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$Id: RELEASE-NOTES.txt 399403 2006-05-03 20:16:16Z rdonkin $
Commons Logging Package
Version 1.1.0
Release Notes
INTRODUCTION:
============
This release of Jakarta Commons Logging (JCL) is a maintenance release, with a
few new configuration features but no major changes in services provided.
This release introduces significant changes in the way that discovery of
logging implementations occurs, and how errors are handled. A number of
problems that have troubled users in past releases (particularly the
"Log4JLogger does not implement Log" problem) will hopefully be
significantly reduced or cured.
This release is 100% compatible with existing code that calls
commons-logging. There are some incompatibilities with code that extends
commons-logging, for example to implement custom logging adapters. See
the compatibility section for details.
All core classes were compiled with a 1.2.x JDK. JCL may work on some
augmented 1.1 series JREs but it is recommended that those wish to run
on 1.1 JREs download the source and create a custom implementation by
stripping out all the complex classloader management code.
For further details, please see the Jakarta Commons Logging website:
http://jakarta.apache.org/commons/logging.
For the very latest news, hints, FAQs etc. please see the
Jakarta Commons Logging wiki site:
http://wiki.apache.org/jakarta-commons/Logging
Note that some containers (some versions of Apache Tomcat and JBoss in
particular) prevent webapps, ejbs, etc from overriding the commons-logging
implementation provided by the container. This means that bundling this
updated implementation with a deployed application may not have any effect.
See the commons-logging site and/or the wiki for more information.
== New Features ==
* Jar files now have release-numbers embedded in the names, for easier management.
* New jar file commons-logging-adapters-xxx.jar is now provided. This can be
used to resolve class cast conflicts where parts of commons-logging are
deployed via different classloaders. It is not expected to be frequently
used; it is only necessary in situations where a container has deployed
commons-logging-api.jar and a webapp wants to bind to a third-party
logging implementation such as log4j. In this case, the webapp can
experience problems if it deploys commons-logging.jar as this causes
duplicates of the core commons-logging classes, but commons-logging-adapters
can be safely used.
* New internal diagnostics feature. If commons-logging is behaving in an
unexpected manner, you can now set system property
org.apache.commons.logging.diagnostics.dest
to the value STDOUT, STDERR or a filename. As commons-logging initialises
itself for each new contextClassLoader it detects, useful information will
be output about which logging library is bound to and why.
* JCL now prefers to "make a best attempt" in problem scenarios rather than
report an error and fail to initialise. New configurable attributes
ALLOW_FLAWED_HIERARCHY, ALLOW_FLAWED_DISCOVERY and ALLOW_FLAWED_CONTEXT are
provided to control startup behavior. The default values for these are all
true, meaning that commons-logging attempts to recover from bad logging
configuration situations by finding *some* logger to use even when it isn't
quite the one that might be expected. This will significantly reduce the
occurrence of the dreaded LogConfigurationException on application/webapp
startup at the cost of slightly more ambiguity about where output will go.
In cases where no logging output is generated or wanted (which is the case
99% of the time) this is definitely a more convenient approach. Users who
cannot figure out where logging went or why it went to an unexpected
destination can enable diagnostics to find out, or set the ALLOW_FLAWED_
settings to false to force LogConfigurationException to be thrown as in
earlier releases.
* Fix for the problem where memory was not being released under some circumstances
when a webapp was undeployed. An internal change fixes some situations where
that occurs (by using weak references); this requires no action on the part of
users of this library. In addition, a utility class ServletContextCleaner is
provided in the jar file which is expected to resolve this problem in all
situations; however it is necessary for an application to define this class as
a ServletContextListener in the web.xml in order for this to be invoked.
* Prioritised commons-logging.properties files. A file with the name
"commons-logging.properties" placed in the classpath can be used to set
various JCL configuration options. In previous releases, the first
such file found in the classpath was used to configure JCL. Now, each file
can have an entry "priority", and the file with the highest priority is used.
Where two files have equal priority, the first one in the classpath is used;
this maintains backwards compatibility.
