Question

I’m developing with Grails 2.1.1 and now I want to integrate Logback (http://logback.qos.ch) as the default logging framework as it should provide some better logging features and could be also configured via Groovy.

As Logback 1.0.7 (latest) does only work with slf4j 1.6.6 I want to upgrade the Grails dependeny. Grails 2.1.1 is using slf4j 1.6.2. How to do this properly?

I tried the following: in BuildConfig.groovy I exclude grails-plugin-log4j and slf4j-api

grails.project.dependency.resolution = {
  // inherit Grails' default dependencies
  inherits("global") {
      excludes "grails-plugin-log4j", "slf4j-api"
  }
  ...
}

and I try to load slf4j-api 1.6.6 in compile build and runtime along with the other necessary libraries

grails.project.dependency.resolution = {
  ...
  dependencies {
    // specify dependencies here under either 'build', 'compile', 'runtime', 'test' or 'provided' scopes eg.

    compile "org.slf4j:slf4j-api:1.6.6"

    build   "org.slf4j:slf4j-api:1.6.6",
            "ch.qos.logback:logback-core:1.0.7",
            "ch.qos.logback:logback-classic:1.0.7"

    runtime "org.slf4j:slf4j-api:1.6.6",
            "org.slf4j:log4j-over-slf4j:1.6.6", // logback dependency for classic module, as seen on http://logback.qos.ch/dependencies.html
            "ch.qos.logback:logback-core:1.0.7",
            "ch.qos.logback:logback-classic:1.0.7"
}
  ...
}

now, if I want to do anything from the Grails commandline, either grails compile or grails clean, it’s complaining that it couldn’t execute the script because it couldn’t find the LoggerFactory class:

| Loading Grails 2.1.1
| Configuring classpath
| Error Error executing script Compile: org/slf4j/LoggerFactory (NOTE: Stack trace has been filtered. Use --verbose to see entire trace.)
java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:156)
at org.apache.commons.logging.impl.SLF4JLogFactory.getInstance(SLF4JLogFactory.java:132)
at org.apache.commons.logging.LogFactory.getLog(LogFactory.java:272)
at org.springframework.core.io.support.PathMatchingResourcePatternResolver.<clinit>(PathMatchingResourcePatternResolver.java:169)
| Error Error executing script Compile: org/slf4j/LoggerFactory

How can I upgrade the underlying slf4j-api properly?

If I don’t exclude the slf4j-api first, I get a conflict with the “old” 1.6.2 api marked as evicted when calling grails dependency-report…

Also, I’d love to have an external config file for Logback. How would I implement it? With Log4j I just declared a log4jConfigurer bean within the conf/spring/resources.groovy file – how would it be done with Logback?

Has anybody experience in logging Grails 2.1.1 with Logback and could give me any advice for this issue?

Answer 1

As I think that this question would be also a matter of fact for other developers willing to implement the Logback Logging Framework with Grails, I’ll share my progress on the topic within this answer – trying not to overload the initial question with progress information.

1. I still had no luck in updating slf4j within Grails, so I stuck
   with the solution to simply overload the slf4j-api dependency.
   Grails would show no error on grails dependency-report, just an
   “eviction notice” on the older slf4j dependency (1.6.2). This seems
   to work but I’ll keep on searching for a better solution on this
   topic.

2. I’m now able to load an external config file for Logback through
   a ServletContextListener and a ConfigLoader class
   implemented in grails-app/src/java, with the
   ServletContextListener registered within the web.xml file. (to
   get the web.xml simply execute grails install-templates on the
   commandline. You’ll find it under
   grails-app/src/templates/war/web.xml) Be sure to make it the first
   <listener/> entry within your web.xml so that Logback gets
   configured and loaded as soon as possible.

   I found this solution along with the full code sample over at
   https://bowerstudios.com/node/896 which was the best and shortest
   example I found on this topic which seems to work!

   This solution just loaded the external configuration file and used
   it within the ConfigLoader class but didn’t set it for the whole
   Grails application. So I googled around a bit more and I found a
   solution from Logback, available at GitHub (https://github.com/qos-ch/logback-extensions) and integrating with the
   Spring Framework, so I took these classes from this page and
   the LogbackConfigurer class from here and tweaked them to fit
   my needs.

   Now everything works like a charm and I’am able to create an external configuration file and – what I like best – it’s hooking in
   with the log object which is injected to e.g. Controller classes
   by default.

Hope this is also a help for other developers too 😉

If you’ve got a better or more “groovy” solution for this, pleas let me know!