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>?

--adam

http://gordonizer.com



On Thu, Nov 8, 2012 at 2:27 PM, ceki <ceki@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


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@qos.ch <mailto:ceki@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>
    [2] 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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