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参考文档

http://logback.qos.ch/manual/configuration.html#conditional

Conditional processing is supported anywhere within the <configuration> element

maven

<dependency>
	<groupId>org.codehaus.janino</groupId>
	<artifactId>janino</artifactId>
	<version>${janino.version}</version>
</dependency>

if-then

<!-- if-then form -->
<if condition="some conditional expression">
<then>
  ...
</then>
</if>

if-then-else

<!-- if-then-else form -->
<if condition="some conditional expression">
<then>
  ...
</then>
<else>
  ...
</else>    
</if>

<if condition='property("HOSTNAME").contains("torino")'>
<then>
  <appender name="CON" class="ch.qos.logback.core.ConsoleAppender">
	<encoder>
	  <pattern>%d %-5level %logger{35} - %msg %n</pattern>
	</encoder>
  </appender>
  <root>
	<appender-ref ref="CON" />
  </root>
</then>
</if>

 嵌套

<if condition='p("log.dir.type").equals("custom")'>
	<then>
		<property scope="context" name="log.root.dir" value="${log.dir.custom}"/>
	</then>
	<else>
		<if condition='p("log.dir.type").equals("install")'>
			<then>
				<property scope="context" name="log.root.dir" value="${LOG_DIR}/logs"/>
			</then>
			<else>
				<if condition='p("os.name").contains("Windows")'>
					<then>
						<property scope="context" name="log.root.dir" value="c:/logs/"/>
					</then>
					<else>
						<property scope="context" name="log.root.dir" value="/tmp/logs"/>
					</else>
				</if>
			</else>
		</if>
	</else>
</if>

property()  或 p() 

the property() or its shorter equivalent p() 

isDefined()

判断key是否定义

The isDefined() method can be used to check whether a property is defined.

For example, to check whether the property “k” is defined you would write isDefined("k")

<if condition='isDefined("logging.mydir")'>
	<then>
		<property scope="context" name="LOG_FILE_DIR" value="${logging.mydir}"/>
	</then>
	<else>
		<property scope="context" name="LOG_FILE_DIR" value="c:/logs/otherdir"/>
	</else>

</if>

isNull

 if you need to check whether a property is null, the isNull() method is provided.

Example: isNull("k").