* New feature to disable loading of logging classes via the thread context
classloader (TCCL), on a per-webapp basis. Simply putting an entry
"use_tccl=false" in a commons-logging.properties file will ensure that
all classes used for logging are loaded via the same classloader that
loads the LogFactory class. This resolves any "class cast" issues with
JCL, though at the price of losing some control over logging configuration.
* The log4j logging adapter now supports the TRACE level (added to log4j 1.2.12).
Formerly, any calls to log.trace were output at the log4j debug level.
* Better behaviour for systems with null classloaders (generally embedded systems).
* New zip file containing source and javadocs for those using modern IDEs.
== Incompatibilities ==
There are no changes for code that calls LogFactory or Log methods. This means
that any application which is a simple "user" of the JCL library can safely
upgrade to this version.
All changes to JCL configuration are backwards compatible.
Classes Log4JCategoryLog and Log4jFactory have been removed; these were both
deprecated in the 1.0.3 release (April 2003).
For code that extends the JCL LogFactoryImpl class, the isXXXAvailable methods
in org.apache.commons.logging.impl.LogFactoryImpl are no longer called during
discovery by that class. Therefore classes which subclass LogFactoryImpl and
override those methods will not have their methods called. This is a pretty
unusual thing to do, so it isn't expected that any apps will actually be
affected by this.
AvalonLog is no longer serializable. The semantics were always deeply
unsatisfactory. It is cleaner and clearer to admit the truth.
== Deprecation Note ==
Previous releases of commons-logging-api.jar contained the Jdk14Logger class;
this is now deprecated. It will be removed from the API jar in some future
release.
== Dependencies ==
Commons-logging has no mandatory dependencies.
Java 1.2 and later are supported. It may be possible to use this release with
java 1.1 but this has not been tested; the unit tests certainly don't run on
that version.
== Distributed Jar Files ==
File commons-logging-nn.jar is the one most people will want. It provides the
base implementation and adapters to a number of popular logging libraries.
File commons-logging-adapters-nn.jar includes only the adapters to various
concrete logging libraries. When commons-logging-nn.jar or
commons-logging-api-nn.jar is deployed in a container classpath, then this
adapters-only jar file should be deployed in the webapp, not the complete JCL
distribution. This ensures that the core Log/LogFactory classes are only
deployed via one classloader, thus avoiding "Log4JLogger does not implement Log"
and similar problems.
File commons-logging-api-nn.jar provides minimal adapters to external logging
libraries, just the internally implemented SimpleLog and NoOpLog classes
plus Jdk14Logger (which is currently required by Apache Tomcat).
This jar file may be used as a declared dependency for projects that care about
"transitive dependencies" and can't handle jar files such as commons-logging-nn.jar
which have "optional" dependencies depending on how they are used. In addition,
this jar file can be useful for "rebundlers" of JCL who recompile the source-code
but who may not be able to recompile against the full set of supported adapters;
such projects should be able to at least recreate an equivalent of this jar file.
== General Notes ==
The jakarta commons project has migrated to the Subversion version control system
(previously, CVS was used). There should be no effect on users of the JCL
library, but obviously the process of examining the latest source code, and of
creating patches for JCL has now changed. Please see the jakarta commons
website for details (http://jakarta.apache.org/commons).
== Bugs Fixed ==
* 31597: problem where log4j adapter was in parent classloader but log4j.jar was
in child classloader led to failure to initialise logging has been
fixed.
* 31710, 10825: commons-logging now works better in systems where getClassLoader
returns null. This essentially means embedded systems.
* 31818: workaround for bug in java1.2 compiler; code now compiles under 1.2
* Log4JCategoryLog has been removed from the main distribution jar; it has been
deprecated for a long while. Replacement class Log4JLogger should be a completely
transparent replacement for all commons-logging users.
* package.html files are no longer present in the jar files, removing nuisance
javadoc warnings when building javadoc for apps using jcl.
* In several cases, LogConfigurationException objects were being wrapped in
other LogConfigurationException objects. These have (hopefully) all been
fixed.
DEPRECATIONS:
============
(These are carried forward from Version 1.0.4)
[LogSource] Previously deprecated, replaced by LogFactory.
