server:
 port: 8083
 tomcat:
  max-connections: 500
  max-threads: 500
  accesslog:
   enabled: true
   directory: logs/access/
   prefix: access_log
   suffix: .log
   file-date-format: .yyyy-MM-dd
   pattern: "%t [%I] %{X-Forwarded-For}i %l %u %r %s %b %D"

配置文件配置如上，启动spring boot项目，access log日志文件死活不生效，然后又改成properties配置文件格式，

server.port=8081
server.tomcat.accesslog.directory=logs
server.tomcat.accesslog.enabled=true
server.tomcat.accesslog.pattern=common
server.tomcat.accesslog.prefix=access_log
server.tomcat.accesslog.suffix=.log

还是不生效，后面加了tomcat这个basedir立马生效或者server.tomcat.accesslog.directory填写为绝对路径也可生效，完整配置如下：

server:
 port: 8083
 tomcat:
  basedir: 自定义目录
  max-connections: 500
  max-threads: 500
  accesslog:
   enabled: true
   directory: logs/access/ #或者用绝对路径如 /home/app/logs/access，上面的basedir就可以去掉不用了
   prefix: access_log
   suffix: .log
   file-date-format: .yyyy-MM-dd
   pattern: "%t [%I] %{X-Forwarded-For}i %l %u %r %s %b %D"

server.port=8081
server.tomcat.basedir=自定义目录
server.tomcat.accesslog.directory=logs #或者用绝对路径如/home/app/logs/access，用绝对路径后上面的server.tomcat.basedir即可去掉
server.tomcat.accesslog.enabled=true
server.tomcat.accesslog.pattern=common
server.tomcat.accesslog.prefix=access_log
server.tomcat.accesslog.suffix=.log