背景
最近在一个Boot应用中使用一个SDK包时候发现这个SDK包中的日志打印不出来，经过结合其源码的调试，发现到了日志打印行执行了，但确实没有打印到控制台，基本断定是日志配置问题。
冲突原因
Boot应用中的日志配置有 log4j.properties，但没有在pom文件中添加log4j的依赖和web的排除，相当于失效了，打印日志还是按默认的打印，而SDK包中代码理使用的是log4j的使用方式，这样就导致Boot应用打印不出SDK包中的日志信息；
解决过程
默认打印日志格式：
2020-03-09 09:36:54.720 INFO 39140 --- [ restartedMain] o.s.c.support.DefaultLifecycleProcessor : Starting beans in phase 0
2020-03-09 09:36:54.725 INFO 39140 --- [ restartedMain] o.s.c.n.eureka.InstanceInfoFactory : Setting initial instance status as: STARTING
2020-03-09 09:36:55.526 INFO 39140 --- [ restartedMain] o.s.c.n.e.s.EurekaServiceRegistry : Registering application adms-query-service with eureka with status UP
2020-03-09 09:36:55.578 INFO 39140 --- [ restartedMain] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8082 (http)
2020-03-09 09:36:55.579 INFO 39140 --- [ restartedMain] .s.c.n.e.s.EurekaAutoServiceRegistration : Updating port to 8082
2020-03-09 09:36:55.582 INFO 39140 --- [ restartedMain] c.c.c.r.a.AdmsQueryServiceApplication : Started AdmsQueryServiceApplication in 6.992 seconds (JVM running for 8.427)
2020-03-09 09:37:21.723 INFO 39140 --- [nio-8082-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization started
2020-03-09 09:37:21.750 INFO 39140 --- [nio-8082-exec-1] o.s.web.servlet.DispatcherServlet : FrameworkServlet 'dispatcherServlet': initialization completed in 27 ms
2020-03-09 09:37:21.790 INFO 39140 --- [nio-8082-exec-1] c.c.c.r.a.c.PadLifeQueryController : uid=CMBFRT---signature=ddd0ea7f5f16175720ce72c6699edf34
2020-03-09 09:37:21.834 INFO 39140 --- [nio-8082-exec-1] c.c.c.r.a.c.PadLifeQueryController : 请求入参：{"ctfNbr":"100000000000000001","ctfCod":"01"}
在Boot应用进行了Log4j的依赖定义，pom依赖：
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-log4j</artifactId>
<version>1.3.8.RELEASE</version>
</dependency>
添加后的打印日志已经按log4j.properties定义的进行打印，以[INFO ]为前缀打印info级别日志：
method:org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainer.start(TomcatEmbeddedServletContainer.java:201)Tomcat started on port(s): 8082 (http)
[INFO ] 2020-03-09 09:40:13,326 method:org.springframework.cloud.netflix.eureka.serviceregistry.EurekaAutoServiceRegistration.onApplicationEvent(EurekaAutoServiceRegistration.java:124)Updating port to 8082
[INFO ] 2020-03-09 09:40:13,329 method:org.springframework.boot.StartupInfoLogger.logStarted(StartupInfoLogger.java:57)Started AdmsQueryServiceApplication in 6.726 seconds (JVM running for 8.02)
[INFO ] 2020-03-09 09:40:13,345 method:com.netflix.discovery.DiscoveryClient.register(DiscoveryClient.java:813)DiscoveryClient_ADMS-QUERY-SERVICE/80374563-ZDY.itc.cmbchina.cn:adms-query-service:8082 - registration status: 204
[INFO ] 2020-03-09 09:40:29,485 method:org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:489)FrameworkServlet 'dispatcherServlet': initialization started
[INFO ] 2020-03-09 09:40:29,510 method:org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:508)FrameworkServlet 'dispatcherServlet': initialization completed in 25 ms
相关log配置
springboot默认日志：Logback
日志格式：
时间日期：精确到毫秒
日志级别：ERROR, WARN, INFO, DEBUG or TRACE
进程ID
分隔符：--- 标识实际日志的开始
线程名：方括号括起来（可能会截断控制台输出）
Logger名：通常使用源代码的类名
日志内容
springboot中的jar依赖
spring-boot-starter中spring-boot-starter-logging
日志配置文件
Springboot下自定义日志配置，不同的日志系统，可以按如下规则组织配置文件名：
Logback：logback-spring.xml, logback-spring.groovy, logback.xml, logback.groovy
Log4j：log4j-spring.properties, log4j-spring.xml, log4j.properties, log4j.xml
Log4j2：log4j2-spring.xml, log4j2.xml
JDK (Java Util Logging)：logging.properties
