如何使用slf4j读取.properties文件？

Question

I am trying to make a simple program which reads the properties file and logs the output to console but I am not able to do that.

This is my class:

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

public final class Slf4jSample {

    public static void main(final String[] args) {
        final Logger logger = LoggerFactory.getLogger(Slf4jSample.class);

        logger.info("Hello World!");
    }

    private Slf4jSample() {
    }
}

And this is my properties file:

log4j.appender.A1=org.apache.log4j.ConsoleAppender
log4j.appender.A1.layout=org.apache.log4j.PatternLayout

log4j.logger.Slf4jSample=INFO, A1

When I run this it gives this exception:

log4j:WARN No appenders could be found for logger (com.slf4j.Slf4jSample).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

Answer 1

The "log4j:WARN No appenders could be found..." message indicates that SLF4J was correctly bound with log4j but log4j could not load your log4j.properties file. SLF4J is not the issue here. Just place log4j.properties on your classpath.

Answer 2

Considering that you are using slf4j with log4j as the underlying logging library, and you have both slf4j-log4j.jar and log4j.jar on your classpath, you then need to specify the location of the log4j.properites file.

Ceki mentioned to put log4j.properties on your classpath and it should pick it up automatically. If this is not working for you (it should), or you need the log4j.properties to exist outside the classpath, then you can add -Dlog4j.configuration=log4j.properties to your JVM arguments when executing your code. The value of this variable can be a full path, or is relative to the current directory where you are executing from.

For example, when exectuing JUnit tests in my IDE I commonly add this as a JVM argument in my Run Profile to ensure it picks up my properties file that is not inside my Java Project (ie not on classpath)

-Dlog4j.configuration=file:/C:/java/workspace/logs/log4j.properties