Re: [jgroups-dev] Logging and Inheritance

While the line numbers given are for the wrong class in such a case, I'm 
not going to change the way loggers are created because

    * I want to have 1 logger for a protocol, not 2 or more
    * I don't want to break the OO principle of inheritance
    * Showing line numbers is bad, and should *never* be used in
      production as it is very slow to grab the line numbers (throwing a
      random Throwable, catching it and parsing the first line in the
      stack). This may not even work if we use javac without debug options



Amin Abbaspour wrote:
> Hi,
>
> IMHO this is a known issue and that's why it's sometimes recommended 
> to define loggers as 'private static'.
>
> Yes, I noticed this in our runtime and I can send the exact log as is 
> when I get back to work but here is an example:
>
> Suppose these two classes where B extends A:
>
> ~~~ A.java ~~~
> import org.apache.log4j.Logger;
> public class A {
> protected final Logger log = Logger.getLogger(this.getClass());
> protected void a() {
> log.info("I am in parent");
> }
> }
> ~~~ B.java ~~~
> public class B extends A {
> public void b() {
> a();
> log.info("I am in child");
> }
> public static void main(String[] args) {
> new B().b();
> }
> }
> ~~~ log4j.properties ~~~
> log4j.rootLogger=DEBUG,console
> log4j.appender.console=org.apache.log4j.ConsoleAppender
> log4j.appender.console.layout=org.apache.log4j.PatternLayout
> log4j.appender.console.layout.ConversionPattern=[%p] %c:%L - %m%n
> ~~~
>
> So if you run it you'll with log4j-1.2.14 you'll get:
> ---
> [INFO] B:5 - I am in parent
> [INFO] B:4 - I am in child
> ---
>
> But if you make logger as static in A and define a new one in B you'll 
> get:
> ---
> [INFO] A:5 - I am in parent
> [INFO] B:6 - I am in child
> ---
>
> As Galder said, first (current) method brings better call tracking but 
> results in incorrect line numbers using Log4j. It differs from team to 
> team but for me, second method's output is more clear.
>
> Regards,
> Amin
>
> --- On Fri, 10/8/10, Bela Ban <[email protected]> wrote:
>
>> From: Bela Ban <[email protected]>
>> Subject: Re: [jgroups-dev] Logging and Inheritance
>> To: "Amin Abbaspour" <[email protected]>
>> Cc: [email protected]
>> Date: Friday, October 8, 2010, 11:53 AM
>> Can't reproduce this, do you have
>> some sample code which throws
>> exceptions ? I injected a few exceptions, and the line
>> numbers were
>> always correct
>>
>> Amin Abbaspour wrote:
>>> Hi all,
>>>
>>> I believe it's better to define logger in each class
>> rather than using inheritance, i.e.:
>>> private static final Log log =
>> LogFactory.getLog(MyClassName.class);
>>> It's like this in right now (see Protocol.java):
>>>
>>> protected final Log
>> log=LogFactory.getLog(this.getClass());
>>> This adds a small bit of code but prevent incorrect
>> line numbers in log.
>>> With current model one may see a message in UDP:896
>> while logger class is UDP and line number belongs to
>> TP.java.
>>> Of course this means that every log call in TP results
>> in logging via TP logger not the inherited one, which is
>> bearable IMHO.
>>>
>>>    
>> -- 
>> Bela Ban
>> Lead JGroups / JBoss Clustering team
>> JBoss - a division of Red Hat
>>
>>
>
>
>
>

-- 
Bela Ban
Lead JGroups / Clustering Team
JBoss

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