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https://jira.qos.ch/browse/SLF4J-421?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=20254#comment-20254
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Jonathan Esssex commented on SLF4J-421:
---------------------------------------
This is surely a colossal headache for anyone doing much work with Json in
Java...
> LoggerWrapper and subclasses perform argument substitution twice
> -----------------------------------------------------------------
>
> Key: SLF4J-421
> URL: https://jira.qos.ch/browse/SLF4J-421
> Project: SLF4J
> Issue Type: Bug
> Components: slf4j-ext
> Affects Versions: 1.7.x
> Environment: Java 8; haven't tested with earlier versions or Java 9.
> Reporter: Kristin Clemens
> Assignee: SLF4J developers list
> Labels: logging, substitution
> Attachments: log4j2.xml, ReproduceSlf4jExtBug.java, results.txt
>
>
> If a String containing "{}" (alone or with other characters) is passed to a
> LoggerWrapper log method that takes a format string and arguments, or to a
> subclass method that follows the same pattern, a situation can occur where an
> argument is substituted into the place of the argument containing the
> substitution brackets. That argument may be another string preceding the
> string with brackets, or if the string with brackets is first, it may be that
> argument itself.
> This also occurs with log methods following this pattern even when a string
> format message is not expected, such as with XLogger entry and exit methods
> or LoggerWrapper single argument methods.
> It's hard to describe effectively, so I'll provide some examples and test
> cases to help.
> {code:java|title=Brackets Second|borderStyle=solid}
> log.error("{},{}", foo, "[{}]");
> // Expected
> [ERROR] ReproduceSlf4jBug - foo,[{}]
> // Actual
> [ERROR] ReproduceSlf4jBug - foo,[foo]
> {code}
> {code:java|title=Brackets First|borderStyle=solid}
> log.error("{},{}", "[{}]", foo);
> // Expected
> [ERROR] ReproduceSlf4jBug - [{}],foo
> // Actual
> [ERROR] ReproduceSlf4jBug - [[{}]],foo
> {code}
> *In the attached tests, a basic org.slf4j.Logger is tested with the same
> arguments to provide a reference.*
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