SLF4J 常见错误信息

在本章中，我们将讨论在使用 SLF4J 时遇到的各种错误消息或警告以及这些消息的原因/含义。

问题1：Failed to load class "org.slf4j.impl.StaticLoggerBinder"

这是在类路径中没有提供 SLF4J 绑定时引起的警告。

以下是完整的警告

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.

要解决此问题，您需要添加任一日志记录框架绑定。本教程的《SLF4J 入门程序》一章对此进行了解释。

注意：这发生在 1.6.0 和 1.8.0-beta2 之间的 SLF4J 版本中。

问题2：No SLF4J providers were found

在 slf4j-1.8.0-beta2 中，上面的警告更明确地说“No SLF4J providers are found”。

以下是完整的警告

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.

问题3：Classpath contains SLF4J bindings targeting slf4j-api versions prior to 1.8

如果您使用的是 SLF4J 1.8 版本并且您在类路径中有先前版本的绑定但没有 1.8 的绑定，您将看到如下所示的警告。

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.

问题4：NoClassDefFoundError: org/apache/commons/logging/LogFactory

如果您正在使用slf4j-jcl并且您的类路径中只有slf4j-jcl.jar，您将收到如下所示的异常。

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

要解决此问题，您需要将commons-logging.jar添加到您的类路径中。

问题5：Detected both jcl-over-slf4j.jar AND bound slf4j-jcl.jar on the classpath..

绑定slf4j-jcl.jar将 slf4j 记录器的调用重定向到 JCL，而jcl-over-slf4j.jar将 JCL 记录器的调用重定向到 slf4j。因此，您不能在项目的类路径中同时拥有两者。如果你这样做，你会得到一个例外，例如下面给出的例外。

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

要解决此问题，请删除任一 jar 文件。

问题6：Detected logger name mismatch

您可以通过以下方式创建 Logger 对象：

将要创建的记录器的名称作为参数传递给getLogger()方法。
将类作为参数传递给此方法。

如果您尝试通过将类作为参数传递来创建记录器工厂对象，并且如果您已将系统属性slf4j.detectLoggerNameMismatch设置为 true，那么您作为参数传递给getLogger()方法的类的名称和您使用的类应该相同，否则您将收到以下警告 -

“检测到记录器名称不匹配。

考虑以下示例。

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 yiidian.com");
   }
}

在这里，我们将slf4j.detectLoggerNameMismatch属性设置为 true。我们使用的类的名称是SLF4JExample，我们传递给 getLogger() 方法的类名称是Sample，因为它们不相等，我们将收到以下警告。

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 yiidian.com

注意：这发生在 slf4j 1.7.9 之后

问题7：Classpath contains multiple SLF4J bindings.

类路径中应该只有一个绑定。如果您有多个绑定，您将收到一条警告，列出绑定及其位置。

假设，如果我们在类路径中有绑定slf4j-jdk14.jar和slf4j-nop.jar，我们将收到以下警告。

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]

问题8：Detected both log4j-over-slf4j.jar AND bound slf4j-log4j12.jar on the class path

要将 log4j 记录器调用重定向到 slf4j，您需要使用log4j-over-slf4j.jar绑定，如果要将 slf4j 调用重定向到 log4j，则需要使用slf4j-log4j12.jar绑定。

因此，您不能在类路径中同时拥有两者。如果这样做，您将收到以下异常。

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.

SLF4J 入门程序 SLF4J 参数化日志