現在很流行springboot的開發，小編閒來無事也學了學，開發過程中遇見了log4j日誌的一個小小問題，特此記載。

首先在pox.xml中引入對應的maven依賴：

        <!-- 引入log4j-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-log4j</artifactId>
            <version>1.3.8.RELEASE</version>
        </dependency>

然後在src/resources/下新建log4j.properties檔案（摘抄自網上）：

log4j.rootLogger=info,error,CONSOLE,DEBUG
log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender
log4j.appender.CONSOLE.layout=org.apache.log4j.PatternLayout
log4j.appender.CONSOLE.layout.ConversionPattern=%d{yyyy-MM-dd-HH-mm} [%t] [%c] [%p] - %m%n
log4j.logger.info=info
log4j.appender.info=org.apache.log4j.DailyRollingFileAppender
log4j.appender.info.layout=org.apache.log4j.PatternLayout
log4j.appender.info.layout.ConversionPattern=%d{yyyy-MM-dd-HH-mm} [%t] [%c] [%p] - %m%n
log4j.appender.info.datePattern='.'yyyy-MM-dd
log4j.appender.info.Threshold = info
log4j.appender.info.append=true
log4j.appender.info.File=d://springboot3/logs/api_services_info.log
log4j.logger.error=error
log4j.appender.error=org.apache.log4j.DailyRollingFileAppender
log4j.appender.error.layout=org.apache.log4j.PatternLayout
log4j.appender.error.layout.ConversionPattern=%d{yyyy-MM-dd-HH-mm} [%t] [%c] [%p] - %m%n
log4j.appender.error.datePattern='.'yyyy-MM-dd
log4j.appender.error.Threshold = error
log4j.appender.error.append=true
log4j.appender.error.File=d://springboot3/logs/error/api_services_error.log
log4j.logger.DEBUG=DEBUG
log4j.appender.DEBUG=org.apache.log4j.DailyRollingFileAppender
log4j.appender.DEBUG.layout=org.apache.log4j.PatternLayout
log4j.appender.DEBUG.layout.ConversionPattern=%d{yyyy-MM-dd-HH-mm} [%t] [%c] [%p] - %m%n
log4j.appender.DEBUG.datePattern='.'yyyy-MM-dd
log4j.appender.DEBUG.Threshold = DEBUG
log4j.appender.DEBUG.append=true
log4j.appender.DEBUG.File=d://springboot3/logs/debug/api_services_debug.log

　　在application.yml中加入如下配置：

logging:
  config: src/main/resources/log4j.properties

至此，log4j的配置完畢，啟動專案，發現會報錯：

1. SLF4J: Class path contains multiple SLF4J bindings.
2. SLF4J: Found binding in [jar:file:/C:/Users/tony/.m2/repository/ch/qos/logback/logback-classic/1.2.3/logback-classic-1.2.3.jar!/org/slf4j/impl/StaticLoggerBinder.class]
3. SLF4J: Found binding in [jar:file:/C:/Users/tony/.m2/repository/org/slf4j/slf4j-log4j12/1.7.25/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
4. SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
5. SLF4J: Actual binding is of type [ch.qos.logback.classic.util.ContextSelectorStaticBinder]
6. 12:02:26.963 [main] DEBUG org.springframework.boot.devtools.settings.DevToolsSettings - Included patterns for restart : []
7. 12:02:26.969 [main] DEBUG org.springframework.boot.devtools.settings.DevToolsSettings - Excluded patterns for restart : [/spring-boot-actuator/target/classes/, /spring-boot-devtools/target/classes/, /spring-boot/target/classes/, /spring-boot-starter-[\w-]+/, /spring-boot-autoconfigure/target/classes/, /spring-boot-starter/target/classes/]
8. 12:02:26.969 [main] DEBUG org.springframework.boot.devtools.restart.ChangeableUrls - Matching URLs for reloading : [file:/F:/work_intel/code/demo1/target/classes/]
9. Logging system failed to initialize using configuration from 'src/main/resources/log4j.properties'

這是因為與logback的衝突並未解決，導致啟動失敗，根據上面的報錯資訊，找到logback-classic-1.2.3.jar和slf4j-log4j12-1.7.25.jar的相應位置刪除，並在pom.xml中加入如下排除程式碼：

     <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <!-- 排除預設的logback日誌，使用log4j-->
            <exclusions>
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

啟動發現一切正常，至此，log4j的配置完畢。