[LOG4J2-3407] PropertiesConfiguration.parseAppender NPE when logger refers to non-existent appender

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 2.17.1
• Fix Version/s: 2.17.2
• Component/s: Log4j 1.2 bridge
• Assignee: Unassigned
• Reporter: Kenny MacLeod
• Created: 18/Feb/22 10:00
• Updated: 30/Mar/22 21:37
• Resolved: 21/Feb/22 16:37

Description

When parsing a log4j.proprties file that contains a logger that refers to a non-existent appender, you get a NPE.

While this is clearly a malformed configuration, Log4j 1.2.x silently ignored this, and the log4j2 bridge should be as tolerant.

Note that PropertiesConfiguration#parseLogger is already tolerant of the appender being missing (it does a null check on the result of parseAppender), but parseAppender itself is not tolerant.

An example config would be:

log4j.logger.mylogger=INFO, myappender
# log4j.appender.myappender=org.apache.log4j.ConsoleAppender

The appender has been commented out, to illustrate the bug.

Stack trace from log4j 2.17.1:

Caused by: java.lang.NullPointerException
		at org.apache.log4j.builders.BuilderManager.parseAppender(BuilderManager.java:72)
		at org.apache.log4j.config.PropertiesConfiguration.parseAppender(PropertiesConfiguration.java:428)
		at org.apache.log4j.config.PropertiesConfiguration.parseLogger(PropertiesConfiguration.java:406)
		at org.apache.log4j.config.PropertiesConfiguration.parseLoggers(PropertiesConfiguration.java:351)
		at org.apache.log4j.config.PropertiesConfiguration.doConfigure(PropertiesConfiguration.java:304)
		at org.apache.log4j.config.PropertiesConfiguration.doConfigure(PropertiesConfiguration.java:93)
		at org.apache.log4j.config.Log4j1Configuration.initialize(Log4j1Configuration.java:60)
		at org.apache.logging.log4j.core.config.AbstractConfiguration.start(AbstractConfiguration.java:293)
		at org.apache.logging.log4j.core.LoggerContext.setConfiguration(LoggerContext.java:626)
		at org.apache.logging.log4j.core.LoggerContext.reconfigure(LoggerContext.java:699)
		at org.apache.logging.log4j.core.LoggerContext.reconfigure(LoggerContext.java:716)
		at org.apache.logging.log4j.core.LoggerContext.start(LoggerContext.java:270)
		at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:155)
		at org.apache.logging.log4j.core.impl.Log4jContextFactory.getContext(Log4jContextFactory.java:47)
		at org.apache.logging.log4j.LogManager.getContext(LogManager.java:196)
		at org.apache.logging.log4j.spi.AbstractLoggerAdapter.getContext(AbstractLoggerAdapter.java:137)
		at org.apache.logging.slf4j.Log4jLoggerFactory.getContext(Log4jLoggerFactory.java:55)
		at org.apache.logging.log4j.spi.AbstractLoggerAdapter.getLogger(AbstractLoggerAdapter.java:47)
		at org.apache.logging.slf4j.Log4jLoggerFactory.getLogger(Log4jLoggerFactory.java:33)
		at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:363)
		at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:388)

Issue Links

• links to: GitHub Pull Request #761