Log4j2 學習紀錄

這邊改用 log4j 2.x 版
相同情境改用 2.x 版語法設定

log4j 2.x 相關設定方式

• 情境請參考 Log4j 1.x 學習紀錄

• 設定範例:

  • package insect.totem.school.School;
  • package insect.totem.school.classroom.ClassRoom;
  • Root Logger 資料輸出到 console
  • School 的資料只輸出到 file
  • ClassRoom 的資料只輸出到 email

log4j2.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <Configuration status="WARN">
      <Appenders>
    
        <!-- Console Appender -->
        <Console name="Console" target="SYSTEM_OUT">
          <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n"/>
        </Console>
    
        <!-- File Appender for School -->
        <RollingFile name="SchoolFile" fileName="logs/school.log"
                     filePattern="logs/school-%d{yyyy-MM-dd}-%i.log.gz">
          <PatternLayout>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n</pattern>
          </PatternLayout>
          <Policies>
            <SizeBasedTriggeringPolicy size="1MB"/>
          </Policies>
          <DefaultRolloverStrategy max="3"/>
        </RollingFile>
    
        <!-- SMTP Appender for ClassRoom -->
        <SMTP name="MailAppender"
              subject="Log4j2 Error in ClassRoom"
              to="admin@example.com"
              from="your_email@example.com"
              smtpHost="smtp.example.com"
              smtpUsername="your_email@example.com"
              smtpPassword="your_password"
              bufferSize="512"
              smtpProtocol="smtp"
              smtpPort="25">
          <PatternLayout pattern="%d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n"/>
        </SMTP>
    
      </Appenders>
    
      <Loggers>
    
        <!-- Logger for School -->
        <Logger name="insect.totem.school.School" level="debug" additivity="false">
          <AppenderRef ref="SchoolFile"/>
        </Logger>
    
        <!-- Logger for ClassRoom -->
        <Logger name="insect.totem.school.classroom.ClassRoom" level="error" additivity="false">
          <AppenderRef ref="MailAppender"/>
        </Logger>
    
        <!-- Root Logger -->
        <Root level="info">
          <AppenderRef ref="Console"/>
        </Root>
    
      </Loggers>
    </Configuration>

log4j2.properties

    status = WARN
    name = PropertiesConfig
    
    # ===== Appenders =====
    
    appender.console.type = Console
    appender.console.name = Console
    appender.console.layout.type = PatternLayout
    appender.console.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n
    
    appender.school.type = RollingFile
    appender.school.name = SchoolFile
    appender.school.fileName = logs/school.log
    appender.school.filePattern = logs/school-%d{yyyy-MM-dd}-%i.log.gz
    appender.school.layout.type = PatternLayout
    appender.school.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n
    appender.school.policies.type = Policies
    appender.school.policies.size.type = SizeBasedTriggeringPolicy
    appender.school.policies.size.size = 1MB
    appender.school.strategy.type = DefaultRolloverStrategy
    appender.school.strategy.max = 3
    
    appender.mail.type = SMTP
    appender.mail.name = MailAppender
    appender.mail.subject = Log4j2 Error in ClassRoom
    appender.mail.to = admin@example.com
    appender.mail.from = your_email@example.com
    appender.mail.smtpHost = smtp.example.com
    appender.mail.smtpPort = 25
    appender.mail.smtpProtocol = smtp
    appender.mail.smtpUsername = your_email@example.com
    appender.mail.smtpPassword = your_password
    appender.mail.bufferSize = 512
    appender.mail.layout.type = PatternLayout
    appender.mail.layout.pattern = %d{yyyy-MM-dd HH:mm:ss} [%t] %-5p %c - %m%n
    
    # ===== Loggers =====
    
    logger.school.name = insect.totem.school.School
    logger.school.level = debug
    logger.school.additivity = false
    logger.school.appenderRefs = school
    logger.school.appenderRef.school.ref = SchoolFile
    
    logger.classroom.name = insect.totem.school.classroom.ClassRoom
    logger.classroom.level = error
    logger.classroom.additivity = false
    logger.classroom.appenderRefs = mail
    logger.classroom.appenderRef.mail.ref = MailAppender
    
    # ===== Root Logger =====
    
    rootLogger.level = info
    rootLogger.appenderRefs = console
    rootLogger.appenderRef.console.ref = Console

Log4j 與 log4j2 主要差異

• 這邊整理網路上 Log4j 與 log4j2 間主要差異

分類	Log4j 1.x	Log4j 2.x	差異與說明
效能核心	同步 logging	使用 LMAX Disruptor 高效非同步核心	Log4j 2 的 AsyncAppender 預設支援非同步，多執行緒下性能顯著提升
架構	物件導向但單一類型擴展	Plugin 架構，模組化設計 (Appender/Filter/Layout 可插拔)	使用 @Plugin 註解即可擴充自訂組件
設定檔支援	.properties / .xml	.properties / .xml / .json / .yaml	更彈性，支援 JSON/YAML，且支援熱載入
執行緒	MDC / NDC	ThreadContext(Map / Stack)	支援 Map 與 Stack(比 MDC/NDC 更彈性)， 可跨執行緒傳遞 context
過濾機制	僅 Logger 設等級	Logger、Appender、Marker、ThreadContext 皆可過濾	支援複雜條件組合與過濾器 (如 RegexFilter、ScriptFilter)
非同步	需使用 AsyncAppender	原生支援 Disruptor-based AsyncLoggers(效能最佳)	在大流量 log 場景(如金融、物聯網) 可明顯降低延遲
延遲處理	不支援	支援 lambda 延遲 log 評估	如 logger.debug(() -> "expensive msg")，不執行無意義建構
設定重載	手動重啟	支援自動偵測設定檔變更並重新載入	增加彈性與運維便利性
安全漏洞	重大漏洞 如 Log4Shell	Log4j 2.16+ 修復漏洞並改良 JNDI 行為