Spring应用SLF4J日志未在控制台显示问题求助

在Spring Boot应用中使用SLF4J Logger打印DEBUG日志，但控制台看不到自定义的DEBUG日志内容，以下是相关代码、日志、配置及依赖信息：

应用类代码 #

@SpringBootApplication
public class InternalReplacerServiceApplication {
public static void main(String[] args) {
    SpringApplication.run(InternalReplacerServiceApplication.class, args);
    Logger LOG = LoggerFactory.getLogger(InternalReplacerServiceApplication.class);
    LOG.debug("inside app");
}
}

运行时控制台日志 #

2022-08-29 13:00:21.570  INFO 17420 --- [  restartedMain] c.j.j.InternalReplacerServiceApplication : Starting InternalReplacerServiceApplication using Java 17.0.4 on W10-lTkFoL0JX1t with PID 17420 (C:\Users\wgupta\Backend\internal_replacer_service\target\classes started by wgupta in C:\Users\wgupta\Backend\internal_replacer_service)
2022-08-29 13:00:21.572  INFO 17420 --- [  restartedMain] c.j.j.InternalReplacerServiceApplication : No active profile set, falling back to 1 default profile: "default"
2022-08-29 13:00:21.648  INFO 17420 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
2022-08-29 13:00:21.648  INFO 17420 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
2022-08-29 13:00:22.480  INFO 17420 --- [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Multiple Spring Data modules found, entering strict repository configuration mode
2022-08-29 13:00:22.484  INFO 17420 --- [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data Redis repositories in DEFAULT mode.
2022-08-29 13:00:22.519  INFO 17420 --- [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 15 ms. Found 0 Redis repository interfaces.
2022-08-29 13:00:23.409  INFO 17420 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8081 (http)
2022-08-29 13:00:23.430  INFO 17420 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2022-08-29 13:00:23.431  INFO 17420 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.64]
2022-08-29 13:00:23.559  INFO 17420 --- [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2022-08-29 13:00:23.559  INFO 17420 --- [  restartedMain] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 1910 ms
2022-08-29 13:00:24.807  INFO 17420 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2022-08-29 13:00:24.861  INFO 17420 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8081 (http) with context path ''
2022-08-29 13:00:24.879  INFO 17420 --- [  restartedMain] c.j.j.InternalReplacerServiceApplication : Started InternalReplacerServiceApplication in 3.832 seconds (JVM running for 4.524)

application.properties配置 #

server.port=8081
# Redis Config
spring.cache.type=redis
spring.redis.host=127.0.0.1
spring.redis.port=6379

pom.xml依赖 #

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-data-redis</artifactId>
    </dependency>
    <dependency>
        <groupId>redis.clients</groupId>
        <artifactId>jedis</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>

    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-devtools</artifactId>
        <scope>runtime</scope>
        <optional>true</optional>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-test</artifactId>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>io.lindstrom</groupId>
        <artifactId>m3u8-parser</artifactId>
        <version>0.22</version>
    </dependency>
    <dependency>
        <groupId>org.springframework.kafka</groupId>
        <artifactId>spring-kafka</artifactId>
    </dependency>
    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20180813</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        </dependency>
    <!--    Parameter names -->
    <dependency>
        <groupId>com.fasterxml.jackson.module</groupId>
        <artifactId>jackson-module-parameter-names</artifactId>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.datatype</groupId>
        <artifactId>jackson-datatype-jsr310</artifactId>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.datatype</groupId>
        <artifactId>jackson-datatype-jdk8</artifactId>
    </dependency>
</dependencies>

排查原因及解决方案 #

核心原因 #

Spring Boot默认的日志级别是INFO，低于INFO级别的DEBUG日志会被默认过滤，所以控制台看不到自定义的DEBUG日志。另外代码中Logger的初始化位置不够规范，但不是导致日志不输出的直接原因。

解决方案 #

1. 配置DEBUG日志级别
   在application.properties中添加日志级别配置，指定你的类所在包或具体类的日志级别为DEBUG：

# 配置目标类所在包的日志级别为DEBUG
logging.level.c.j.j=DEBUG
# 或者精准配置到单个类
# logging.level.c.j.j.InternalReplacerServiceApplication=DEBUG

如果需要全局开启DEBUG日志（不推荐，会输出大量框架内部日志），可以配置：

logging.level.root=DEBUG

2. 规范Logger初始化（可选）
   将Logger声明为类的静态成员，避免在方法内局部初始化：

@SpringBootApplication
public class InternalReplacerServiceApplication {
    private static final Logger LOG = LoggerFactory.getLogger(InternalReplacerServiceApplication.class);

    public static void main(String[] args) {
        SpringApplication.run(InternalReplacerServiceApplication.class, args);
        LOG.debug("inside app");
    }
}

内容的提问来源于stack exchange，提问作者WISHY