Slf4j class path contains multiple slf4j bindings как исправить

Class path contains multiple SLF4J bindings is a warning message from the SLF4J library when your project has different SLF4J bindings for the same logging framework in the “$CLASSPATH”.

This article will explain factors that will lead to this warning message, and we’ll teach you methods that can resolve it in your coding environment. From what you’ll learn in the upcoming sections, you’ll learn how to remove multiple slf4j bindings, and you’ll feel confident that you can solve the warning if you see it again.

Now, switch to your IDE, and let’s save you precious debugging time that you can use for something productive.

Why Do You See the Warning About Multiple slf4j Bindings?

You see the warning about multiple SLF4J bindings because your project has different versions of the SLF4J library in the “$CLASSPATH”. This can happen when multiple dependencies pull in their version of SLF4J, and this can cause conflicts and compatibility issues.

– Your Project Has Different Versions of Slf4j

When your project has different versions of the SLF4J library in the class path, that’s when you’ll see the “class path contains multiple slf4j bindings spring-boot” warning. The major cause of this is when your project has multiple dependencies, and each of these dependencies has its version of SLF4J.

This will lead to a wrong class path order and compatibility issues because SLF4J can select another binding and send your logging to another logging framework, causing confusion. For example, if you have two dependencies in your project, one that uses SLF4J version “1.7.25” and another that uses SLF4J version “1.7.26”, this can lead to the warning.

The warning happens because when your application runs, both versions of the SLF4J library will be loaded into the class path. With this, the Java Virtual Machine (JVM) may not know which version to use.

Another example is if your logging framework is configured to use Logback and you have included the SLF4J API in your project as a dependency. Logback will automatically include its binding for SLF4J, and you’ll see the warning if you have another logging framework that includes its binding for SLF4J.

How To Solve the Multiple slf4j Bindings Warning?

To solve the multiple SLF4J bindings warning, you can exclude the conflicting SLF4J library in your build process via the “pom.xml” or “build.gradle”. And if you are running your application from the command line, you can specify the class path using the “-cp” or “-classpath” option.

Additionally, you can set the order of the class path elements or enforce a single SLF4J using the “maven-enforcer-plugin”. Finally, if Gradle is your build system, use “resolutionStrategy” to force a specific version of SLF4J.

– Exclude the Conflicting slf4j Library in Your Build Process

The exclusion of the conflicting SLF4J library in your build process is how you solve the “class path contains multiple slf4j bindings maven” warning message. Before you exclude it, you’ll need to identify the conflicting SLF4J library using the Maven dependency tree.

The latter will display the hierarchical view of your project’s dependencies, including their transitive dependencies and their version numbers. From this, you can see duplicate libraries in your project, and you can exclude them in the “pom.xml” file.

Now to use the Maven dependency tree, use the following steps:

1. Open a terminal or command prompt and navigate to the root directory of your Maven project.
2. Run the following command (without quotes): “mvn dependency:tree”
3. Examine the output of the previous command and look for any SLF4J library dependencies with different versions that may be causing the error.
4. Exclude any duplicate or conflicting dependencies from your build configuration by adding an exclusion to the relevant dependency in your “pom.xml” file.

For example, in the following XML file, the “slf4j-api” dependency is excluded from the “slf4j-log4j12” dependency. This ensures that only one version of the SLF4J library is included in the project’s class path. Also, you can use the same approach to solve the “systemerr r slf4j: class path contains slf4j bindings” in Tomcat or Spring Boot.

– Set the Order of the Class Path Elements

In the context of resolving the “multiple SLF4J bindings” warning, you can adjust the class path order by using the maven-surefire-plugin to set the order of the class path elements. This will exclude unwanted versions of the SLF4J library from the class path during test execution.

You can do this by adding exclusion rules to the plugin configuration in your project’s “pom.xml” file. For example, to exclude version “1.7.26” of the SLF4J library, you can add the following configuration to the Surefire plugin:

– Specify the Classpath Using the “-Cp” or “-Classpath” Option

A solution to the “slf4j: class path contains multiple slf4j bindings pyspark” warning is to explicitly set the class path in your application’s startup script or command. This is a perfect solution for you if you’re running your application from the command line because you can avoid conflicts with other versions of the SLF4J library.

To set the class path, use the “-cp” or “-classpath” option as follows:

java -cp /path/to/correct/slf4j-version.jar:/path/to/other/libs my.package.MainClass

From the command above, note the following:

• The “-cp” flag is used to specify the classpath
• The “/path/to/correct/slf4j-version.jar” directory contains the correct version of the SLF4J library that your application needs.
• The “/path/to/other/libs” directory contains any other libraries that your application needs to run.

Finally, if Eclipse is your IDE, you can solve the “class path contains multiple slf4j bindings. eclipse” warning by removing the SLF4J binding from your project’s class path. You do this using the following: “YourProject > Properties > Java Build Path > Libraries > Select the SLF4J Binding JAR and hit ‘Remove’”.

– Enforce a Single slf4j Using “Maven-enforcer-Plugin

A tool that will solve the “class path contains multiple slf4j bindings” warning is the Maven Enforcer Plugin. You can also use this plugin to ensure that your project includes only one version of the SLF4J library.

To do this, you’ll configure the plugin to fail the building process if multiple versions of the library are detected in your project’s dependencies.

