SLF4J 簡介

SLF4J即 Simple Logging Facade for Java，是對各種log框架的抽象。

版本變化

1.6.0

如果沒有與特定的log框架綁定，則SLF4J默認爲一個無操作的實現。

1.7.0

logger接口中的打印方法提供了可變參數varargs（從JDK5開始支持），替代了Object[]。

即由

Object[] arguments = {
new Integer(7),
new Date(),
"a disturbance in the Force"
};

String result = MessageFormat.format(
"At {1,time} on {1,date}, there was {2} on planet "
+ "{0,number,integer}.", arguments);

簡化爲

String result = MessageFormat.format(
"At {1,time} on {1,date}, there was {2} on planet "
+ "{0,number,integer}.",
7, new Date(), "a disturbance in the Force");

1.7.5

Significant improvement in logger
retrieval times.

1.7.9

By
setting the

slf4j.detectLoggerNameMismatch

system property to true, SLF4J can automatically spot
incorrectly named loggers.

Hello World

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

public class HelloWorld {
public static void main(String[] args) {
Logger logger = LoggerFactory.getLogger(HelloWorld.class);
logger.info("Hello World");
}
}

只添加slf4j-api-1.7.13.jar會出現警告：

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.

因爲此時SLF4J還未綁定，最簡單的情況可以添加slf4j-simple-1.7.13.jar，得到正確輸出

0 [main] INFO HelloWorld - Hello World

Typical usage pattern

注意佔位符{}的使用

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

public class Wombat {

final Logger logger = LoggerFactory.getLogger(Wombat.class);
Integer t;
Integer oldT;

public void setTemperature(Integer temperature) {

oldT = t;
t = temperature;

logger.debug("Temperature set to {}. Old temperature was {}.", t, oldT);

if(temperature.intValue() > 50) {
logger.info("Temperature has risen above 50 degrees.");
}
}
}

綁定特定的log框架



logback-classic-1.0.13.jar (requires
logback-core-1.0.13.jar)

NATIVE IMPLEMENTATION There are also SLF4J bindings external to the SLF4J project, e.g. logback which implements SLF4J natively. Logback's ch.qos.logback.classic.Logger class is a direct implementation of SLF4J's org.slf4j.Logger interface. Thus, using SLF4J
in conjunction with logback involves strictly zero memory and computational overhead.

maven中的設置

<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.0.13</version>
</dependency>

兼容性

slf4j-api的所有版本都是互相兼容的（也就是說版本的變遷，不用改變code），需要考慮的只是綁定版本是否與slf4j-api兼容，如slf4j-api-1.7.13應該使用 slf4j-simple-1.7.13，使用slf4j-simple-1.5.5就會出現問題。

通過SLF4J統一logging

please refer to the page onBridging
legacy APIs.

MDC

目前只有log4j和logback支持MDC，如果使用不支持MDC的框架，SLF4J仍將存儲MDC數據，但用戶需要手動取回數據。

For
more information on MDC please see thechapter on
MDC in the logback manual.