最近在使用springboot过程中用到了mybatis-plus ，springboot版本是2.3.1.RELEASE，mybatis-plus 版本3.2.0。
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.2.0</version>
</dependency>使用中需要打印sql日志和参数，网上很多的做法是增加日志输出配置。
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl
加上去后日志确实是出来，可以看到idea控制台上将sql和参数打印出来了。
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@15b67b] was not registered for synchronization because synchronization is not active
JDBC Connection [HikariProxyConnection@6761653 wrapping oracle.jdbc.driver.T4CConnection@1ea226b] will not be managed by Spring
JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?
==> Preparing: SELECT COUNT(1) FROM T_USER_TEST3 WHERE name = ?
==> Parameters: zhangsan3(String)
<== Columns: COUNT(1)
<== Row: 0
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@15b67b]但是项目打成jar包运行后，日志文件上并没有把sql日志记录下来，查看 spring.log文件只看到初始启动日志。
2021-07-22 16:43:26.429 INFO 35468 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '/test'
2021-07-22 16:43:26.456 INFO 35468 --- [main] c.dragonsoft.demojar.DemoJarApplication : Started DemoJarApplication in 21.168 seconds (JVM running for 22.947)
2021-07-22 16:43:45.047 INFO 35468 --- [http-nio-8080-exec-7] o.a.c.c.C.[Tomcat].[localhost].[/test] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-07-22 16:43:45.047 INFO 35468 --- [http-nio-8080-exec-7] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-07-22 16:43:45.062 INFO 35468 --- [http-nio-8080-exec-7] o.s.web.servlet.DispatcherServlet : Completed initialization in 14 ms其实StdOutImpl只是把日志打印到控制台，看下StdOutImpl的源码所在的包，是用System.out.println打印的日志，显然这个是把日志打印到控制台，并不会存到日志文件。
我们知道springboot默认使用的是logback日志组件，mybatis-plus同时提供了slf4j的日志实现，这个正是我们要用的。
修改日志输出方式为slf4j，
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.slf4j.Slf4jImpl
重启再试，日志依然没打印出来，这次连控制台也没有输出sql日志。
通过刚才的日志，我们看到打印sql的实现类是JsqlParserCountOptimize。
JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?跟踪JsqlParserCountOptimize的代码发现，打印日志前有一个判断logger.isDebugEnabled()，
StdOutImpl默认是返回true；
而slf4j，由于没有指定debug日志级别导致日志没有输出，
指定mybatisplus包名下的日志级别为debug。
logging.level.com.baomidou.mybatisplus=DEBUG重启后再试发现日志成功打印出来了，
控制台：
2021-07-22 17:29:52.621 INFO 38796 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '/test'
2021-07-22 17:29:52.642 INFO 38796 --- [ main] c.dragonsoft.demojar.DemoJarApplication : Started DemoJarApplication in 23.164 seconds (JVM running for 24.643)
2021-07-22 17:29:58.715 INFO 38796 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/test] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-07-22 17:29:58.716 INFO 38796 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-07-22 17:29:58.737 INFO 38796 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 21 ms
2021-07-22 17:30:44.025 WARN 38796 --- [l-1 housekeeper] com.zaxxer.hikari.pool.HikariPool : HikariPool-1 - Thread starvation or clock leap detected (housekeeper delta=1m521ms831µs400ns).
2021-07-22 17:30:45.131 DEBUG 38796 --- [nio-8080-exec-1] c.b.m.e.p.p.o.JsqlParserCountOptimize : JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?日志文件：
2021-07-22 17:29:52.621 INFO 38796 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '/test'
2021-07-22 17:29:52.642 INFO 38796 --- [main] c.dragonsoft.demojar.DemoJarApplication : Started DemoJarApplication in 23.164 seconds (JVM running for 24.643)
2021-07-22 17:29:58.715 INFO 38796 --- [http-nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/test] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-07-22 17:29:58.716 INFO 38796 --- [http-nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-07-22 17:29:58.737 INFO 38796 --- [http-nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Completed initialization in 21 ms
2021-07-22 17:30:44.025 WARN 38796 --- [HikariPool-1 housekeeper] com.zaxxer.hikari.pool.HikariPool : HikariPool-1 - Thread starvation or clock leap detected (housekeeper delta=1m521ms831µs400ns).
