[logback-user] Configuring properties via XML

Adam Gordon adam.n.gordon at gmail.com
Fri Nov 9 01:42:03 CET 2012

I was able to get this working using the SiftingAppender.  Thanks!  My
request filter pulls the child app name from the URI and sets the MDC
variable which yields the appropriate behavior of Spring logging to the
correct log files.

One final question:  is this going to be subject to race conditions?  If
user A is using child app A at the same time as user B is using child app
B, they're going to go through the same request filter so it's feasible
that A's value gets set and that thread goes to do some intensive business
logic (which let's say has a bunch of logging), B's thread comes in and
changes the value, will A's thread suddenly switch log files?

I guess the real question is when does the SiftingAppender query MDC for
the value and when does it update it for the nested <appender>?



On Thu, Nov 8, 2012 at 2:27 PM, ceki <ceki at qos.ch> wrote:

> Have you looked at SiftingAppender [1]? If you can set an MDC variable at
> the beginning of a request served by each child app, the results should be
> rather close to what you are aiming. Give it a try.
> [1] http://logback.qos.ch/manual/**appenders.html#SiftingAppender<http://logback.qos.ch/manual/appenders.html#SiftingAppender>
> On 08.11.2012 19:54, Adam Gordon wrote:
>> Ok, I really should have thought about what I really needed before
>> posting.
>> We have a "parent" GWT web application and we have children applications
>> that are plugged into it.  The children can run as standalone web
>> applications but this is really only for development.  Since each child
>> can run independently, each has its own logback.xml file.
>> Unfortunately, when the parent is built, the children are just JAR file
>> dependencies and the parent also has it's own logback.xml file.
>> Using only the parent's logback.xml file, we can configure different
>> appenders (and thus different log files) for each of the children, but
>> this only works because of the child namespacing (the Java package
>> name).  The parent's logback.xml defines the root logger to use the
>> parent's appender.  What this means is that if the children are using a
>> common framework, say Spring, all the Spring logging doesn't go into the
>> correct child's logfile, but rather the parent's.
>> What we need is a way to either allow each child it's own, completely
>> separate logging configuration or we need to "tag" the logging statement
>> in the parent's log file with some name that indicates which child the
>> message came from.
>> I was looking at the concept of a context selector, but it wasn't clear
>> how I'd be able to configure this to return the correct LoggingContext
>> depending on which child issued the logging statement.
>> Alternatively, I suppose I could add a filter which "sets" the current
>> logging context based on the request URI - the children's request URIs
>> are also namespaced so that each child's request URI always starts with
>> /child_name/...
>> Was this clear?  Do anyone have any thoughts on how best to approach
>> this problem?
>> Thanks,
>> --adam
>> http://gordonizer.com
>> On Thu, Nov 8, 2012 at 11:01 AM, ceki <ceki at qos.ch <mailto:ceki at qos.ch>>
>> wrote:
>>     Please see [1] in the docs. For your use case, you need to define
>>     the property in the context scope [2].
>>     [1]
>>     http://logback.qos.ch/manual/_**_configuration.html#__**
>> variableSubstitution<http://logback.qos.ch/manual/__configuration.html#__variableSubstitution>
>>     <http://logback.qos.ch/manual/**configuration.html#**
>> variableSubstitution<http://logback.qos.ch/manual/configuration.html#variableSubstitution>
>> >
>>     [2] http://logback.qos.ch/manual/_**_configuration.html#scopes<http://logback.qos.ch/manual/__configuration.html#scopes>
>>     <http://logback.qos.ch/manual/**configuration.html#scopes<http://logback.qos.ch/manual/configuration.html#scopes>
>> >
>>     On 08.11.2012 18:54, Adam Gordon wrote:
>>         The Layout chapter indicates it supports property value
>>         retrieval via
>>         %property{key} and states that the logging context is where one
>>         might
>>         put a property (along w/ System properties).  I believe log4j
>>         did this
>>         w/ the <param name="key_name" value="some_value"> element in the
>>         <appender> and referenced it via %properties{key_name}.
>>         I'm not seeing how to do this in Logback in XML. Would it go in
>> the
>>         <logger> element?  What's the syntax?  Could someone please
>>         point me to
>>         the relevant section in the appropriate chapter of the manual?
>>         Thanks,
>>         --adam
> --
> Ceki
> 65% of statistics are made up on the spot
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