>.</li><li>Localization identifies the <a href="localization.html">locale for the user</a>.</li><li>StaticFiles checks for URLs that are for static files (files that exist inside the web context) and aborts the request, so that the servlet container can handle the request normally.</li><li>ErrorFilter catches uncaught exceptions from the lower levels of Tapestry and presents the exception report page. This involves the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/RequestExceptionHandler.html">RequestExceptionHandler</a> service, which is responsible for initializing and rendering the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/corelib/pages/ExceptionReport.html">core/ExceptionReport</a> page.</li></ul><p>The termina
tor for this pipeline stores the Request and the Response into RequestGlobals, then requests that the <a class="external-link" href="http://tapestry.apache.org/current/apidocs/org/apache/tapestry5/services/Dispatcher.html">MasterDispatcher</a> service figure out how to handle the request (if it is, indeed, a Tapestry request).</p><h2 id="RequestProcessing-MasterDispatcherService">Master Dispatcher Service</h2><p>The MasterDispatcher service is a chain-of-command, aggregating together (in a specific order), several Dispatcher objects. Each Dispatcher is built to recognize and process a particular kind of URL.</p><h3 id="RequestProcessing-RootPathDispatcher">RootPath Dispatcher</h3><p>The RootPath Dispatcher recognizes a request for the application root (i.e., "/") and handles this the same as a render request for the "Start" page. Support for the Start page is kept for legacy purposes. Index pages are the correct approach.</p><h3 id="RequestProcessing-AssetDispatcher">Asset Dispatch
er</h3><p>Requests that begin with "/assets/" are references to <a href="assets.html">asset resources</a> that are stored on the classpath, inside the Tapestry JARs (or perhaps inside the JAR for a component library). The contents of the file will be delivered to the client browser as a byte stream. This dispatcher also handles requests that are simply polling for a change to the file.</p><h3 id="RequestProcessing-PageRenderDispatcher">PageRender Dispatcher</h3><p>Page render requests are requests to render a particular page. Such requests may include additional elements on the path, which will be treated as activation context (see ComponentEvent Dispatcher below). Generally speaking, the activation context is the primary key of some related entity object. This allows the page to reconstruct the state it will need to successfully render itself.</p><p>The event handler method for the activate event may return a value; this is treated the same as the return value from a component act
ion request; typically this will result in a redirect to another page. In this way, the activate event can perform simple validation at the page level ("can the user see this page?").</p><p>Page render URLs consist of the logical name of the page plus additional path elements for the activation context. The dispatcher here strips terms off of the path until it finds a known page name. Thus, "/mypage/27" would look first for a page whose name was "mypage/27", then look for a page name "mypage". Assuming the second search was successful, the page would be activated with the context "27". If no logical page name can be identified, control passes to the next dispatcher.</p><h3 id="RequestProcessing-ComponentEventDispatcher">ComponentEvent Dispatcher</h3><p>The ComponentEvent dispatcher is used to trigger events in components.</p><p>The URL identifies the name of the page, then a series of component ids (the path from the page down to the specific component), then the name of the event t
o be triggered on the component. The remaining path elements are used as the context for the <em>event</em> (not for the page activation, which does not currently apply). For example, "/griddemo.FOO.BAR/3" would locate page "griddemo", then component "FOO.BAR", and trigger an event named "action" (the default event type, which is omitted from the URL), with the context "3".</p><p>If the page in question has an activation context, it is supplied as an additional query parameter on the link.</p><p>In cases where the event type is not the default, "action", it will appear between the nested component id and the event context, preceded by a colon. Example: "/example/foo.bar:magic/99" would trigger an event of type "magic". This is not common in the vanilla Tapestry framework, but will likely be more common as Ajax features (which would not use the normal request logic) are implemented.</p><p>The response from a component action request is typically, but not universally, used to send a r
edirect to the client; the redirect URL is a page render URL to display the response to the event. This is detailed under <a href="page-navigation.html">Page Navigation</a>.</p><h2 id="RequestProcessing-RequestGlobalsService">RequestGlobals Service</h2><p>The RequestGlobals service has a life cycle of per-thread; this means that a separate instance exists for every thread, and therefore, for every request. The terminators of the two handler pipelines store the request/response pairs into the RequestGlobals service.</p><h2 id="RequestProcessing-RequestService">Request Service</h2><p>The Request service is a <a href="shadowbuilder-service.html">shadow</a> of the RequestGlobals services' request property. That is, any methods invoked on this service are delegated to the request object stored inside the RequestGlobals.</p><h2 id="RequestProcessing-Overview">Overview</h2><p>The following diagram provides an overview of how the different pipelines, filters and dispatchers interact when
processing an incoming request.</p><p><span class="confluence-embedded-file-wrapper"><img class="confluence-embedded-image confluence-content-image-border" src="request-processing.data/tapestry_request_processing_800.png"></span></p></div>
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