====== Log4j2 ======
  * Java 8 Lambda 지원
  * [[https://logging.apache.org/log4j/2.x/manual/garbagefree.html|Garbage Free]]로 GC 를 최소화 했다.
  * 구현과 API를 분리했기 때문에 Slf4j 등으로 쉽게 이전 가능. ''java.util.Logging'', ''Commons logging'' 등과 쉽게 연동.

===== 취약점 =====
  * [[https://www.slf4j.org/log4shell.html|Comments on the log4shell(CVE-2021-44228) vulnerability]] : 자세히 설명하고 있고 다른 logging 프레임워크들에대해서도 설명해줌
  * [[https://www.boho.or.kr/data/secNoticeView.do?bulletin_writing_sequence=36389|Apache Log4j 2 보안 업데이트 권고]]
  * [[https://www.boannews.com/media/view.asp?idx=103443|[긴급] 로그4j 신규 취약점 ‘CVE-2021-45105’과 패치 ‘Log4j 2.17.0’ 나와]]
  * [[https://www.popit.kr/log4j-%eb%b3%b4%ec%95%88-%ec%b7%a8%ec%95%bd%ec%a0%90-%eb%8f%99%ec%9e%91%ec%9b%90%eb%a6%ac-%eb%b0%8f-jenkins-%ec%84%9c%eb%b2%84-%ed%99%95%ec%9d%b8-%eb%b0%a9%eb%b2%95/|log4j 보안 취약점 동작원리 및 jenkins 서버 확인 방법 | Popit]]
  * 최소한 ''2.17.0'' 이상 버전을 사용해야 한다.

===== 의존성 설정 =====
  * [[https://logging.apache.org/log4j/2.0/runtime-dependencies.html|log4j 2 Runtime Dependencies]]
  * [[http://logging.apache.org/log4j/2.x/faq.html#which_jars|Log4j2 FAQ - Which JAR files do I need?]]
<code groovy>
dependencies {
  compile('com.example:example-project:1.0') {
    exclude group: 'log4j', module: 'log4j'
    exclude group: 'org.slf4j', module: 'slf4j-log4j12'
  }
  compile('org.apache.logging.log4j:log4j-core:2.11.2')
  compile('org.apache.logging.log4j:log4j-slf4j-impl:2.11.2')
  compile('org.apache.logging.log4j:log4j-1.2-api:2.11.2')
}
</code>

===== Garbage Free 로 GC 최소화 =====
  * [[http://www.rationaljava.com/2017/10/allocation-free-logging-with-log4j2.html|Rational Java: Allocation free logging with log4j2]]
  * [[https://logging.apache.org/log4j/2.x/manual/garbagefree.html|Garbage Free]]
  * Garbage Free 를 제대로 사용하려면 지원되는 로깅 패턴만 사용해야 한다.

===== Spring Boot with Lob4j 2 =====
  *[[springframework:springboot|SpringBoot]] 와 함께 사용하기
  * [[https://www.callicoder.com/spring-boot-log4j-2-example/|How to use Log4j 2 with Spring Boot]]

===== syslog =====
  * [[linux:syslog|Linux syslog]]
  * [[https://www.baeldung.com/log4j-to-syslog|Writing Log Data to Syslog Using Log4j2 | Baeldung]]


===== log4jna =====
  * https://github.com/dblock/log4jna
  * Log4JNA is a library of native appenders to write into WindowsTM Event Viewer for Log4j 2TM.

===== 참조 =====
  * [[https://www.loggly.com/blog/benchmarking-java-logging-frameworks/|Benchmarking Java logging frameworks | Log Analysis | Log Monitoring by Loggly]]
    * ''Log4j2''의 ''File Appender'' + ''asynchronous logger'' 조합이 성능이 제일 좋다.
  * [[https://www.mkyong.com/logging/apache-log4j-2-tutorials/|Apache Log4j 2 Tutorials – Mkyong.com]]
  * [[https://howtodoinjava.com/log4j2/log4j-2-json-configuration-example/|Log4j 2 JSON Configuration Example - HowToDoInJava]]
  * [[https://www.baeldung.com/java-logging-ndc-log4j|Java Logging with Nested Diagnostic Context (NDC)]]
  * [[https://www.baeldung.com/log4j2-plugins|Log4j 2 Plugins | Baeldung]]
  * [[https://dzone.com/articles/spring-boot-log4j2-setup|Spring Boot Log4J2 Setup - DZone Java]]