For example, the following configuration in your “pom.xml” file tells the Maven Enforcer Plugin to enforce the use of the “1.7.30” version of the SLF4J library:

– Use “Resolutionstrategy” To Force a Version of Slf4j

If Gradle is your build tool, you can use the “resolutionStrategy” block in “build.gradle” to force a specific version of the SLF4J library. This will solve the “class path contains multiple slf4j bindings gradle IntelliJ warning and get you back on track. Before this, you can use Gradle dependency insight to identify the conflicting SLF4J library:

./gradlew dependencyInsight –dependency slf4j-api

The output of the previous command will allow you to identify which dependencies are causing the conflict. Once you have identified the conflicting dependencies, you can use the “resolutionStrategy” block in the “build.gradle” file to force a specific version of the SLF4J library.

For example, if you want to force version “1.7.30” of the SLF4J library, you can add the following block to your “build.gradle” file:

Conclusion

This article explains why you see multiple SLF4J bindings in a class path and five methods to resolve it for you. As you move on to your daily activities, hold on to the following:

• You’ll see the “class path contains multiple SLF4J bindings” if there are multiple bindings for the same logging framework in the class path.
• You can solve the multiple SLF4J bindings warning by excluding the conflicting SLF4J library from your build process.
• To exclude an SLF4J library in Maven, identify the conflicting library using the “mvn dependency:tree” command and it to the “<exclusion>” block in “pom.xml”.
• The “maven-enforcer-plugin” and the “resolutionStrategy” in Gradle are ways to ensure that your project uses a specific version of SLF4J.
• To solve the “class path contains multiple slf4j bindings docker” warning, you can also exclude the conflicting SLF4J library in “build.gradle” or “pom.xml”.

Now, you should feel good because you have lots of methods that will fix the “multiple SLF4J bindings” warning messages. Have fun, and don’t forget to share our article.

В этой главе мы обсудим различные сообщения об ошибках или предупреждения, которые мы получаем при работе с SLF4J, и причины / значения этих сообщений.

Не удалось загрузить класс “org.slf4j.impl.StaticLoggerBinder”.

Это предупреждение, которое вызывается, если в пути к классам нет привязок SLF4J.

Ниже приводится полное предупреждение –

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.

Чтобы решить эту проблему, необходимо добавить одну из привязок каркаса ведения журнала. Это объясняется в главе Hello World этого урока.

Примечание. Это происходит в версиях SLF4J между 1.6.0 и 1.8.0-бета2.

Поставщики SLF4J не найдены

В slf4j-1.8.0-beta2 вышеупомянутое предупреждение более ясно говорит, что «поставщики SLF4J не были найдены» .

Ниже приводится полное предупреждение –

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 содержит привязки SLF4J для версий slf4j-api до 1.8

Если вы используете версию SLF4J 1.8 и у вас есть привязки предыдущих версий в classpath, но не привязки 1.8, вы увидите предупреждение, как показано ниже.

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

Если вы работаете с slf4j-jcl и у вас есть только slf4j-jcl.jar в вашем пути к классам, вы получите исключение, такое как приведенное ниже.

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

Чтобы решить эту проблему, вам нужно добавить commons-logging.jar к вашему classpath.

Обнаружил как jcl-over-slf4j.jar, так и связанный slf4j-jcl.jar на пути к классам.

Привязка slf4j-jcl.jar перенаправляет вызовы регистратора slf4j в JCL, а jcl-over-slf4j.jar перенаправляет вызовы регистратора JCL в slf4j. Таким образом, вы не можете иметь оба в classpath вашего проекта. Если вы сделаете это, вы получите исключение, такое как приведенное ниже.

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

Чтобы решить эту проблему, удалите любой из файлов JAR.

Обнаружено несоответствие имени регистратора

Вы можете создать объект Logger с помощью –

• Передача имени созданного регистратора в качестве аргумента методу getLogger () .

• Передача класса в качестве аргумента этому методу.

Передача имени созданного регистратора в качестве аргумента методу getLogger () .

Передача класса в качестве аргумента этому методу.

Если вы пытаетесь создать объект фабрики регистратора, передавая класс в качестве аргумента, и если вы установили системное свойство slf4j.detectLoggerNameMismatch в значение true, тогда имя класса, которое вы передаете в качестве аргумента методу getLogger () и используемый вами класс должен быть таким же, в противном случае вы получите следующее предупреждение –

«Обнаружено несоответствие имени регистратора.

Рассмотрим следующий пример.

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");
   }
}

Здесь мы установили для свойства slf4j.detectLoggerNameMismatch значение true. Имя класса, которое мы использовали, – SLF4JExample, а имя класса, которое мы передали методу getLogger (), – Sample, так как они оба не равны, мы получим следующее предупреждение.

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

Примечание – это происходит после slf4j 1.7.9

Classpath содержит несколько привязок SLF4J.

У вас должна быть только одна привязка в пути к классам. Если у вас есть несколько привязок, вы получите предупреждение с указанием привязок и их местоположения.

Предположим, что если у нас есть привязки slf4j-jdk14.jar и slf4j-nop.jar в пути к классам, мы получим следующее предупреждение.

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]

Обнаружены оба log4j-over-slf4j.jar И привязанные slf4j-log4j12.jar на пути к классам

Чтобы перенаправить вызовы log4j logger в slf4j, вам нужно использовать привязку log4j-over-slf4j.jar, а если вы хотите перенаправить вызовы slf4j в log4j, вам необходимо использовать привязку slf4j-log4j12.jar .

Таким образом, вы не можете иметь оба в classpath. Если вы это сделаете, вы получите следующее исключение.