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配置文件的优先级

1. 优先找classPath下的logback-test.xml文件。
2. 如果找不到，再找classPath下的logback.groovy文件。
3. 如果找不到，再找classPath下的logback.xml 文件。
4. 如果找不到，再找SPI机制下
   
com.qos.logback.classic.spi.Configurator

   接口的实现类。
5. 如果没有SPI机制下
   
com.qos.logback.classic.spi.Configurator

   接口的实现类，使用logback中的默认实现类
   
BasicConfigurator

   。它将日志内容输出到控制台上。

这里再额外说明下，如果你使用

java -Dlogback.configurationFile=/path/to/config.xml chapters.configuration.MyApp1

这种

方式启动

，则可以使用你想要的任意配置文件创建logContext，这在帮助你学习logback时是非常有用的。

configuration的debug属性

<configuration debug="true"> 

  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> 
    <!-- encoders are  by default assigned the type
         ch.qos.logback.classic.encoder.PatternLayoutEncoder -->
    <encoder>
      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
  </appender>

  <root level="debug">
    <appender-ref ref="STDOUT" />
  </root>
</configuration>

debug属性，会使应用启动时在控制台上打印出 context上下文的加载处置情况。等效于代码

StatusPrinter.print(logContext)

, 也等效于配置文件中配置

statusListener

标签，如下

<configuration>
  <statusListener class="ch.qos.logback.core.status.OnConsoleStatusListener" />  

  ... the rest of the configuration file  
</configuration>

当然，

logback.debug

系统属性生效优先级高于配置文件debug属性，但是这是基于存在配置文件的前提下的, 参考一下

logback历史上一个修复的issue

。我们看看logback内部加载行为状态是什么样的。

21:28:23,474 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback-test.xml]
21:28:23,474 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Could NOT find resource [logback.groovy]
21:28:23,475 |-INFO in ch.qos.logback.classic.LoggerContext[default] - Found resource [logback.xml] at [file:/Users/ruchen/IdeaProjects/java-framework/java-logback/target/classes/logback.xml]
21:28:23,547 |-INFO in ch.qos.logback.core.joran.action.ImplicitModelAction - Assuming default class name [ch.qos.logback.classic.encoder.PatternLayoutEncoder] for tag [encoder]
21:28:23,548 |-INFO in ch.qos.logback.core.joran.action.ImplicitModelAction - Assuming default class name [ch.qos.logback.classic.encoder.PatternLayoutEncoder] for tag [encoder]
21:28:23,548 |-INFO in ch.qos.logback.core.joran.action.ImplicitModelAction - Assuming default class name [ch.qos.logback.classic.encoder.PatternLayoutEncoder] for tag [encoder]
21:28:23,625 |-INFO in ch.qos.logback.classic.model.processor.LoggerModelHandler@17ed40e0 - Setting level of logger [CONSOLE_LOGGER] to DEBUG
21:28:23,625 |-INFO in ch.qos.logback.classic.model.processor.LoggerModelHandler@50675690 - Setting level of logger [CONSOLE_LOGGER1] to DEBUG
21:28:23,625 |-INFO in ch.qos.logback.classic.model.processor.RootLoggerModelHandler@31b7dea0 - Setting level of ROOT logger to DEBUG
21:28:23,626 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@47d384ee - Processing appender named [ROOT]
21:28:23,626 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@47d384ee - About to instantiate appender of type [ch.qos.logback.core.rolling.RollingFileAppender]
21:28:23,649 |-INFO in c.q.l.core.rolling.TimeBasedRollingPolicy@1784662007 - No compression will be used
21:28:23,651 |-INFO in c.q.l.core.rolling.TimeBasedRollingPolicy@1784662007 - Will use the pattern logback.log.%d{yyyy-MM-dd} for the active file
21:28:23,654 |-INFO in c.q.l.core.rolling.DefaultTimeBasedFileNamingAndTriggeringPolicy - The date pattern is 'yyyy-MM-dd' from file name pattern 'logback.log.%d{yyyy-MM-dd}'.
21:28:23,654 |-INFO in c.q.l.core.rolling.DefaultTimeBasedFileNamingAndTriggeringPolicy - Roll-over at midnight.
21:28:23,656 |-INFO in c.q.l.core.rolling.DefaultTimeBasedFileNamingAndTriggeringPolicy - Setting initial period to Sat Dec 05 21:18:32 CST 2020
21:28:23,669 |-INFO in ch.qos.logback.core.rolling.RollingFileAppender[ROOT] - Active log file name: logback.log
21:28:23,669 |-INFO in ch.qos.logback.core.rolling.RollingFileAppender[ROOT] - File property is set to [logback.log]
21:28:23,669 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@47d384ee - Attaching appender [ROOT] to Logger[ROOT]
21:28:23,670 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@13c78c0b - Processing appender named [CONSOLE]
21:28:23,670 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@13c78c0b - About to instantiate appender of type [ch.qos.logback.core.ConsoleAppender]
21:28:23,672 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@13c78c0b - Attaching appender [CONSOLE] to Logger[CONSOLE_LOGGER]
21:28:23,672 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@337d0578 - Processing appender named [CONSOLE1]
21:28:23,672 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@337d0578 - About to instantiate appender of type [ch.qos.logback.core.ConsoleAppender]
21:28:23,672 |-INFO in ch.qos.logback.core.model.processor.AppenderModelHandler@337d0578 - Attaching appender [CONSOLE1] to Logger[CONSOLE_LOGGER1]
21:28:23,675 |-INFO in ch.qos.logback.core.model.processor.DefaultProcessor@6276ae34 - End of configuration.
21:28:23,675 |-INFO in ch.qos.logback.classic.joran.JoranConfigurator@5cc7c2a6 - Registering current configuration as safe fallback point

configuration的scan属性

logback配置文件一旦发生变化，logback支持重新加载文件，这是基于logback框架中一个后台

线程

实现的。默认情况下，logback一分钟加载一次，你可以改写，比如通过下面的方式

<configuration scan="true" scanPeriod="30 seconds" > 
</configuration> 

appender累积规则

level继承规则

logger的additivity属性

<configuration>

  <appender name="FILE" class="ch.qos.logback.core.FileAppender">
    <file>foo.log</file>
    <encoder>
      <pattern>%date %level [%thread] %logger{10} [%file : %line] %msg%n</pattern>
    </encoder>
  </appender>

  <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%msg%n</pattern>
    </encoder>
  </appender>

  <logger name="chapters.configuration.Foo" additivity="false">
    <appender-ref ref="FILE" />
  </logger>

  <root level="debug">
    <appender-ref ref="STDOUT" />
  </root>
</configuration>

默认情况下，logger的

additivity

属性为true。就图中这个配置文件，如果不配置该属性为false，会导致 name声明为

chapters.configuration.Foo

的logger在输出日志时 控制台 和 文件各输出一份，因为logger存在继承行为。

当该属性为false时，直接阻断了logger中appender的累加行为(cumulative behaviour)，声明 name声明为

chapters.configuration.Foo

的logger不再输出到console，只有文件。

变量替代&作用域

变量替代比较常见，不再赘述。作用域提一下，scope主要有

local

,

context

,

system

。

优先级 local > context > system， 也就是说优先取local中的变量值，找不到才找context，最后找system。