一直使用log4j，虽然知道log4j有性能上的问题，logback和log4j2都已经流行很多年了，但是总是懒得升级。最近新项目使用了spring boot，默认是配置logback，刚好学习一下。
logback的配置很像log4j，而且起核心概念也是跟log4j一样。不外乎就是logger，appender和layout的关系，只不过appender多了一个filter组件。具体可以参考我前面写过的文章: log4j详细介绍。
下面看具体实际问题的解决方案。
1. 多套环境（dev, test, idc）logback配置问题
logback的加载顺序如下 Chapter 3: Logback configuration :
Let us begin by discussing the initialization steps that logback follows to try to configure itself:
Logback tries to find a file called logback.groovy in the classpath.
If no such file is found, logback tries to find a file called logback-test.xml in the classpath.
If no such file is found, it checks for the file logback.xml in the classpath.
If no such file is found, service-provider loading facility (introduced in JDK 1.6) is used to resolve the implementation of com.qos.logback.classic.spi.Configurator interface by looking up the file META-INF\services\ch.qos.logback.classic.spi.Configurator in the class path. Its contents should specify the fully qualified class name of the desired Configurator implementation.
If none of the above succeeds, logback configures itself automatically using the BasicConfigurator which will cause logging output to be directed to the console.
The last step is meant as last-ditch effort to provide a default (but very basic) logging functionality in the absence of a configuration file.
上面的介绍没有介绍指定路径的方式。但是实际上logback跟log4j一样，是支持指定配置文件路径的。Specifying the location of the default configuration file as a system property
Specifying the location of the default configuration file as a system property
You may specify the location of the default configuration file with a system property named “logback.configurationFile”. The value of this property can be a URL, a resource on the class path or a path to a file external to the application.
java -Dlogback.configurationFile=/path/to/config.xml chapters.configuration.MyApp1
Note that the file extension must be “.xml” or “.groovy”. Other extensions are ignored. Explicitly registering a status listener may help debugging issues locating the configuration file.
所以我们可以简单的通过一个环境变量来支持多套环境，就像spring boot的application-{profile}.properties配置文件一样。 创建logback-{spring.profiles.active}.xml配置文件，然后启动的时候指定 -Dspring.profiles.active=production，达到动态切换的目的。
除了这种方式，我们还可以利用logback的条件配置达到不同环境不同配置的效果。
<if condition='"prd".equals(property("environment")) || "stg".equals(property("environment"))'>
<then>
<property name="APPLINK_LOG_LEVEL" value="warn"/>
</then>
<else>
<property name="APPLINK_LOG_LEVEL" value="debug"/>
</else>
</if>
还可以利用文件导入，做一个间接转发 Logging with logback and external configuration:
<?xml version="1.0" encoding="UTF-8"?>
<configuration scan="true" scanPeriod="300 seconds">
<property resource="logback.properties" />
<if condition='property("env").equals("prod")'>
<then>
<include file="logback-prod.xml" />
</then>
</if>
<if condition='property("env").equals("dev")'>
<then>
<include resource="logback-dev.xml" />
</then>
</if>
</configuration>
Logback对log4j的功能增强
logback多log4j最大的贡献是解决了性能问题。不过在功能性方面，也做了很多改进：
- 自动扫描变化
- appender filter
- 支持基本的条件配置
- 支持文件导入(file inclusion)
- 支持格式化日志，logger.error(“one two three: {} {} {}”, “a”, “b”, “c”, new Exception(“something went wrong”));
TIPS logback配置模板参考
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
<layout class="ch.qos.logback.classic.PatternLayout">
<pattern>%date [%thread] %highlight(%-5level) %logger{26} - %msg%n</pattern>
</layout>
</appender>
<appender name="SYSTEM"
class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${LOG_DIR}/system.log</file>
<encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
<pattern>%date [%thread] %highlight(%-5level) %logger{26} - %msg%n</pattern>
</encoder>
<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
<!-- rollover daily -->
<fileNamePattern>${LOG_DIR}/archived/system.%d{yyyy-MM-dd}.log
</fileNamePattern>
<!-- keep 30 days' worth of history -->
<maxHistory>30</maxHistory>
<timeBasedFileNamingAndTriggeringPolicy
class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
<maxFileSize>100MB</maxFileSize>
</timeBasedFileNamingAndTriggeringPolicy>
</rollingPolicy>
</appender>
<appender name="APP"
class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${LOG_DIR}/app.log</file>
<encoder class="ch.qos.logback.classic.encoder.PatternLayoutEncoder">
<pattern>%date [%thread] %highlight(%-5level) %logger{26} - %msg%n</pattern>
</encoder>
<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
<!-- rollover daily -->
<fileNamePattern>${LOG_DIR}/archived/app.%d{yyyy-MM-dd}.log
</fileNamePattern>
<!-- keep 30 days' worth of history -->
<maxHistory>30</maxHistory>
<timeBasedFileNamingAndTriggeringPolicy
class="ch.qos.logback.core.rolling.SizeAndTimeBasedFNATP">
<maxFileSize>100MB</maxFileSize>
</timeBasedFileNamingAndTriggeringPolicy>
</rollingPolicy>
</appender>
<appender name="REMOTE"
class="me.arganzheng.study.toolkit.logging.client.appender.logback.AsyncSocketAppender">
<remoteHost>10.242.77.38</remoteHost>
<port>4560</port>
<application>api-gateway-web</application>
<!-- <threadPoolSize>2</threadPoolSize> <loadBalancerName>WRR</loadBalancerName> -->
<filter class="ch.qos.logback.classic.filter.ThresholdFilter">
<level>ERROR</level>
</filter>
</appender>
<logger name="me.arganzheng.study.mobopay.applications.api.gateway" level="debug"
additivity="false">
<appender-ref ref="APP" />
<appender-ref ref="REMOTE" />
</logger>
<root level="info">
<appender-ref ref="CONSOLE" />
<appender-ref ref="SYSTEM" />
<appender-ref ref="REMOTE" />
</root>
</configuration>
