（1） 引包

（注：當排除預設logback日誌時，放spring-boot-starter-web下不能把logback清理乾淨，報Class path contains multiple SLF4J bindings.）

<!-- 發郵件 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-mail</artifactId>
</dependency>
<!-- log related -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter</artifactId>
    <exclusions><!-- 去掉預設log配置 -->
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-logging</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<!-- 引入log4j2依賴 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>
<!-- 支援識別yml配置 -->
<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-yaml</artifactId>
    <version>2.9.7</version>
</dependency>
<!-- 解析yml配置 -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.7</version>
</dependency>
<!-- end of log related -->
 

（2） 在resource下建立log4j2.yml檔案

Configuration:
  appenders:
    Console:
      name: Console
      target: SYSTEM_OUT
      PatternLayout:
        Pattern: "%d{yyyy-MM-dd HH:mm:ss,SSS}:%4p %t (%F:%L) - %m%n"
    RollingFile:
      -
        name: ROLLING_FILE
        ignoreExceptions: false
        fileName: ../logs/log4j2.log
        filePattern: "../logs/log4j2-%d{yyyy-MM-dd}-%i.log"
        PatternLayout:
          Pattern: "%d{yyyy-MM-dd HH:mm:ss,SSS}:%4p %t (%F:%L) - %m%n"
        Policies:
          TimeBasedTriggeringPolicy:
            modulate: true
            interval: 1
          SizeBasedTriggeringPolicy:
            size: 2MB
        DefaultRolloverStrategy:
          max: 20
    SMTP:
      name: Mailer
      subject: ERROR LOG
      to: 
 
[email protected] # 多收件人（以逗號隔開 ****@qq.com,****@163.com）
      from:*****@qq.com
      smtpHost: smtp.qq.com
      smtpPort: 25
      smtpProtocol: smtp
      smtpUsername: *****@qq.com
      smtpPassword: yourpassword
      smtpDebug: false    # 是否開啟發郵件除錯模式
      bufferSize: 1024
#      Async:
#        name: AsyncMailer
#        appender-ref: Mailer
  Loggers:
    root:
      level: INFO
      appender-ref:
        -
          ref: Console
        -
          ref: ROLLING_FILE
    Logger: #單獨設定某些包的輸出級別
      -
        name: org.springframework.web
        additivity: false #去除重複的log
        level: error
        appender-ref:
          -
            ref: Console
          -
            ref: ROLLING_FILE
      -
        name: org.springboot.sample
        additivity: false
        level: error
        appender-ref:
          -
            ref: Console
          -
            ref: ROLLING_FILE
      -
        name: com.alibaba.druid
        additivity: false
        level: error
        appender-ref:
          -
            ref: Console
          -
            ref: ROLLING_FILE
      -
        name: AsyncMailerLogger
        additivity: false
        level: error
        appender-ref:
          -
            ref: Mailer
 

（3） 使用方式：【注：application.yml中就不必設定logger.config了】

private static final Logger LOGGER_MAIL = LoggerFactory.getLogger("AsyncMailerLogger");
LOGGER_MAIL.error("你好！");

總結：

       1. 當把使用方式放spring boot的mian方法下使用時，會直接執行被攔截死，因為bean建立都未完成，直接呼叫肯定失敗。

       2. log4j2與logback的使用：spring boot預設引入logback並提供了需要引用的類上加@Slf4j註解，而log4j2需要在呼叫類中引用（3）中的那段程式碼。