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What is Log4j?
Log4j, first released in 2001 (1.0), is a widely used, open-source logging library/software framework used on servers to track network, application and user activities (e.g. by enterprise security or software teams). It is the most popular logging framework for Java applications – its popularity can be traced back to the Java Development Kit not including logging APIs early on. (Java is one of the most popular programming languages in enterprises – its cross-platform framework enables applications to run on billions of devices and across operating systems such as Windows, Linux, and macOS.) Log4j has been downloaded tens of millions of times, and is used in popular projects/applications like Hadoop, Kafka, Spark, Apple iCloud, Cisco and VMware programs, Steam, and Twitter.