SLF4J - komunikaty o błędach

W tym rozdziale omówimy różne komunikaty o błędach lub ostrzeżenia, które otrzymujemy podczas pracy z SLF4J oraz przyczyny / znaczenie tych komunikatów.

Nie udało się załadować klasy „org.slf4j.impl.StaticLoggerBinder”.

Jest to ostrzeżenie, które pojawia się, gdy w ścieżce klas nie ma żadnych powiązań SLF4J.

Poniżej znajduje się pełne ostrzeżenie -

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.

Aby rozwiązać ten problem, musisz dodać jedno z powiązań struktury rejestrowania. Jest to wyjaśnione wHello world rozdział tego samouczka.

Note - Dzieje się tak w wersjach SLF4J, które są między 1.6.0 a 1.8.0-beta2.

Nie znaleziono dostawców SLF4J

W slf4j-1.8.0-beta2 powyższe ostrzeżenie jest bardziej zrozumiałe “No SLF4J providers were found”.

Poniżej znajduje się pełne ostrzeżenie -

SLF4J: No SLF4J providers were found.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#noProviders for further details.

Classpath zawiera powiązania SLF4J przeznaczone dla wersji slf4j-api wcześniejszych niż 1.8

Jeśli używasz wersji SLF4J 1.8 i masz powiązania poprzednich wersji w ścieżce klas, ale nie powiązania 1.8, zobaczysz ostrzeżenie, jak pokazano poniżej.

SLF4J: No SLF4J providers were found.
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#noProviders for further details.
SLF4J: Class path contains SLF4J bindings targeting slf4j-api versions prior to
1.8.
SLF4J: Ignoring binding found at
[jar:file:/C:/Users/Tutorialspoint/Desktop/Latest%20Tutorials/SLF4J%20Tutorial/
slf4j-1.7.25/slf4j-jdk14-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#ignoredBindings for an explanation.

NoClassDefFoundError: org / apache / commons / logging / LogFactory

Jeśli pracujesz z slf4j-jcl a jeśli masz tylko slf4j-jcl.jar w swojej ścieżce klas otrzymasz wyjątek, taki jak podany poniżej.

Exception in thread "main" java.lang.NoClassDefFoundError:
org/apache/commons/logging/LogFactory
   at org.slf4j.impl.JCLLoggerFactory.getLogger(JCLLoggerFactory.java:77)
   at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:358)
   at SLF4JExample.main(SLF4JExample.java:8)
Caused by: java.lang.ClassNotFoundException:
org.apache.commons.logging.LogFactory
   at java.net.URLClassLoader.findClass(Unknown Source)
   at java.lang.ClassLoader.loadClass(Unknown Source)
   at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
   at java.lang.ClassLoader.loadClass(Unknown Source)
   ... 3 more

Aby rozwiązać ten problem, musisz dodać commons-logging.jar do swojej ścieżki klas.

Wykryto zarówno jcl-over-slf4j.jar, jak i powiązany slf4j-jcl.jar w ścieżce klasy.

Wiązanie slf4j-jcl.jar przekierowuje wywołania loggera slf4j do JCL i jcl-over-slf4j.jarprzekierowuje wywołania loggera JCL do slf4j. Dlatego nie możesz mieć obu w ścieżce klas projektu. Jeśli to zrobisz, otrzymasz wyjątek, taki jak podany poniżej.

SLF4J: Detected both jcl-over-slf4j.jar AND bound slf4j-jcl.jar on the class
path, preempting StackOverflowError.
SLF4J: See also http://www.slf4j.org/codes.html#jclDelegationLoop for more
details.
Exception in thread "main" java.lang.ExceptionInInitializerError
   at org.slf4j.impl.StaticLoggerBinder.<init>(StaticLoggerBinder.java:71)
   at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:42)
   at org.slf4j.LoggerFactory.bind(LoggerFactory.java:150)
   at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:124)
   at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:412)
   at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:357)
   at SLF4JExample.main(SLF4JExample.java:8)
Caused by: java.lang.IllegalStateException: Detected both jcl-over-slf4j.jar
AND bound slf4j-jcl.jar on the class path, preempting StackOverflowError. See
also http://www.slf4j.org/codes.html#jclDelegationLoop for more details.
   at org.slf4j.impl.JCLLoggerFactory.<clinit>(JCLLoggerFactory.java:54)
   ... 7 more

Aby rozwiązać ten problem, usuń jeden z plików jar.

