tapestry-core/src/site/apt/guide/logging.apt

 ----
  Logging
 ----
 
Logging of Tapestry Components and Pages

  Tapestry makes extensive use of
  {{{http://www.slf4j.org/}SLF4J}} to log details about the creation and operation of your page and component classes.
  
  The default configuration for logging uses 
  {{{http://logging.apache.org/log4j/}Log4J}} as the logging toolkit, though
  {{{../../tapestry-ioc/logging.html}this can be changed}}.
  
  
Class to Logger

  The logger name for a page or component matches the fully qualified class name.  You can configure this in log4j.properties:
  
----
log4j.category.org.apache.tapestry5.integration.app1.pages.MerryChristmas=trace
----
  
Injecting Loggers

  You may mark a field of type 
  {{{http://www.slf4j.org/api/org/slf4j/Logger.html}Logger}} with the @Inject annotation.  The proper Logger for your
  page or component will be injected.
  
---
public class MyPage
{
  @Inject
  private Logger logger;
  
  . . .
---

@Log annotation

  You may mark any component method with the {{{../../apidocs/org/apache/tapestry5/annotations/Log.html}Log}} annotation.
  Method entry, exit (and any thrown exceptions) will be logged at DEBUG level. This is very convienient for
  debugging, especially when placed on event handler methods.


DEBUG Level

  When a component's logger is configured at the DEBUG level, you will also see added output when the class is first
  accessed identifying how Tapestry is modifying the bytecode of the class.  
  
  Example:
  
---
[DEBUG] MerryChristmas Finished class transformation: InternalClassTransformation[
public org.apache.tapestry5.integration.app1.pages.MerryChristmas extends java.lang.Object
  implements org.apache.tapestry5.runtime.Component, org.apache.tapestry5.runtime.RenderCommand

add default method: public void postRenderCleanup()
<default>

add default method: public void setupRender(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void beginRender(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void beforeRenderTemplate(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void afterRenderTemplate(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void beforeRenderBody(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void afterRenderBody(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void afterRender(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public void cleanupRender(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.Event $2)
<default>

add default method: public boolean handleComponentEvent(org.apache.tapestry5.runtime.ComponentEvent $1)
<default>

add default method: public org.apache.tapestry5.ComponentResources getComponentResources()
<default>

add default method: public void containingPageDidLoad()
<default>

add default method: public void containingPageDidDetach()
<default>

add default method: public void containingPageDidAttach()
<default>

add field: protected final org.apache.tapestry5.internal.InternalComponentResources _$resources;

replace method: public final org.apache.tapestry5.ComponentResources getComponentResources()
return _$resources;

add default method: public void render(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.RenderQueue $2)
<default>

replace method: public void render(org.apache.tapestry5.MarkupWriter $1, org.apache.tapestry5.runtime.RenderQueue $2)
_$resources.queueRender($2);

convert default constructor: initializer();

add constructor: org.apache.tapestry5.integration.app1.pages.MerryChristmas(org.apache.tapestry5.internal.InternalComponentResources $1)
{
  _$resources = $1;
  initializer();

}

]
----

  Is this helpful?  Probably only if you are developing your own code that integrates into the component class transformation chain; for example,
  to support your own field and method annotations.
  
TRACE Level

  Enabling the TRACE level <for pages> results in extremely verbose logging of every activity that drives the rendering of output, such as each component
  working its way through the {{{rendering.html}rendering stage machine}}.  Example:
  
----
[TRACE] MerryChristmas Executing: ComponentPageElement[MerryChristmas]
[TRACE] MerryChristmas Executing: SetupRender[MerryChristmas]
[TRACE] MerryChristmas Executing: BeginRender[MerryChristmas]
[TRACE] MerryChristmas Executing: BeforeRenderTemplate[MerryChristmas]
[TRACE] MerryChristmas Executing: ComponentPageElement[MerryChristmas:border]
[TRACE] MerryChristmas Executing: SetupRender[MerryChristmas:border]
[TRACE] MerryChristmas Executing: BeginRender[MerryChristmas:border]
[TRACE] MerryChristmas Executing: BeforeRenderTemplate[MerryChristmas:border]
[TRACE] MerryChristmas Executing: Start[html]
[TRACE] MerryChristmas Executing: Text[
    ]
[TRACE] MerryChristmas Executing: Start[head]
[TRACE] MerryChristmas Executing: Text[
        ]
[TRACE] MerryChristmas Executing: Start[title]
[TRACE] MerryChristmas Executing: Text[Tapestry Integration Test Application #1]

  . . .
----

  Is this helpful?  Only if you are writing your own components and get an exception about unbalanced elements. This output gives
  you a detailed view into what has rendered and when, so you can track it down.