2021-07-22 17:30:45.131 DEBUG 38796 --- [http-nio-8080-exec-1] c.b.m.e.p.p.o.JsqlParserCountOptimize : JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?但是只是打印了sql，参数呢？通过阅读源码发现参数打印是由logging目录下的这几个类实现的；
具体实现是通过动态代理的方式，
代理的初始化是在org.apache.ibatis.executor.BaseExecutor类进行,可以发现同样有一个debug判断，
查看log实现类，发现项目模块mapper目录没有指定日志级别
修改项目mapper目录日志级别为debug后发现sql日志和参数成功打印。
logging.level.com.dragonsoft.demojar.mapper=DEBUG控制台：
2021-07-22 17:46:29.255 INFO 38688 --- [nio-8080-exec-6] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-07-22 17:46:29.268 INFO 38688 --- [nio-8080-exec-6] o.s.web.servlet.DispatcherServlet : Completed initialization in 13 ms
2021-07-22 17:46:36.869 DEBUG 38688 --- [nio-8080-exec-6] c.b.m.e.p.p.o.JsqlParserCountOptimize : JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?
2021-07-22 17:46:36.906 DEBUG 38688 --- [nio-8080-exec-6] c.d.d.m.U.pagingBySearchable : ==> Preparing: SELECT COUNT(1) FROM T_USER_TEST3 WHERE name = ?
2021-07-22 17:46:36.998 DEBUG 38688 --- [nio-8080-exec-6] c.d.d.m.U.pagingBySearchable : ==> Parameters: zhangsan3(String)日志文件：
2021-07-22 17:46:29.254 INFO 38688 --- [http-nio-8080-exec-6] o.a.c.c.C.[Tomcat].[localhost].[/test] : Initializing Spring DispatcherServlet 'dispatcherServlet'
2021-07-22 17:46:29.255 INFO 38688 --- [http-nio-8080-exec-6] o.s.web.servlet.DispatcherServlet : Initializing Servlet 'dispatcherServlet'
2021-07-22 17:46:29.268 INFO 38688 --- [http-nio-8080-exec-6] o.s.web.servlet.DispatcherServlet : Completed initialization in 13 ms
2021-07-22 17:46:36.869 DEBUG 38688 --- [http-nio-8080-exec-6] c.b.m.e.p.p.o.JsqlParserCountOptimize : JsqlParserCountOptimize sql=SELECT id,password,address,phone,name,email FROM T_USER_TEST3 WHERE name = ?
2021-07-22 17:46:36.906 DEBUG 38688 --- [http-nio-8080-exec-6] c.d.d.m.U.pagingBySearchable : ==> Preparing: SELECT COUNT(1) FROM T_USER_TEST3 WHERE name = ?
2021-07-22 17:46:36.998 DEBUG 38688 --- [http-nio-8080-exec-6] c.d.d.m.U.pagingBySearchable : ==> Parameters: zhangsan3(String)总结：总共需要以下三个配置
1:设置mybatisplus包下的日志级别为DEBUG；
2:设置项目mapper目录的日志级别为DEBUG；
3:设置mybatis-plus的日志输出方式为slf4j。
logging.level.com.baomidou.mybatisplus=DEBUG
#项目mapper目录
logging.level.com.dragonsoft.demojar.mapper=DEBUG
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.slf4j.Slf4jImpl当然，生产环境下还是需要谨慎考虑一下是否开启sql日志，因为日志记录是会进行频繁的IO，会有一定的性能损耗。
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