Detected logger name mismatch

You can create a Logger object by −

Passing the name of the logger to be created as an argument to the getLogger() method.
Passing a class as an argument to this method.

If you are trying to create the logger factory object by passing a class as an argument, and if you have set the system property slf4j.detectLoggerNameMismatch to true, then the name of the class you pass as an argument to the getLogger() method and the class you use should be the same otherwise you will receive the following warning −

“Detected logger name mismatch.

Consider the following example.

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class SLF4JExample {
   public static void main(String[] args) {
      System.setProperty("slf4j.detectLoggerNameMismatch", "true");
      
      //Creating the Logger object
      Logger logger = LoggerFactory.getLogger(Sample.class);

      //Logging the information
      logger.info("Hi Welcome to Tutorilspoint");
   }
}

Here, we have set the slf4j.detectLoggerNameMismatch property to true. The name of the class we used is SLF4JExample and the class name we have passed to the getLogger() method is Sample since they both are not equal we will get the following warning.

SLF4J: Detected logger name mismatch. Given name: "Sample"; computed name:
"SLF4JExample".
SLF4J: See http://www.slf4j.org/codes.html#loggerNameMismatch for an
explanation
Dec 10, 2018 12:43:00 PM SLF4JExample main
INFO: Hi Welcome to Tutorilspoint

Note − This occurs after slf4j 1.7.9

Classpath contains multiple SLF4J bindings.

You should have only one binding in the classpath. If you have more than one binding, you will get a warning listing the bindings and the locations of them.

For suppose, if we have the bindings slf4j-jdk14.jar and slf4j-nop.jar in the classpath we will get the following warning.

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in
[jar:file:/C:/Users/Tutorialspoint/Desktop/Latest%20Tutorials/SLF4J%20Tutorial/
slf4j-1.7.25/slf4j-nop-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in
[jar:file:/C:/Users/Tutorialspoint/Desktop/Latest%20Tutorials/SLF4J%20Tutorial/
slf4j-1.7.25/slf4j-jdk14-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an
explanation.
SLF4J: Actual binding is of type [org.slf4j.helpers.NOPLoggerFactory]

Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path

To redirect the log4j logger calls to slf4j, you need to use log4j-over-slf4j.jar binding and if you want to redirect slf4j calls to log4j, you need to use slf4j-log4j12.jar binding.

Therefore, you cannot have both in the classpath. If you do, you will get the following exception.

SLF4J: Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the
class path, preempting StackOverflowError.
SLF4J: See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more
details.
Exception in thread "main" java.lang.ExceptionInInitializerError
   at org.slf4j.impl.StaticLoggerBinder.<init>(StaticLoggerBinder.java:72)
   at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:45)
   at org.slf4j.LoggerFactory.bind(LoggerFactory.java:150)
   at org.slf4j.LoggerFactory.performInitialization(LoggerFactory.java:124)
   at org.slf4j.LoggerFactory.getILoggerFactory(LoggerFactory.java:412)
   at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:357)
   at org.slf4j.LoggerFactory.getLogger(LoggerFactory.java:383)
   at SLF4JExample.main(SLF4JExample.java:8)
Caused by: java.lang.IllegalStateException: Detected both log4j-over-slf4j.jar
AND bound slf4j-log4j12.jar on the class path, preempting StackOverflowError.
See also http://www.slf4j.org/codes.html#log4jDelegationLoop for more details.