Log4j API
Log4j is essentially composed of a logging API called Log4j API, and its reference implementation called Log4j Core.
What is a logging API and a logging implementation?
- Logging API
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A logging API is an interface your code or your dependencies directly logs against. It is required at compile-time. It is implementation agnostic to ensure that your application can write logs, but is not tied to a specific logging implementation. Log4j API, SLF4J, JUL (Java Logging), JCL (Apache Commons Logging), JPL (Java Platform Logging) and JBoss Logging are major logging APIs.
- Logging implementation
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A logging implementation is only required at runtime and can be changed without the need to recompile your software. Log4j Core, JUL (Java Logging), Logback are the most well-known logging implementations.
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Are you looking for a crash course on how to use Log4j in your application or library? See Getting started. You can also check out Installation for the complete installation instructions. |
Starting with version 2.24.0, Log4j API is embraced as the target logging API for both Log4j 2 and Log4j 3.
Hence, Log4j 3 does not contain a Log4j API module, but instead implements "the" Log4j API developed in Log4j 2 branch.
This ensures Log4j 2 users can safely migrate to Log4j 3 without any Log4j API compatibility concerns.