What's the difference between slf4j-log4j12 and log4j-over-slf4j and when should each be used?
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.12</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>log4j-over-slf4j</artifactId>
<version>1.7.12</version>
</dependency>
log4j-over-slf4j
Use this if your code or some libraries you are using uses Log4j directly, but you want to use a different SLF4J binding than Log4j. It will route the Log4j API calls to SLF4J to the binding you choose. You need to remove the Log4j library from your classpath and replace it with this dependency.
slf4j-log4j12
Use this if you want to use the Log4j 1.2 binding for SLF4J.
You shouldn't use both of these libraries at the same time.
Please note also that Log4j 2 has been released.
Related
I use Lombok.
Some time ago when building a project, the compiler started issuing the following message:
Found slf4j-api dependency but no providers were found. Did you mean
to add slf4j-simple? See https://www.slf4j.org/codes.html#noProviders
.
If you follow the link, there is a rather vague comment:
This warning, i.e. not an error, message is reported when no SLF4J
providers could be found on the class path. Placing one (and only one)
of slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar
or logback-classic.jar on the class path should solve the problem.
Note that these providers must target slf4j-api 1.8 or later.
In the absence of a provider, SLF4J will default to a no-operation
(NOP) logger provider.
Please note that slf4j-api version 1.8.x and later use the
ServiceLoader mechanism. Earlier versions relied on the static binder
mechanism which is no longer honored by slf4j-api. Please read the FAQ
entry What has changed in SLF4J version 1.8.0? for further important
details.
If you are responsible for packaging an application and 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 providers but only depend on slf4j-api. When a
library declares a compile-time dependency on a SLF4J provider, it
imposes that provider on the end-user, thus negating SLF4J's purpose.
I have no idea how to do it correctly. If you have an experience, please, explain me how to do it.
As stated in tutorialspoint :
SLF4J stands for Simple Logging Facade for Java. It provides a simple
abstraction of all the logging frameworks. It enables a user to work
with any of the logging frameworks such as Log4j, Logback, JUL
(java.util.logging), etc. using single dependency.
This means that you have to provide a concrete java logging library on your classpath on top of the dependency for SLF4J itself (Example with Maven):
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>2.0.0-alpha0</version>
</dependency>
You will also need to specify the dependency on your preferred logging library. For instance:
For standard jdk1.4 logging :
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-jdk14 -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-jdk14</artifactId>
<version>2.0.0-alpha0</version>
<scope>runtime</scope>
</dependency>
For slf4j-simple logging :
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>2.0.0-alpha0</version>
<scope>runtime</scope>
</dependency>
For log4j logging :
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>2.0.0-alpha0</version>
<scope>runtime</scope>
</dependency>
Refer this Page: http://www.slf4j.org/codes.html#noProviders
You may add either of the following dependencies: Placing one (and only one) of slf4j-nop.jar slf4j-simple.jar, slf4j-log4j12.jar, slf4j-jdk14.jar or logback-classic.jar on the class path should solve the problem
I used "slf4j-simple" maven dependency from https://mvnrepository.com/artifact/org.slf4j/log4j-over-slf4j
This can be due to the version of slf4J API and you are using. try this changing the version like this.
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.25</version>
</dependency>
I have a jar, say a.jar, for which I'd like to enable logging only at INFO level. This jar also depends on another jar, say b.jar, which uses Apache HTTP client. When I run my application, I see a lot of debug output on the screen including stuff from the Apache HTTP client in this format alone, irrespective of what I put in the log4j.properties:
[com.amazonaws.AmazonWebServiceClient] : Internal logging successfully configured to commons logger: true Ignored FQCN: org.apache.commons.logging.impl.SLF4JLocationAwareLog
For the life of me, I'm unable to figure out where the jars are getting their configuration from. Here're things I tried.
1. Added a log4j.properties to only a.jar's main/resources dir
2. Added a log4j.properties to only b.jar's main/resources dir
3. Removed log4j.properties
Please help me with some inputs as to where the logging configuration may be getting picked up from.
Here're pom extracts of a.jar
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.5</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.15</version>
<scope>compile</scope>
</dependency>
Here's the extract for b.jar
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.7</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.7</version>
<scope>compile</scope>
</dependency>
I assume that you mean this “Apache HTTP client”? If so, then your logging configuration for Log4J does not affect the log output of the HttpClient simply because the latter does neither use SLF4J nor Log4J. As you can see from this POM, HttpClient uses Apache Commons Logging for its log output instead.
So your goal is to redirect all Commons Logging output via SLF4J to Log4J. This requires two steps:
Add an SLF4J bridge for Commons Logging.
Make sure that the bridge is used as a replacement for Commons Logging.
The bridge to add is described here. To make sure that the bridge is actually used, I would recommend to exclude the original Commons Logging JAR. You should be able to achieve both steps with the following new/updated dependencies for your project B:
<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<version>4.5.3</version>
<exclusions>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.7.24</version>
</dependency>
I have added the jcl-over-slf4j bridge in the latest SLF4J version 1.7.24 since it seems that your version of SLF4J (1.7.7) doesn’t seem to support Commons Logging 1.2, yet, which might be used by the HttpClient (at least by the one in version 4.5.3).
(Note that I haven’t tested this. But the eventual solution should at least be pretty similar to the described approach.)
Looking at this, it seems like one of the amazon sdk jars is the place this logging configuration would be present in.
