Apache Logging Services

Friday September 22, 2017

Log4j 2.9.1 released

The Apache Log4j 2 team is pleased to announce the Log4j 2.9.1 release!

Apache Log4j is a well known framework for logging application behavior. Log4j 2 is an upgrade to Log4j that provides significant improvements over its predecessor, Log4j 1.x, and provides many other modern features such as support for Markers, lambda expressions for lazy logging, property substitution using Lookups, multiple patterns on a PatternLayout and asynchronous Loggers. Another notable Log4j 2 feature is the ability to be "garbage-free" (avoid allocating temporary objects) while logging. In addition, Log4j 2 will not lose events while reconfiguring.

This release contains bugfixes and minor enhancements.

As of Log4j 2.9.0, the Log4j API was modified to use java.util.ServiceLoader to locate Log4j implementations, although the former binding mechanism is still supported. The Log4j jar is now a multi-release jar to provide implementations of the Java 9 specific classes. Multi-release jars are not supported by the OSGi specification so OSGi modules will not be able to take advantage of these implementations but will not lose functionality as they will fall back to the implementations used in Java 7 and 8. More details on the new features and fixes are itemized below.

Note that subsequent to the 2.9 release, for security reasons, SerializedLayout is deprecated and no longer used as default in the Socket and JMS appenders. SerializedLayout can still be used as before, but has to be specified explicitly. To retain old behaviour, you have to change configuration like:

  <Socket name="socket" host="localhost" port="9500"/>


  <Socket name="socket" host="localhost" port="9500">

We do, however, discourage the use of SerializedLayout and recommend JsonLayout as a replacement:

  <Socket name="socket" host="localhost" port="9500">
    <JsonLayout properties="true"/>

Note that subsequent to the 2.9 release, for security reasons, Log4j does not process DTD in XML files. If you used DTD for including snippets, you have to use XInclude or Composite Configuration instead.

The Log4j 2.9.1 API, as well as many core components, maintains binary compatibility with previous releases.

GA Release 2.9.1

Changes in this version include:

Fixed Bugs

  • LOG4J2-1988: Prevent ConcurrentModificationException with AsyncLoggerConfig.
  • LOG4J2-1914: Prevent ConcurrentModificationException with AsyncLoggerConfig.
  • LOG4J2-2048: Increase default queue size for AsyncAppender from 128 to 1024.
  • LOG4J2-2035: Fix documentation to clarify disruptor-3.3.4 is now required for async loggers (previously the docs referred to disruptor-3.3.3 which was never released).
  • LOG4J2-2030: Inspect all known ClassLoaders to locate the service provider.
  • LOG4J2-2028: Java 9 StackLocator was not properly skipping the initial stack frames. Thanks to Jason Tedor.
  • LOG4J2-2026: java.lang.AbstractMethodError: javax.xml.parsers.DocumentBuilderFactory.setFeature(). Thanks to Leon Finker.
  • LOG4J2-2029: Marker examples should not use deprecated flow APIs. Thanks to Fabrizio Cucci.
  • LOG4J2-1936: ClassNotFoundException when making all loggers asynchronous under OSGi environment. Thanks to Helber Belmiro.


  • LOG4J2-2023: Use a class' canonical name instead of name to create its logger name.
  • LOG4J2-2043: Update Jackson from 2.9.0 to 2.9.1 (fix for Java 9.)
  • LOG4J2-2044: Update Apache Commons CSV from 1.4 to 1.5.
  • LOG4J2-2045: Update javax.mail from 1.5.6 to 1.6.0.
  • LOG4J2-2046: Update Apache Commons Compress from 1.13 to 1.14.
  • LOG4J2-2047: Update Cassandra driver from 3.1.0 to 3.1.4.
  • LOG4J2-2049: Update Apache Kafka Client from to

Apache Log4j 2.9.1 requires a minimum of Java 7 to build and run. Log4j 2.3 was the last release that supported Java 6.

Basic compatibility with Log4j 1.x is provided through the log4j-1.2-api component, however it does not implement some of the very implementation specific classes and methods. The package names and Maven groupId have been changed to org.apache.logging.log4j to avoid any conflicts with log4j 1.x.

For complete information on Apache Log4j 2, including instructions on how to submit bug reports, patches, or suggestions for improvement, see the Apache Apache Log4j 2 website:



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