How to get SLF4J "Hello World" working with log4j?

Question

The "Hello World" example from SLF4J is not working for me. I guess this is because I added slf4j-log4 to my classpath. Should I configure log4j directly for the hello world to work?

log4j:WARN No appenders could be found for logger (HelloWorld).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

Update: I added log4j initialization, and it still doesn't work:

public static void main(String[] params) {
        org.apache.log4j.Logger.getRootLogger().addAppender(new ConsoleAppender());
        Logger logger = org.slf4j.LoggerFactory.getLogger(TestBase.class);
        logger.info("Hello World");
    }

And I'm getting:

log4j:ERROR No output stream or file set for the appender named [null].

@Michael, I admit that I more skimmed than read. I see that they ask me to add slf4j-simple.jar to my classpath, but I really do want to use log4j. Edited my question title accordingly. — ripper234, Nov 30 '10 at 06:15
@Stas - I'm still undecided. http://stackoverflow.com/questions/4311086/any-reason-for-a-new-project-to-use-log4j-instead-of-logback — ripper234, Nov 30 '10 at 06:22
When a console warning gives you a URL to look at, and the URL says `Knowing the appropriate location to place log4j.properties or log4j.xml requires understanding the search strategy of the class loader in use.`, it's generally advisable to spend a few minutes understanding the search strategy rather than jumping straight to stackoverflow for help. — Michael Kopinsky, Nov 30 '10 at 06:27

score 84 · Accepted Answer · answered Nov 30 '10 at 06:40

84

If you want to use slf4j simple, you need these jar files on your classpath:

slf4j-api-1.6.1.jar
slf4j-simple-1.6.1.jar

If you want to use slf4j and log4j, you need these jar files on your classpath:

slf4j-api-1.6.1.jar
slf4j-log4j12-1.6.1.jar
log4j-1.2.16.jar

No more, no less. Using slf4j simple, you'll get basic logging to your console at INFO level or higher. Using log4j, you must configure it accordingly.

answered Nov 30 '10 at 06:40

darioo

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i am using slf4j with log4j. I included all the three dependencies as mentioned but still it shows the same error. Please help me out. Thanks – user Feb 26 '14 at 21:27
For me log4j-1.2.16.jar is not required to make it work. – pmartin8 Jan 28 '20 at 15:07

ylu · Answer 2 · 2018-09-09T21:18:01.397

Following is an example. You can see the details http://jkssweetlife.com/configure-slf4j-working-various-logging-frameworks/ and download the full codes here.

Add following dependency to your pom if you are using maven, otherwise, just download the jar files and put on your classpath

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.7</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.7</version>
</dependency>

Configure log4j.properties

log4j.rootLogger=TRACE, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd'T'HH:mm:ss.SSS} %-5p [%c] - %m%n

Java example

public class Slf4jExample {
    public static void main(String[] args) {

        Logger logger = LoggerFactory.getLogger(Slf4jExample.class);

        final String message = "Hello logging!";
        logger.trace(message);
        logger.debug(message);
        logger.info(message);
        logger.warn(message);
        logger.error(message);
    }
}

@ylu, do you need to specify the scope for slf4j-log4j12 to be test? like here: https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12/1.7.25 — soMuchToLearnAndShare, Jul 20 '17 at 14:05
@MinnieShi if you ONLY want slf4j-log4j12 available for the test compilation and execution phases, then you can specify scope as test. If scope is not specified like what I did above, default scope is "compile"(meaning dependency is available for compile, runtime and test). Hope it helps. — ylu, Jul 22 '17 at 19:15

score 5 · Answer 3 · answered Feb 22 '16 at 06:59

you need to add 3 dependency ( API+ API implementation + log4j dependency) 
Add also this 
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.5</version>
</dependency>

# And to see log in command line , set log4j.properties 

# Root logger option
log4j.rootLogger=INFO, file, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

#And to see log in file  , set log4j.properties 
# Direct log messages to a log file
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./logs/logging.log
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=10
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

score 2 · Answer 4 · answered Aug 12 '20 at 09:24

Here a working example to use slf4j as façade with log4j in the backend:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>xxx</groupId>
    <artifactId>xxx</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.30</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.30</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.13.3</version>
        </dependency>
    </dependencies>
</project>

src/main/resources/log4j.properties

# Root logger option
log4j.rootLogger=DEBUG, stdout

# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

src/main/java/Main.java

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Main {
    private static final Logger logger = LoggerFactory.getLogger(Main.class);

    /**
     * Default private constructor.
     */
    private Main() {
    }

    /**
     * Main method.
     *
     * @param args Arguments passed to the execution of the application
     */
    public static void main(final String[] args) {
        logger.info("Message to log");
    }
}

score 0 · Answer 5 · answered Mar 02 '14 at 22:27

I had the same problem. I called my own custom logger in the log4j.properties file from code when using log4j api directly. If you are using the slf4j api calls, you are probably using the default root logger so you must configure that to be associated with an appender in the log4j.properties:


    # Set root logger level to DEBUG and its only appender to A1.
    log4j.rootLogger=DEBUG, A1

    # A1 is set to be a ConsoleAppender.
    log4j.appender.A1=org.apache.log4j.ConsoleAppender

How to get SLF4J "Hello World" working with log4j?

5 Answers5

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