Logging with embedded Jetty and Tapestry

Question 1

Alright, thanks for help joostschouten and user2424794. I've got it working.

The mvn dependency:tree revealed, that other web app's dependency: qpid-client imported another slf4j-api to the war.
So another exclusion was necessary:

<dependency>
    <groupId>org.apache.qpid</groupId>
    <artifactId>qpid-client</artifactId>
    <version>0.22</version>
    <exclusions>
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
        </exclusion>
    </exclusions>
</dependency>

For the record, the tapestry-core dependency:

<dependency>
    <groupId>org.apache.tapestry</groupId>
    <artifactId>tapestry-core</artifactId>
    <version>${tapestry-release-version}</version>
    <exclusions>  
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
        </exclusion>
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
        </exclusion>
        <exclusion>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
        </exclusion>
    </exclusions>
</dependency>

The only problem left is that the war wouldn't compile without the slf4j-api, therefore I add it as war dependency for the compilation, not for the linking - maven's provided scope:

<dependency>
     <groupId>org.slf4j</groupId>
     <artifactId>slf4j-api</artifactId>
     <version>1.7.5</version>
     <scope>provided</scope>
</dependency>

Of course, the slf4j-api , slf4j-log4j12 and log4j are added as dependencies for the server, which 'provides' it to the war application.

Now everything compiles, runs and logs just fine.

Question 2

You have a dependency problem. Instead of using exclusion all the time I see the dependency tree and reorder the tags inside pom.xml. The rule here seams that the first appearance of the dependency wins. So when you want that a inherited dependency is omitted by another one, just move the dependency tag before the one you want the inherited dependency omitted.

That makes the pom more readable and also controls which version of the dependencies in the trees are used. In only rare cases I have to use the tag.

Question 3

The problem is that you have two versions of slf4j-log4j12 on your classpath. By the looks of it you are managing to exclude the later version in stead of the older one. Slf4j is complaining about the fact it is expecting a newer version than the one it is finding.

It seems to me that the 1.6.1 version makes it onto your classpath though your embedded jetty server. Have you setup your jetty dependency through maven as well? If so, add the exclude to your jetty dependency too. Either way, you need to inspect your classpath and resolve the conflicting versions one way or the other