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From "Zilong Song (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LOG4J2-1561) print expected mdc info to each line of the exception stacktrace
Date Sun, 04 Sep 2016 16:03:20 GMT

    [ https://issues.apache.org/jira/browse/LOG4J2-1561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15463122#comment-15463122

Zilong Song commented on LOG4J2-1561:

Hi, thank you for your question. But I didn't quite understand your point. I have 2 kinds
of comprehensions:

1. The existing option already support my requirement, I can do it by just configuring the
pattern layout in log4j2.xml.
2. I can extend the option in %ex (or %xEx) conversion to implement this feature, instead
of providing a new converter.

If the first one is what you mean, would you please show me how to configure the pattern layout?
As far as I learned, I still don't know how to reach this goal. I will appreciate it very
much if you show it to me.

If the second is what you mean, then I think it may be better to provide a new converter.
the existing ThrowablePatternConverters are not very friendly for extension because the format
of the options are very fixed and hard to make compatible modification. and if we are lucky
to successfully make such a modification, the future modifications will be more limited than
this time. Another reason why I not to do it in this way is that the ThrowablePatternConverters
are complex enough, and I do not wish to increase its complexity.

Another way I have considered to reach this goal is to provide a converter like %replace,
so that I can insert the MDC info before the new line character. But I give it up because
it will cost a lot of memory resources. The %replace converter will buffer the contents in
a StringBuilder and then do modification on it when append to the final log event text builder.
As we know the stack traces are always very large (hundreds or even thousands of characters),
a copy of it will cost a lot memory and time. 

So I finally choose to use a new converter to do it.

> print expected mdc info to each line of the exception stacktrace
> ----------------------------------------------------------------
>                 Key: LOG4J2-1561
>                 URL: https://issues.apache.org/jira/browse/LOG4J2-1561
>             Project: Log4j 2
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 2.6.2
>         Environment: OS X EI Caption, Java 1.7
>            Reporter: Zilong Song
>            Priority: Minor
>              Labels: features
>             Fix For: 2.6.2
>   Original Estimate: 12h
>  Remaining Estimate: 12h
> In some applications we need to append certain MDC information to each line of logs for
a certain process, so that we can easily distinguish them from other logs, and do further
analysis. But currently this information cannot be appended to any line of the stack trace,
so it's hard to get the lines of the stack trace from a textual log file with massive lines
of logs. This issue will append this information to each line of the stack trace. 
> An already known usage for this feature is that we can easily get all lines of log for
a certain process when we set an ID before the process starts, including all lines of the
stack trace.
> Following is the code and configuration, and the output of it.
> {code:java|title=Test.main()}
> public static void main(String[] args) {
>     final Logger logger = LogManager.getRootLogger();
>     ThreadContext.put("proc_id", "1234567890");
>     Exception exception = new Exception("sample exception");
>     logger.info("an exception is logged", exception);
> }
> {code}
> {code:xml|title=log4j2.xml|}
> <?xml version="1.0" encoding="UTF-8"?>
> <Configuration status="warn" name="live-im">
>     <Appenders>
>         <Console name="console-log" target="SYSTEM_OUT">
>             <PatternLayout pattern="%d %p [%t] %C{2} (%F:%L) - %m %X{proc_id}%n%cEx{proc_id}"/>
>         </Console>
>     </Appenders>
>     <Loggers>
>         <Root level="all">
>             <AppenderRef ref="console-log"/>
>         </Root>
>     </Loggers>
> </Configuration>
> {code}
> {code:title=output}
> 2016-09-03 22:56:56,721 INFO [main] pattern.Test (Test.java:17) - an exception is logged
> java.lang.Exception: sample exception 1234567890
> 	at org.apache.logging.log4j.core.pattern.Test.main(Test.java:16) [classes/:?] 1234567890
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_91] 1234567890
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_91]
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
~[?:1.8.0_91] 1234567890
> 	at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_91] 1234567890
> 	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144) [idea_rt.jar:?]
> {code}

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