slf4j logback log4j的关系

一般getLogger有两种：

1）slf4j的LoggerFactory.getLogger

2) log4j的Logger.getLogger

第一种默认是用logback和logback.xml，如果没有logback的包，他也可以去找log4j。

第二种就是默认用log4j的了。

至于怎么配置slf4j来使用不同的实现，看
https://dzone.com/articles/how-configure-slf4j-different

Using 

slf4j

 with Simple logger

Create a Maven based project and this in your 

pom.xml

.

<dependency>

<groupId>org.slf4j</groupId>

<artifactId>slf4j-api</artifactId>

<version>1.7.5</version>

</dependency>

Now you may use 

Logger

 in your Java code like this.

package deng;

import org.slf4j.*;

public class Hello {

static Logger LOGGER = LoggerFactory.getLogger(Hello.class);

public static void main(String[] args) {

for (int i = 0; i < 10; i++)

if (i % 2 == 0)

LOGGER.info("Hello {}", i);

else

LOGGER.debug("I am on index {}", i);

}

}

The above will get your program compiled, but when you run it, you will see these output.

bash> java deng.Hello

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.

What it’s saying is that at runtime, you are missing the logging "implementation" (or the logger binding), so 

slf4j

simply
use a "NOP" implmentation, which does nothing. In order to see the output properly, you may try use ansimple implementation that does not require any configuration at all! Just go back to your 

pom.xml

 and
add the following:

<dependency>

<groupId>org.slf4j</groupId>

<artifactId>slf4j-simple</artifactId>

<version>1.7.5</version>

</dependency>

Now you see logging output on STDOUT with INFO level. This simple logger will default show any INFO level message or higher. In order to see DEBUG messages, you would need to pass in this System
Property 

-Dorg.slf4j.simpleLogger.defaultLogLevel=DEBUG

 at your Java startup.

Using 

slf4j

 with Log4j logger

Now we can experiment and swap different logger implementations, but your application code can remain the same. All we need is ot replace 

slf4j-simple

 with
another popular logger implementation, such as the Log4j.

<dependency>

<groupId>org.slf4j</groupId>

<artifactId>slf4j-log4j12</artifactId>

<version>1.7.5</version>

</dependency>

Again, we must configure logging per implementation that we picked. In this case, we need an

src/main/resources/log4j.properties

 file.

log4j.rootLogger=DEBUG, STDOUT

log4j.logger.deng=INFO

log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender

log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout

log4j.appender.STDOUT.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n

Re-run your program, and you should see similar output.

Using 

slf4j

 with JDK logger

The JDK actually comes with a logger package, and you can replace 

pom.xml

 with this logger implementation.

<dependency>

<groupId>org.slf4j</groupId>

<artifactId>slf4j-jdk14</artifactId>

<version>1.7.5</version>

</dependency>

Now the configuration for JDK logging is a bit difficult to work with. Not only need a config file, such as

src/main/resources/logging.properties

,
but you would also need to add a System properties 

-Djava.util.logging.config.file=logging.properties

 in order to have it pick it up. Here is an example to
get you started:

level=INFO

handlers=java.util.logging.ConsoleHandler

java.util.logging.ConsoleHandler.level=FINEST

deng.level=FINEST

Using 

slf4j

 with Logback logger

The logback logger implementation is a super dupa quality implementation. If you intend to write serious code that go into production, you may want to evaluate this option. Again modify your 

pom.xml

 to
replace with this:

<dependency>

<groupId>ch.qos.logback</groupId>

<artifactId>logback-classic</artifactId>

<version>1.0.13</version>

</dependency>

Here is a sample of configuration 

src/main/resources/logback.xml

 to get things started.

<configuration>

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">

<encoder>

<pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>

</encoder>

</appender>

<logger name="deng" level="DEBUG"/>

<root level="INFO">

<appender-ref ref="STDOUT" />

</root>

</configuration>