Apache Log4j 2.9.1 已发布。Log4j 是 Apache 的一个开源项目，通过使用 Log4j
，可以控制日志信息输送的目的地是控制台、文件、GUI 组件、甚至是套接口服务器、NT 的事件记录器、UNIX Syslog
守护进程等。也可以控制每一条日志的输出格式；通过定义每一条日志信息的级别，能够更加细致地控制日志的生成过程。最令人感兴趣的是，这些可以通过一个配置文件来灵活地进行配置，而不需要修改应用的代码。
请注意，从 Log4j 2.9.0 起，Log4j API 已调整为使用 java.util.ServiceLoader 来定位 Log4j 实现。此外，出于安全考虑，SerializedLayout 已被弃用。 Apache Log4j 2.9.1 更新内容： 修复 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.
更改 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 0.11.0.0 to 0.11.0.1.
了解更多可查阅发行说明 下载地址： https://logging.apache.org/log4j/2.x/download.html | 
