Nick Williams created LOG4J2-270:
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Summary: Improve logging initialization in Servlet containers;
reduce amount of extra configuration needed in these contexts
Key: LOG4J2-270
URL: https://issues.apache.org/jira/browse/LOG4J2-270
Project: Log4j 2
Issue Type: Improvement
Components: Core
Affects Versions: 2.0-beta6, 2.0-beta7
Reporter: Nick Williams
Assignee: Nick Williams
[Note: This has been pulled from discussions surrounding LOG4J2-223.
Specifically, the description below comes from [this
comment|https://issues.apache.org/jira/browse/LOG4J2-223?focusedCommentId=13668682&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13668682].]
Okay, based on all of this, here are my suggestions on how I would improve this
(sorry for my scarcity lately ... trying to catch up on chapters for the book).
These suggestions are based on the following goals:
# Design web application support so that users of simple Log4j configurations
(not using JNDI lookups for logging configuration) don't have to do any
additional configuration to get Log4j to "just work" in a Servlet container.
This goal is made with the understanding that this is only possible for users
of Servlet 3.0, 3.1, or higher. Users of Servlet 2.5 will have to manually
configure listeners and filters. It's the only way.
# Eliminate the need for web applications to have an additional JAR just to
support proper configuration.
# Improve the documentation considerably so that it is abundantly clear how
Log4j works in web applications.
With these goals in mind, here are my recommendations:
* Get rid of the log4j-web module and move this stuff into log4j-core. We'll
need [~timothyjward]'s input on how this could impact OSGi support. In theory,
I don't think we should have a problem. No other Log4j classes will refer to
the listener or filter. These classes will only ever get loaded BY the Servlet
container, in which case the Servlet API will already be loaded, so I don't
think it would be possible to get {{NoClassDefFoundError}} s.
* Create a {{/META-INF/web-fragment.xml}} file with the contents noted below.
This will ensure that the Log4j fragment is loaded before any other fragments.
* Create a {{Log4jWebInitializer}} class (doesn't implement any interfaces,
package-private) to properly initialize and de-initialize Log4j in a Servlet
container. It works like this: If the context parameters currently required by
the {{JNDIContextFilter}} exist, it initializes Log4j the way
{{JNDIContextFilter}} currently does. If they don't exist, it initializes Log4j
the way {{Log4jContextListener}} currently does.
* Create a {{Log4jServletContainerInitializer implements
ServletContainerInitializer}} and a
{{/META-INF/services/javax.servlet.ServletContainerInitializer}} file to go
along with it. This initializer:
** Initializes Log4j properly using the {{Log4jWebInitializer}}.
** Installs a private listener to de-initialize Log4j when the container shuts
down the application using the {{Log4jWebInitializer}}.
** Installs the {{NamedContextFilter}} (renamed from {{JNDIContextFilter}}),
which doesn't do any initialization/deinitialization, it just does what it
currently does for {{doFilter}}.
* Change the existing {{Log4jContextListener}} to use the
{{Log4jWebInitializer}}.
* Create a new manual page directly under the "MANUAL" menu heading on the
homepage that explains how to use Log4j in a Servlet container:
** If you're using Servlet 3.0 or higher, it "just works," but if you're also
using JNDI you need to create the proper context parameters.
** If you're using Servlet 2.5, you MUST add the {{Log4jContextListener}} (and
the {{NamedContextFilter}} and context parameters if you're using JNDI) to your
deployment descriptor.
Now, to address some questions:
# "What to do about JBoss 5, which doesn't support web-fragment.xml?" JBoss 5
doesn't support web-fragment.xml because it's a Servlet 2.5 container, not a
Servlet 3.0 container. Users of JBoss 5 would follow the Servlet 2.5
instructions just like all other users. Users of JBoss 6, 7, 8, etc., would
follow the Servlet 3.0 instructions ("don't do anything").
# "A container with multiple web applications. The Log4j jars are in the Tomcat
classpath and they all share the same configuration file." versus "A container
with multiple web applications. Each has their own copy of the log4j jars and
each has their own configuration file." Easy! The
{{Log4jServletContainerInitializer}} will get executed for every application,
whether the Log4j JARs are in the Tomcat classpath or in /WEB-INF/lib (this is
per the Servlet specification). Each application will get its own context.
Regardless of where the JARs are, that context will load the application's
configuration file if it has its own, and will load the shared configuration if
it doesn't have its own.
Thoughts?
{code:xml|title=web-fragment.xml}<web-fragment ... metadata-complete="true">
<name>log4j</name>
<distributable/>
<ordering>
<before>
<others/>
</before>
</ordering>
</web-fragment>{code}
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