概述
默认情况下，springboot内部使用logback作为系统日志实现的框架，将日志输出到控制台，不会写到日志文件。如果在application.properties或application.yml配置，这样只能配置简单的场景，保存路径、日志格式等。复杂的场景（区分 info 和 error 的日志、每天产生一个日志文件等）满足不了，只能自定义配置文件logback-spring.xml或者logback.xml。
logback配置详解
首先我们先了解下logback。
logback 主要分为三个模块：
logback-core：是其他两个模块的基础模块
logback-classic：是对 core 模块的扩展，相当于 log4j 的改良版。classic 模块实现了 Slf4j 的 API 因此可以便于和其他日志框架直接切换
logback-access：与Servlet容器集成，以提供http访问日志功能。
logback配置
1.application .properties
# 日志打印信息配置
logging.config=classpath:logback-spring.xml
2.logback-spring.xml
logback %d{HH:mm:ss.SSS} %contextName [%thread] %-5level %logger{36} - %msg%n ./logs/gf_scanning.log ./logs/gf_scanning.%d{yyyy-MM-dd}.%i.log 30 10MB %d{HH:mm:ss.SSS} %contextName [%thread] %-5level %logger{36} - %msg%n
异常情况
遇到个奇怪的问题，按上述配置完成logback的配置后，大多项目可以正常运行并保存日志到文件，但有一个项目启动时报错。java.lang.IllegalStateException: Could not initialize Logback logging from classpath:logback-spring.xml ... Caused by: ch.qos.logback.core.joran.spi.JoranException: Parser configuration error occurred
Logging system failed to initialize using configuration from 'classpath:logback-spring.xml'
java.lang.IllegalStateException: Could not initialize Logback logging from classpath:logback-spring.xml
at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:168)
at org.springframework.boot.logging.AbstractLoggingSystem.initializeWithSpecificConfig(AbstractLoggingSystem.java:66)
at org.springframework.boot.logging.AbstractLoggingSystem.initialize(AbstractLoggingSystem.java:57)
at org.springframework.boot.logging.logback.LogbackLoggingSystem.initialize(LogbackLoggingSystem.java:132)
at org.springframework.boot.context.logging.LoggingApplicationListener.initializeSystem(LoggingApplicationListener.java:316)
at org.springframework.boot.context.logging.LoggingApplicationListener.initialize(LoggingApplicationListener.java:282)
at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEnvironmentPreparedEvent(LoggingApplicationListener.java:240)
at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:216)
at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:176)
at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:169)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:143)
at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:131)
at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:85)
at org.springframework.boot.SpringApplicationRunListeners.lambda$environmentPrepared$2(SpringApplicationRunListeners.java:66)
at java.util.ArrayList.forEach(ArrayList.java:1257)
at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:120)
at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:114)
at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:65)
at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:339)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:297)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301)
at cn.piesat.ScanningApplication.main(ScanningApplication.java:18)
Caused by: ch.qos.logback.core.joran.spi.JoranException: Parser configuration error occurred
at ch.qos.logback.core.joran.event.SaxEventRecorder.buildSaxParser(SaxEventRecorder.java:89)
at ch.qos.logback.core.joran.event.SaxEventRecorder.recordEvents(SaxEventRecorder.java:57)
at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:151)
at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:110)
at ch.qos.logback.core.joran.GenericConfigurator.doConfigure(GenericConfigurator.java:53)
at org.springframework.boot.logging.logback.LogbackLoggingSystem.configureByResourceUrl(LogbackLoggingSystem.java:188)
at org.springframework.boot.logging.logback.LogbackLoggingSystem.loadConfiguration(LogbackLoggingSystem.java:165)
... 22 more
Caused by: org.xml.sax.SAXNotSupportedException: Feature: http://xml.org/sax/features/external-general-entities
at org.apache.crimson.parser.XMLReaderImpl.setFeature(XMLReaderImpl.java:211)
at org.apache.crimson.jaxp.SAXParserImpl.setFeatures(SAXParserImpl.java:143)
at org.apache.crimson.jaxp.SAXParserImpl.(SAXParserImpl.java:126)
at org.apache.crimson.jaxp.SAXParserFactoryImpl.newSAXParserImpl(SAXParserFactoryImpl.java:113)
at org.apache.crimson.jaxp.SAXParserFactoryImpl.setFeature(SAXParserFactoryImpl.java:141)
at ch.qos.logback.core.joran.event.SaxEventRecorder.buildSaxParser(SaxEventRecorder.java:82)
... 28 more
Disconnected from the target VM, address: '127.0.0.1:64222', transport: 'socket'Process finished with exit code 1
可能是由于jar包冲突，在pom文件中单独引入logback-core的依赖后，问题解决。
ch.qos.logback logback-core 1.1.7 ch.qos.logback logback-classic 1.1.7 ch.qos.logback logback-core
