Slf4j

Internal

• Java

Bindings

SLF4J needs an actual binding to a known logging framework. The binding is executed at runtime by the class org.slf4j.impl.StaticLoggerBinder, which is embedded in biding libraries. If no SLF4J binding library could be found on the class path, you will see "" (see below for more details).

To fix, you need to place one (and only one) of slf4j-nop.jar, slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the classpath.

If you are packaging an application and you do not care about logging, then placing slf4j-nop.jar on the class path of your application will get rid of this warning message. Note that embedded components such as libraries or frameworks should not declare a dependency on any SLF4J binding but only depend on slf4j-api. When a library declares a compile-time dependency on a SLF4J binding, it imposes that binding on the end-user, thus negating SLF4J's purpose.

Troubleshooting

No StaticLoggerBinder

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.

SLF4J needs an actual binding to a known logging framework. The above message means that the binding, provided by org.slf4j.impl.StaticLoggerBinder, was not found, which means that no appropriate SLF4J binding could be found on the class path.

To fix, you need to place one (and only one) of slf4j-nop.jar, slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the classpath.

If you are packaging an application and you do not care about logging, then placing slf4j-nop.jar on the class path of your application will get rid of this warning message. Note that embedded components such as libraries or frameworks should not declare a dependency on any SLF4J binding but only depend on slf4j-api. When a library declares a compile-time dependency on a SLF4J binding, it imposes that binding on the end-user, thus negating SLF4J's purpose.

Multiple SLF4J Bindings

If the classpath contains two or more JARs with SLF4J bindings, we get this:

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/ovidiu/runtime/os-stats-1.0.1-SNAPSHOT-6/lib/slf4j-log4j12-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/ovidiu/runtime/jboss-eap-6.4.6/modules/system/layers/base/org/slf4j/impl/main/slf4j-jboss-logmanager-1.0.3.GA-redhat-1.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.

The solution is to leave only one.

More details:

http://www.slf4j.org/codes.html#multiple_bindings