ppkarwasz commented on code in PR #2381: URL: https://github.com/apache/logging-log4j2/pull/2381#discussion_r1662583010
########## src/changelog/.2.x.x/2363_add_logback_throwable_consuming_semantics.xml: ########## @@ -1,8 +1,8 @@ <?xml version="1.0" encoding="UTF-8"?> <entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"; - xmlns="http://logging.apache.org/log4j/changelog"; - xsi:schemaLocation="http://logging.apache.org/log4j/changelog https://logging.apache.org/log4j/changelog-0.1.3.xsd"; - type="added"> + xmlns="https://logging.apache.org/xml/ns"; + xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"; + type="changed"> Review Comment: Nice catch! It is a copy/paste error. Fixed in 42b5ebbb41b4b23f665d395833a10c431a2a602f. ########## src/site/antora/modules/ROOT/examples/migrate-from-logback/MigrateFromLogback.java: ########## @@ -0,0 +1,28 @@ +package example; + +import org.apache.logging.log4j.LogManager; +import org.apache.logging.log4j.Logger; + +class MigrateFromLogback { + private static Logger logger = LogManager.getLogger(); + + doLogWrong() { + try { + // do something + // tag::wrong[] + } catch (Exception e) { Review Comment: Fixed in 42b5ebbb41b4b23f665d395833a10c431a2a602f. ########## src/site/antora/modules/ROOT/pages/migrate-from-logback.adoc: ########## @@ -106,3 +106,62 @@ To assist with migrating Logback configuration components to Log4j Core, see the * xref:manual/filters.adoc[] For the complete list of all Log4j configuration knobs, see xref:manual/configuration.adoc[the Configuration page]. + +[#parameterized-logging] +=== Parameterized logging + +A common mistake in parameterized logging is to add a `{}` placeholder for the exception associated with a log event: + +[source,java,indent=0] +---- +include::example$migrate-from-logback/MigrateFromLogback.java[tag=wrong] +---- + +Log4j Core and Logback differ in the way they treat this statement: + +Logback:: +Logback interprets the `e` argument as throwable and removes it from the list of parameters. +We end up with a parameterized statement with one placeholder, but zero parameters. +The placeholder therefore remains as is: ++ +[source] +---- +The foo process exited with and error: {} +java.lang.RuntimeException: Message + at example.MigrateFromLogback.doLogWrong(MigrateFromLogback.java:10) +... +---- + +Log4j Core:: +Log4j Core first looks for the parameters of the message. +Since the format string has one placeholder, the `e` argument is interpreted as a parameter of the log message. +The throwable associated to the log event is `null`, which results in a missing stack trace: ++ +[source] +---- +The foo process exited with and error: java.lang.RuntimeException: Message +---- + +To fix this problem and obtain the same output in both backends, you should remove the placeholder from the format string: + +[source,java,indent=0] +---- +include::example$migrate-from-logback/MigrateFromLogback.java[tag=right] +---- + +After the change, the output will look us: + +[source] +---- +The foo process exited with and error. +java.lang.RuntimeException: Message + at example.MigrateFromLogback.doLogWrong(MigrateFromLogback.java:10) +... +---- + +[TIP] +==== Review Comment: Fixed in 42b5ebbb41b4b23f665d395833a10c431a2a602f. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
