在jar文件中配置SLF4J

Question

I have my own jar file which is used as a library for my main application. I need to set SLF4J as my logger and configure it in my jar.

• Write logs into a file
• Set other configurations in a property file

When it is googled, there are samples for web apps. Any one let me know how to do above functionalities or mention any useful resource.

Answer 1

For a library, you should only include slf4j-api.jar . This means that in your code, you should only use classes within SLF4J's API, ie LoggerFactory and Logger .

Your library should not define anything else regarding logging. It's the responsibility of the application that uses your library to define the underlying logging implementation (logback, log4j, jcl, etc) and include the necessary bindings , as well as the underlying logging platform's configuration, such as a logback.xml file.

Please refer to the SLF4J manual for further reference.

Answer 2

To log something using slf4j, you must include the slf4j-api jar in your application. This is the bare minimum that is nessesary for slf4j logging. If using maven, it can be included in the pom as shown below

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.10</version>
</dependency>

However the default logging behavior in slf4j is very simple. In nearly all circumstances you will want to send slf4j logs to a logging framework, which can perform more complex logging. There are several jars that can be included to accomplish this. I use log4j, so the examples below are for that framework. In order to log over log4j, slf4j-log4j12 jar is needed.

Pom dependancy

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.10</version>
</dependency>

From there all slf4j logs will be redirected to log4j, which will work normally. Configure it through a log4j.properties file. The below example log4j.properties will log things both to the console, and to the /tmp/logfile.log file. remove the console appender to only log to the file.

# Root logger option
log4j.rootLogger=INFO, stdout, file

# Redirect log messages to console
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{ABSOLUTE} %5p %c{1}:%L - %m%n

# Redirect log messages to a log file, support file rolling.
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=/tmp/logfile.log
log4j.appender.file.MaxFileSize=5MB
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

If you want to log with a different framework, include the appropriate jar, and configure the underlying framework as you otherwise would.

Answer 3

SLF4J is not a logger, therefore you cannot configure anything. Use Logback.