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Re: [jetty-users] Jetty + Slf4j 
Hi Hugues,

The default setup for a webapp context is that a webapp will be
prevented from loading the slf4j classes from the server's
classpath, *but a webapp can provide their own copy of these jars
in WEB-INF/lib*. 
I've just tested this to confirm it works with 6.1.22 (and jdk1.5 and jdk1.4).
If I use the slf4j apis in a webapp, and don't provide the slf4j-api and an
slf4j impl jar in my webapp, I get ClassNotFound exceptions. However,
if I do provide these jars, then my webapp works happily and the jetty
logging is unaffected.

Note that I specifically mention the version of the jdk. This is simply
because with jdk < 1.5, the server path will have no slf4j jars on it
anyway, because they are only present in $JETTY-HOME/lib/jsp-2.0, which
start.jar only puts on the classpath iff jdk < 1.5.

So in short, you're absolutely right that the default setup guarantees
isolation of logging between a webapp and the server. An app should be able to put their own copies of slf4j into their WEB-INF/lib and it should just work. However, if they want to, they can take the org.slf4j. 
package out of the list of serverClasses for a webapp and they should
be able to see and use the jars from the server's classpath.
BTW looking at your jetty6-web.xml file, I don't see anything related to the slf4j package? 

cheers
Jan

Hugues Malphettes wrote:

Hi Julio,
We faced this issue with jetty6 with the standard distribution.
We chose to do this:
1- remove *slf4j*, commons-logging, log4j jars from the webapp.
2- add a jetty6-web.xml inside the WEB-INF of our web-application that
contains this xml:
<?xml version="1.0"  encoding="ISO-8859-1"?>
<Configure class="org.mortbay.jetty.webapp.WebAppContext">
    <Set name="serverClasses">
        <Array type="java.lang.String">
            <Item>-org.mortbay.jetty.plus.jaas.</Item>
            <Item>org.mortbay.jetty.</Item>
        </Array>
    </Set>
</Configure>

Jetty6 does something special with the webapp classloader that
prevents a web-application to access the org.slf4j.* classes that are
provided by the server's classloader. I have not really understood the
reason for this; although I am guessing it is to support some
isolation of the logging for each webapp.
Adding this jetty6-web.xml will basically let your webapp access the
shared slf4j. slf4j will locate the other *slf4j* jars in the server's
classes loader.


This setup will enforce "centralized" logging in jetty6:
the configuration of the logging is done in one single place:
${jetty.home}/resources/log4j.properties (or logback.xml)
for all web-applications.
You should add log4j.jar inside the shared libraries (or
logback-core+logback-classic). In the standard distribution of jetty6
that would be inside ${jetty.home}/lib/ext.
I am not sure where it is in the debian distribution.


Jetty7 will support configuration of centralized logging as an option
and I believe will not have this kind of difficult issue anymore.

I hope this helps,
Hugues.

On Tue, Dec 8, 2009 at 10:39 AM, Julio Viegas
<julioviegas@xxxxxxxxxxxxxxx> wrote:

Hello Diego,

  How are you starting Jetty? I mean, can you check your Jetty's JVM
classpath setting?

  I suspect "jar:file:/usr/share/java/slf4j-simple-1.5.8.jar" is
inside your $CLASSPATH or something like that...

Rgrds,
JV -- julioviegas.com

On Tue, Dec 8, 2009 at 16:26, Diego Plentz <diego@xxxxxxxxxx> wrote:

Hey guys,
I'm using jetty 6.1.x installed through apt-get in a Ubuntu box. When I
deploy my application, I have a problem with slf4j. If I deploy my war with
slf4j-log4j12-1.5.8.jar, I have this message:
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in
[jar:file:/usr/share/java/slf4j-simple-1.5.8.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in
[jar:file:/var/cache/jetty/Jetty_0_0_0_0_8080_suporte_promotor.war___suporte.promotoronline.com.br_ivstzq/webapp/WEB-INF/lib/slf4j-log4j12-1.5.8.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an
explanation.
But, if I remove the jar from the war file, I have a NoClassDefFoundError:
Caused by: java.lang.NoClassDefFoundError: org/slf4j/impl/StaticLoggerBinder
at org.slf4j.LoggerFactory.getSingleton(LoggerFactory.java:223)
at org.slf4j.LoggerFactory.bind(LoggerFactory.java:120)
at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:111)
at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:269)
....
What is the correct behavior?
--
http://plentz.org
http://twitter.com/plentz

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--
Jan Bartel, Webtide LLC | janb@xxxxxxxxxxx | http://www.webtide.com

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