It uses apache commons logging and any configuration that you are doing in your project is being done for slf4j and hence is not taking any effect.
I am learning spring web mvc project from online resources, i came across this logger slf4j, and i want to use it in my application.
I don't have any idea on how to add this. what i am thinking is i should remove commons-logging.jar from lib folder, and add another jar file to lib folder, but then i don't know which jar file i should add as there are many jar files present in slf4j.zip that i have downloaded from its official site.
I have searched and read few posts/articles about integrating slf4j but they all were related to maven, and i don't have maven, i simply started working with adding spring framework jars to dynamic web project.
Please tell me how and what files i should add in lib folder for logging purpose. or how to configure the slf4j logger.
thanx folks!!
The official source of information on logging in Spring is the Spring Reference.
If you want to use SLF4J, this document suggests using the following Maven dependencies:
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.0.6.RELEASE</version>
<exclusions>
<exclusion>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>jcl-over-slf4j</artifactId>
<version>1.5.8</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.5.8</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.5.8</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.14</version>
</dependency>
</dependencies>
In other words, you need four .jar files, and you need to make sure that the Commons Logging library is NOT on your classpath.
If you do not use Maven, you can download these .jars from the Maven Central Repository manually. Enter groupId, artifactId and version on that page, press Search, and download the .jar file (not sources.jar!). Here are direct links to these .jar files: jcl-over-slf4j, slf4j-api, slf4j-log4j12, log4j.
You will also need to create and put on your classpath the configuration file for log4j (log4j.xml or log4j.properties).
I think that by not using Maven you make your life harder, not easier. It's better to spend some time learning it, than spend a lot of time trying to avoid learning it.
I would actually argue against using pure SLF4J to begin with, because its own creators have already created a successor.
Reasons to use it instead of SLF4J are given on http://logback.qos.ch/reasonsToSwitch.html
And the "First baby steps" in the manual are at http://logback.qos.ch/manual/introduction.html
I'd like to start using SLF4J with Logback. I read over Logback's online documentation and am now ready to add the JARs to my repo and try it out.
But I'm at a loss! What JARs do I need? I downloaded that latest SLF4J (1.7.5) and expected to see something like slf4j-logback.jar, but don't see anything of the sorts. I've read that Logback contains a "native implementation" of SLF4J, but don't know exactly what this means, or if it also implies that I don't even need slf4j-api-1.7.5.jar on the classpath.
So I ask: to use the latest Logback (1.0.13), what JARs do I need? I took a look at the Maven central repo for logback 1.0.13 and don't see any dependencies listed, so that didn't help me at all. Thanks in advance!
You need to add logback-classic to your pom
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.0.13</version>
</dependency>
it will transitively add the following two:
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.0.13</version>
</dependency>
and
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.5</version>
</dependency>
See https://logback.qos.ch/setup.html#mavenBuild for more information.
I have a Java Maven project whose dependencies include slf4j and its log4j adapter.
I manage the versions of log4j, slf4j-log4j12 and slf4j-api to its newest versions according to http://mvnrepository.com and especially the log4j version of 1.2.17 is well over 1.2.12 but I still get the error
SLF4J: This version of SLF4J requires log4j version 1.2.12 or later.
See also http://www.slf4j.org/codes.html#log4j_version
which is totally unclear to me.
My Maven dependency management looks like this:
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.apache.jena</groupId>
<artifactId>apache-jena-libs</artifactId>
<type>pom</type>
<version>2.10.0</version>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.5</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.5</version>
</dependency>
</dependencies>
</dependencyManagement>
How can I get rid of the warning?
P.S.: I also get a java.lang.NoSuchMethodError: org.apache.log4j.Logger.isTraceEnabled().
P.P.S.: Because of your comments I remembered that the program has a "lib" folder which is not included in the classpath by Maven but by Eclipse itself so the conflicting dependencies must lie there. Sorry, I totally forgot that I guess that's my fault for mixing Maven with a lib folder. I guess I must try to convert as much of the libraries to maven dependencies.
The strange thing though is just that even if I edit "Order and Export" to put the Maven dependencies at the top, the problem still occurs.
StaticLoggerBinder code in slf4j-log4j12 which gets loaded very early on performs a check to determine whether the TRACE level is available in log4j. Here is the code:
private StaticLoggerBinder() {
loggerFactory = new Log4jLoggerFactory();
try {
Level level = Level.TRACE;
} catch (NoSuchFieldError nsfe) {
Util.report("This version of SLF4J requires log4j version 1.2.12 or later."+
" See also http://www.slf4j.org/codes.html#log4j_version");
}
}
It seems pretty airtight to me.
It may be that some other dependency is pulling in or actually embeds an earlier version of log4j. Some *-standalone.jar files are known to do that.
Check your class path at deployment time. Are you deploying in an app server? Is an older version of log4j on the server class path? In a java endorsed path?
You should define the <dependency> outside the <dependencyManagement> as the following: -
<dependencyManagement>
<dependencies>
...
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>org.apache.jena</groupId>
<artifactId>apache-jena-libs</artifactId>
</dependency>
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
</dependency>
</dependencies>
Please see Introduction to the Dependency Mechanism: Dependency Management for further information.
I hope this may help.
Changing comment to answer, since it appeared to solve the issue.
This is a classloader problem, maven built it correctly but is missing
for dependencies. Could you try to provide the missing dependencies to
maven? Otherwise I suggest you look in the Eclipse specific
dependencies.