[logback-dev] [JIRA] Commented: (LBCLASSIC-212) Logback classic doesn't work with Tomcat

[Grzegorz Borkowski (JIRA)]

    [ http://jira.qos.ch/browse/LBCLASSIC-212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=11790#action_11790 ] 

Grzegorz Borkowski commented on LBCLASSIC-212:
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For unknown reasons, I haven't got any mail notification about activity on this issue, despite the fact that I'm reporter of this issue (and watcher too), until today when I got direct mail from Ceki - that's why I thought that nobody looked at this issue yet.
I was able to kind of fix this problem by adding one line of code: in the ExceptionHandler class that handles all exceptions thrown in application (it's spring application, so it is a class declared as exception handler in spring config), I added this line:
log.error(ex.getMessage(), ex);

Earlier, we haven't logged the exception in our code. So my guess was that earlier the exceptions propagated to tomcat, which tried to log the stack trace, which could cause loading some classes, and because of some classloader issues the class was not found, which caused trhowing again the exception, which was tried to be logged by tomcat, and endless loop happened. After adding this line, the error was logged by application, so loading of required class happened in application classloader, and class was found. 
But it's just the guess. The really really big stack trace that I was able to see suggested the endless loop, but in case of endless loop CPU usage should be high, but it wasn't, which would suggest rather kind of deadlock. 
If I have time (which I can't guarantee) I can try to reproduce it by deleting this line and attach the project source, if I succeed.

> Logback classic doesn't work with Tomcat
> ----------------------------------------
>
>                 Key: LBCLASSIC-212
>                 URL: http://jira.qos.ch/browse/LBCLASSIC-212
>             Project: logback-classic
>          Issue Type: Bug
>    Affects Versions: 0.9.21
>            Reporter: Grzegorz Borkowski
>            Assignee: Logback dev list
>            Priority: Critical
>
> We have a web application running on Tomcat 6.0.26, which uses SLF4J for logging. Until now, we used SLF4J-Simple, and it worked very well. Now we try to switch to Logback, but we are not able to make it work. It works for logging one-line messages. But whenever any exception is thrown on server, which should print a stack trace, server hangs (It doesn't matter whether we actually print the stack trace in log or not). From what I was able to observe, it looks like it falls into endless loop, throwing "ClassNotFoundException: ch.qos.logback.classic.spi.ThrowableProxyUtil", which is caught and tried to be logged, which throws this exception again, and so on. I don't know why it throws this ClassNotFoundException - perhaps classloader issue? But even copying the logback jars to Tomcat's lib directory, I'm not able to run the application: than it has problems with starting up. Sometimes it freezes during loading web app, and often it helps to attach and detach debugger to Tomcat - it's a kind of magic... Anyway, it's horrendously painful, and I'm not able to make it work. Why such common setup (webapp on Tomcat) is not described in Logback documentation???
> This is our configuration file :
> <configuration scan="true">
>   <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
>     <!-- encoders are assigned the type
>          ch.qos.logback.classic.encoder.PatternLayoutEncoder by default -->
>     <encoder>
>       <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n%ex</pattern>
>     </encoder>
>   </appender>
>   <root level="info">
>     <appender-ref ref="STDOUT" />
>   </root>
> </configuration>
>  (changing scan to "false" doesn't help. Also changing pattern  to  the one not containing "%ex" doesn't help)
> This is part of pom file related to logging:
>          <dependency>
>             <groupId>org.slf4j</groupId>
>             <artifactId>slf4j-api</artifactId>
>             <version>1.6.0</version>
>         </dependency>
>         <dependency>
>             <groupId>ch.qos.logback</groupId>
>             <artifactId>logback-classic</artifactId>
>             <version>0.9.21</version>
>             <scope>runtime</scope>
>         </dependency>
>         <!-- prevent JCL bundling into final WAR by using scope="provided" -->
>         <dependency>
>             <groupId>commons-logging</groupId>
>             <artifactId>commons-logging</artifactId>
>             <version>1.1.1</version>
>             <scope>provided</scope>
>         </dependency>
>         <!-- use this as adpater to satisfy dependencies on JCL -->
>         <dependency>
>             <groupId>org.slf4j</groupId>
>             <artifactId>jcl-over-slf4j</artifactId>
>             <version>1.6.0</version>
>         </dependency>
> If  we change dependency from logback to SLF4J simple (1.6.0) than everything works smoothly, stacktraces are printed to console, no freezing, everything is perfect.

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