Java - Slf4j
About
slf4j 1)) is a façade for loggers.
To use a specific logger, add one of the binding logger package.
Dependency
Library should declare a runtime dependency only on on slf4j-api and not on any SLF4J binding but only
dependencies {
runtime 'org.slf4j:slf4j-api:1.7.25'
}
Disable
To disable SLF4J when you have it as transitive dependency, add the NOP binding as runtime dependency.
Example with Gradle
dependencies {
implementation 'org.slf4j:slf4j-nop:1.7.30'
}
Usage
- get a logger
static Logger LOGGER = LoggerFactory.getLogger(MyClass.class);
Concept
Marker sqlMarker = MarkerFactory.getMarker("SQL");
// This is a sql message
logger.debug(sqlMarker ,"SELECT * FROM {}", table);
- Mdc
MDC.put("userId", 128746);
Binding
To switch of logging frameworks, just replace the below jar bindings as dependencies (in the classpath)
- NOP - slf4j-nop-1.7.28.jar NOP - Nothing (No Operation)
-
- version 1.2: - slf4j-log4j12-1.7.28.jar + log4j.jar
- version 2: log4j-slf4j-impl + log4j.jar
- java.util.logging - slf4j-jdk14-1.7.28.jar
- Simple - slf4j-simple-1.7.28.jar - Simple implementation for small app, outputs all events to System.err. Only messages of level INFO and higher are printed.
- Jakarta Commons Logging - slf4j-jcl-1.7.28.jar
- logback - logback-classic-1.2.3.jar (requires logback-core-1.2.3.jar)
How To
How to suppress the error message when you are not using SLF4J
Even if you don't use SLF4J as a logging system, you may have it in your application as transitive dependency (a dependency of your dependency) and you will get this error when starting your application.
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
To suppress this message, if you don't want to use SLF4, add the NOP binding as a dependency.
Example with Gradle
dependencies {
runtime 'org.slf4j:slf4j-nop:1.7.30'
}
How to suppress any log
Because slf4j is just a façade (a wrapper), you need to set the log level on your chosen logger.
For instance, with the JDK logger, if you want to disable the log from a library such as thymeleaf because you know that may get an error, you would do it this way:
Logger logger = Logger.getLogger(org.thymeleaf.TemplateEngine.class.getName());
logger.setLevel(Level.OFF);
Just check which implementation you have chosen to show slf4j logs.