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https://issues.apache.org/jira/browse/LOG4J2-1793?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15829617#comment-15829617
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Remko Popma edited comment on LOG4J2-1793 at 1/19/17 9:50 AM:
--------------------------------------------------------------
Looking at your screenshot, the exception has itself as the cause:
{code}
thrown= {ArithmeticException@2101} "java.lang.ArithmeticException: / by zero"
cause= {ArithmeticException@2101} "java.lang.ArithmeticException: / by zero"
<- exception has itself as the cause...
cause= {ArithmeticException@2101} "java.lang.ArithmeticException: / by
zero"
...
{code}
So the cause of the exception is the exception itself. This is a circular
reference.
When printing the stack trace of such an exception you need to take special
care to prevent getting caught in an eternal loop.
For example, the JDK
{{[java.lang.Throwable|http://www.docjar.com/html/api/java/lang/Throwable.java.htm]}}
(line 645-710) uses an IdentityHashSet to prevent an eternal loop.
Similarly, Log4j's
{{[ThrowableProxy|https://github.com/apache/logging-log4j2/blob/master/log4j-core/src/main/java/org/apache/logging/log4j/core/impl/ThrowableProxy.java#L131]}}
uses a HashSet to track previously visited {{cause}} exceptions to prevent an
eternal loop.
was (Author: rem...@yahoo.com):
Looking at your screenshot, the exception has itself as the cause:
{code}
thrown= {ArithmeticException@2101} "java.lang.ArithmeticException: / by zero"
cause= {ArithmeticException@2101} "java.lang.ArithmeticException: / by zero"
<- exception has itself as the cause...
cause= {ArithmeticException@2101} "java.lang.ArithmeticException: / by
zero"
...
{code}
So the cause of the exception is the exception itself. This is a circular
reference.
When logging such an exception you need to take special care to prevent getting
caught in an eternal loop.
For example, the JDK
{{[java.lang.Throwable|http://www.docjar.com/html/api/java/lang/Throwable.java.htm]}}
(line 645-710) uses an IdentityHashSet to prevent an eternal loop.
Similarly, Log4j's
{{[ThrowableProxy|https://github.com/apache/logging-log4j2/blob/master/log4j-core/src/main/java/org/apache/logging/log4j/core/impl/ThrowableProxy.java#L131]}}
uses a HashSet to track previously visited {{cause}} exceptions to prevent an
eternal loop.
> Why there can't get thrown from LogEvent
> ----------------------------------------
>
> Key: LOG4J2-1793
> URL: https://issues.apache.org/jira/browse/LOG4J2-1793
> Project: Log4j 2
> Issue Type: Bug
> Components: Core
> Affects Versions: 2.7
> Environment: JDK1.8, CentOS6
> Reporter: elkan
> Labels: patch
> Original Estimate: 48h
> Remaining Estimate: 48h
>
> There I want create a customer defined appender and need get stack case
> message. So in over write append method when implements AbstractAppender,
> then use the function like below code:
> logEvent.getThrown().getCause()
> http://77l54p.com1.z0.glb.clouddn.com/qq20170119142117-log4j2-debug.png-alias
> (Debug Info)
> But it very interesting, it out put null, but I use Eclipse debug enter it
> can get message and seems it were drop-dead halt. Is it a bug problem. There
> need you help, thanks.
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