spring boot 配置logback，logback不打印日志

spring boot 日志简介

spring boot只依赖 Commons Logging API，而不依赖其他日志（jul、logback、log4j）。要想使用logback，必须引入jcl-over-slf4j( 实现了 Commons Logging API)，将jcl转接到slf4j。所有的spring boot starter都依赖了spring-boot-starter-logging，pom如下

<dependencies>
		<dependency>
			<groupId>ch.qos.logback</groupId>
			<artifactId>logback-classic</artifactId>
		</dependency>
		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-to-slf4j</artifactId>
		</dependency>
		<dependency>
			<groupId>org.slf4j</groupId>
			<artifactId>jul-to-slf4j</artifactId>
		</dependency>
	</dependencies>

可以看到spring-boot-starter-logging引入了logback，同时将log4j、jul都转接到slf4j，这就是为什么引入jcl-over-slf4j就能使logback生效的原因。
如想修改日志级别，在application.properties中设置logging.level即可。

logging.level.org.springframework.web=DEBUG
logging.level.org.hibernate=ERROR

通过logging.file修改日志文件位置。

spring boot 配置logback

类路径下新建logback.xml或者logback-spring.xml，推荐使用后者，因为它能利用spring boot既有logback配置。xml与properties方式相比，能更细粒度的控制。

spring boot提供了logback的默认配置org/springframework/boot/logging/logback/base.xml

<included>
	<include resource="org/springframework/boot/logging/logback/defaults.xml" />
	<property name="LOG_FILE" value="${LOG_FILE:-${LOG_PATH:-${LOG_TEMP:-${java.io.tmpdir:-/tmp}}}/spring.log}"/>
	<include resource="org/springframework/boot/logging/logback/console-appender.xml" />
	<include resource="org/springframework/boot/logging/logback/file-appender.xml" />
	<root level="INFO">
		<appender-ref ref="CONSOLE" />
		<appender-ref ref="FILE" />
	</root>
</included>

它引入了defaults.xml、console-appender.xml、file-appender.xml

---

defaults.xml配置了tomcat、hibernate的日志级别，规定了控制台及文件的输出格式。

<included>
	<conversionRule conversionWord="clr" converterClass="org.springframework.boot.logging.logback.ColorConverter" />
	<conversionRule conversionWord="wex" converterClass="org.springframework.boot.logging.logback.WhitespaceThrowableProxyConverter" />
	<conversionRule conversionWord="wEx" converterClass="org.springframework.boot.logging.logback.ExtendedWhitespaceThrowableProxyConverter" />
	<property name="CONSOLE_LOG_PATTERN" value="${CONSOLE_LOG_PATTERN:-%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}"/>
	<property name="FILE_LOG_PATTERN" value="${FILE_LOG_PATTERN:-%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}} ${LOG_LEVEL_PATTERN:-%5p} ${PID:- } --- [%t] %-40.40logger{39} : %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}}"/>

	<logger name="org.apache.catalina.startup.DigesterFactory" level="ERROR"/>
	<logger name="org.apache.catalina.util.LifecycleBase" level="ERROR"/>
	<logger name="org.apache.coyote.http11.Http11NioProtocol" level="WARN"/>
	<logger name="org.apache.sshd.common.util.SecurityUtils" level="WARN"/>
	<logger name="org.apache.tomcat.util.net.NioSelectorPool" level="WARN"/>
	<logger name="org.eclipse.jetty.util.component.AbstractLifeCycle" level="ERROR"/>
	<logger name="org.hibernate.validator.internal.util.Version" level="WARN"/>
</included>

---

console-appender.xml使用了defaults.xml规定的控制台输出格式。

<included>
	<appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
		<encoder>
			<pattern>${CONSOLE_LOG_PATTERN}</pattern>
		</encoder>
	</appender>
</included>

---

file-appender.xml使用了defaults.xml规定的文件输出格式，并会按照大小和时间分片，文件最大10M。

<included>
	<appender name="FILE"
		class="ch.qos.logback.core.rolling.RollingFileAppender">
		<encoder>
			<pattern>${FILE_LOG_PATTERN}</pattern>
		</encoder>
		<file>${LOG_FILE}</file>
		<rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
			<fileNamePattern>${LOG_FILE}.%d{yyyy-MM-dd}.%i.gz</fileNamePattern>
			<maxFileSize>${LOG_FILE_MAX_SIZE:-10MB}</maxFileSize>
			<maxHistory>${LOG_FILE_MAX_HISTORY:-0}</maxHistory>
		</rollingPolicy>
	</appender>
</included>

配置logback只输出到文件

新建logback-spring.xml 引入 file-appender.xml，没有引入 console-appender.xml，所以不会输出到控制台。

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <include resource="org/springframework/boot/logging/logback/defaults.xml" />
    <property name="LOG_FILE" value="${LOG_FILE:-${LOG_PATH:-${LOG_TEMP:-${java.io.tmpdir:-/tmp}}/}spring.log}"/>
    <include resource="org/springframework/boot/logging/logback/file-appender.xml" />
    <root level="INFO">
        <appender-ref ref="FILE" />
    </root>
</configuration>

总结

spring boot使用logback

• 引入jcl-over-slf4j
• 如果只改变日志级别，在application.properties中配置logging.level即可
• 细粒度的控制，新建logback-spring.xml，酌情引入defaults.xml、console-appender.xml、file-appender.xml

logback不起作用，使用了其他日志

在实践中，往往遇到logback不起作用的情况，通过mvn dependency:tree 查看依赖，一般来说都是因为引入了其它日志实现（log4j、apache commons log）导致，控制台一般会有提示，这种情况，排除掉其他日志实现 即可。比如

 <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>
                <exclusion>
                    <artifactId>log4j</artifactId>
                    <groupId>log4j</groupId>
                </exclusion>
            </exclusions>
        </dependency>

参考

spring boot howto-logging