[slf4j-user] slf4j logger -> Servlet container log : How to?

[Jacob Kjome]

See comments inline below....

On 5/11/2010 10:42 AM, Thorbjoern Ravn Andersen wrote:
> Den 11/05/10 18.32, Jacob Kjome skrev:
>> In web.xml...
>>
>> <listener>
>> <listener-class>
>> org.apache.log4j.servlet.ServletContextLogAppenderListener
>> </listener-class>
>> </listener>
>>
>> in log4j.xml...
>>
>> <appender name="ServletContext"
>> class="org.apache.log4j.servlet.ServletContextLogAppender">
>> <param name="servletContextPath" value="/mycontext"/>
>> <param name="Threshold" value="debug"/>
>> <layout class="org.apache.log4j.PatternLayout">
>> <param name="ConversionPattern" value="[%-5p][%-8.8t]: %39.39c %x- %m"/>
>> </layout>
>> </appender>
>>
>> Notice the conversion pattern ends with "%m" instead of "%m%n". This
>> is because when the message goes through the servlet context logging
>> mechanism, the latter adds the newline, so adding it to the conversion
>> pattern above would result in 2 newlines, which is why we leave it out.

> Ok. So if I understand this correctly, your approach uses a servlet
> listener to register all contexts keyed by the last part of their
> context path, and you tell the appender in question which ServletContext
> to retrieve and then forward to that logger.
>

Each webapp that defines the servlet context listener can participate in servlet 
context logging.  However, how many contexts the the servlet context appender 
handles depends on how you set up classloading.  If you deploy the 
log4j-sandbox.jar, along with log4j.jar, in WEB-INF/lib and use child-first 
classloading, then the servlet context appender will only ever deal with a single 
context; the current one.  On the other hand, if log4j-sandbox.jar and log4j.jar 
are shared, e.g., at the container level, then it would handle more context paths.

> Will this also work with multiple web apps using slf4j, or will they go
> to the same appender?
>

It's been a while since I used it or studied it closely, but it should handle as 
many contexts as you give it.  Note that I've never tried it via SLF4J, only 
directly using Log4j.

BTW, the way I've used this in the past is either to place the jars in WEB-INF/lib 
and use child-first classloading or use a logger repository selector.  I always 
manually configure Log4j after letting the servlet context listener register the 
context to the appender.  Then in Tomcat, for instance, I place log4j.jar in a 
shared lib location along with log4j.properties, meant for configuring the server 
to use Log4j, which looks somewhat like below.  So, the server has its own log4j 
configuration while each webapp has its own configuration.  And when my app either 
logs directly to the servlet context or logs via the servlet context log appender, 
I have defined exactly where the output goes; to 
"${catalina.base}/logs/localhost_mycontext.log".

Oh, and I had to follow these instructions to get Tomcat to use Log4j...
http://tomcat.apache.org/tomcat-6.0-doc/logging.html#log4j

Jake


log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout
log4j.appender.A1.layout.ConversionPattern=%-5p[%-8.8t]: %39.39c %-6r - %m%n


log4j.appender.LOCALHOST=org.apache.log4j.RollingFileAppender
log4j.appender.LOCALHOST.File=${catalina.base}/logs/localhost.log
log4j.appender.LOCALHOST.MaxFileSize=1000KB
log4j.appender.LOCALHOST.MaxBackupIndex=1
log4j.appender.LOCALHOST.layout=org.apache.log4j.PatternLayout
log4j.appender.LOCALHOST.layout.ConversionPattern=%-5p[%-8.8t]: %39.39c %-6r - %m%n

log4j.appender.MYCONTEXT=org.apache.log4j.DailyRollingFileAppender
log4j.appender.MYCONTEXT.File=${catalina.base}/logs/localhost_mycontext.log
log4j.appender.MYCONTEXT.DatePattern='.'yyyy-MM-dd
log4j.appender.MYCONTEXT.layout=org.apache.log4j.PatternLayout
log4j.appender.MYCONTEXT.layout.ConversionPattern=%c{1} %-6r - %m%n

log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/mycontext]=DEBUG, 
MYCONTEXT
log4j.additivity.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/mycontext]=false

log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=INFO, 
LOCALHOST
log4j.additivity.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=false

log4j.logger.org.apache.coyote=INFO
log4j.logger.org.apache.catalina=INFO

log4j.rootLogger=WARN, A1