Logger not printing with log4j.properties within Spring Boot 1.5.7

Question

I'm using slf4j-api for logging and log4j as a logger. But in my Spring Boot project it doesn't show proper logs with custom log4j settings in log4j.properties .

POM :

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.25</version>
</dependency>

log4j.properties :

# Root logger option
log4j.rootLogger=INFO, stdout

# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

It prints something like:

2018-10-29 13:47:40.601  INFO 7740 --- [nio-8080-exec-1] k.a.o.controller.CustomController     : 2018-08-02 2018-08-04

so, it doesn't show the line where it has been logged. Should I add anything else?

Answer 1

slf4j-api by itself doesn't provide any concrete implementation of logging system. It's a set of interfaces if you wish.

So adding only slf4j-api is not enough.

Logback as was suggested in comments, contains a real implementation of logging system. This library can be imported explicitly of, if you prefer a zero logging configuration, make sure that spring-boot-starter-logging is imported.

So, logback should be used as an alternative to log4j which is also a real implementation of logging system (it also can be used, but frankly speaking logback is superior to log4j1 in terms of functionality, so I don't see any reason to do so).

Once you have logback, the way to set it is to provide a logback.xml file in resources that should contain any configuration you need there.

Answer 2

If you want the default logger to print your desired pattern, you just need to add the following in your application.properties :

logging.pattern.console=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

Spring Boot provides Logback as its default logger. Also adding a logback.xml in your CLASSPATH will allow you to better configure everything else such as Appenders , Patterns etc ( You may do the same through application.properties also ).

As @MarkBrammik already mentions, sl4j is only an abstraction and is therefore not enough. We use sl4j as an interface to utilize other concrete logging APIs such as Logback , log4j , JDK(java.util.logging) , etc.

Additionally, if you want to use log4j , then you will have to add the following dependency in your pom.xml

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-log4j</artifactId>
</dependency>

and then you may further configure it using a log4j.properties placed in your CLASSPATH . If you use log4j you will have to exclude Logback from your Spring dependencies, or else you may get the Class path contains multiple SLF4J bindings error :

<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>

You may check out the link provided below for more info and I hope you will find it useful : https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-logging.html