让你的spring-boot应用日志随心所欲--spring boot日志深入分析
1.spring boot日志概述
spring boot使用Commons Logging作为内部的日志系统，并且给Java Util Logging，Log4J2以及Logback都提供了默认的配置。
如果使用了spring boot的Starters，那么默认会使用Logback用于记录日志。
2.spring boot日志默认配置
我们启动一个空的spring-boot项目看一下控制台的日志
控制台的默认配置
logging.pattern.console=%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}
其中%clr为配置不同的颜色输出，支持的颜色有以下几种：
blue
cyan
faint
green
magenta
red
yellow
输出顺序分析：
1、日期和时间--精确到毫秒，并按照时间进行简单的排序，格式为：
%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint}
2、日志级别--ERROR,WARN,INFO,DEBUG,TRACE
%clr(${LOG_LEVEL_PATTERN:-%5p})
3、进程ID号
%clr(${PID:- })
4、日志内容，用"---"分隔符分开
%clr(---){faint}
5、线程名字--括在方括号中
%clr([.15t]){faint}
6、日志的名字--通常对应的是类名
%clr(%-40.40logger{39}){cyan}
注意：Logback没有FATAL级别（映射到ERROR）
不同日志级别对应的颜色如下
3.spring boot日志配置
可以通过application.properties或者application.yml查看所有配置
每个配置后面都有说明，就不一一赘述了。
4.spring boot日志实现原理
点击配置属性，可以进入LoggingApplicationListener这个类，
`/**
- An {@link ApplicationListener} that configures the {@link LoggingSystem}. If the
- environment contains a {@code logging.config} property it will be used to bootstrap the
- logging system, otherwise a default configuration is used. Regardless, logging levels
- will be customized if the environment contains {@code logging.level.*} entries and
- logging groups can be defined with {@code logging.group}.
- Debug and trace logging for Spring, Tomcat, Jetty and Hibernate will be enabled when
- the environment contains {@code debug} or {@code trace} properties that aren't set to
- {@code "false"} (i.e. if you start your application using
- {@literal java -jar myapp.jar [--debug | --trace]}). If you prefer to ignore these
- properties you can set {@link #setParseArgs(boolean) parseArgs} to {@code false}.
- By default, log output is only written to the console. If a log file is required the
- {@code logging.path} and {@code logging.file} properties can be used.
- Some system properties may be set as side effects, and these can be useful if the
- logging configuration supports placeholders (i.e. log4j or logback):
- {@code LOG_FILE} is set to the value of path of the log file that should be written
- (if any).
- {@code PID} is set to the value of the current process ID if it can be determined.
*/`
它实现了GenericApplicationListener接口，它默认定义了日志组DEFAULT_GROUP_LOGGERS和日志级别LOG_LEVEL_LOGGERS
private static final Map> DEFAULT_GROUP_LOGGERS; static { MultiValueMap loggers = new LinkedMultiValueMap<>(); loggers.add("web", "org.springframework.core.codec"); loggers.add("web", "org.springframework.http"); loggers.add("web", "org.springframework.web"); loggers.add("web", "org.springframework.boot.actuate.endpoint.web"); loggers.add("web", "org.springframework.boot.web.servlet.ServletContextInitializerBeans"); loggers.add("sql", "org.springframework.jdbc.core"); loggers.add("sql", "org.hibernate.SQL"); DEFAULT_GROUP_LOGGERS = Collections.unmodifiableMap(loggers); } private static final Map> LOG_LEVEL_LOGGERS; static { MultiValueMap loggers = new LinkedMultiValueMap<>(); loggers.add(LogLevel.DEBUG, "sql"); loggers.add(LogLevel.DEBUG, "web"); loggers.add(LogLevel.DEBUG, "org.springframework.boot"); loggers.add(LogLevel.TRACE, "org.springframework"); loggers.add(LogLevel.TRACE, "org.apache.tomcat"); loggers.add(LogLevel.TRACE, "org.apache.catalina"); loggers.add(LogLevel.TRACE, "org.eclipse.jetty"); loggers.add(LogLevel.TRACE, "org.hibernate.tool.hbm2ddl"); LOG_LEVEL_LOGGERS = Collections.unmodifiableMap(loggers); } 你也可以自定义logging.level和logging.group,它们都是map结构。LoggingApplicationListener重写了onApplicationEvent方法，实现日志的打印
@Override public void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationStartingEvent) { onApplicationStartingEvent((ApplicationStartingEvent) event); //1 } else if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); //2 } else if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent((ApplicationPreparedEvent) event); //3 } else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event) .getApplicationContext().getParent() == null) { onContextClosedEvent(); //4 } else if (event instanceof ApplicationFailedEvent) { onApplicationFailedEvent(); //5 } }第一步：根据classloader里加载的依赖决定使用哪个日志系统？
主要实现有JavaLoggingSystem，Log4J2LoggingSystem，LogbackLoggingSystem
private void onApplicationStartingEvent(ApplicationStartingEvent event) { this.loggingSystem = LoggingSystem .get(event.getSpringApplication().getClassLoader()); this.loggingSystem.beforeInitialize(); }第二步：通过classpath，enviroment等获取参数初始化日志系统
/** * Initialize the logging system according to preferences expressed through the * {@link Environment} and the classpath. * @param environment the environment * @param classLoader the classloader */ protected void initialize(ConfigurableEnvironment environment, ClassLoader classLoader) { new LoggingSystemProperties(environment).apply(); LogFile logFile = LogFile.get(environment); if (logFile != null) { logFile.applyToSystemProperties(); } initializeEarlyLoggingLevel(environment); initializeSystem(environment, this.loggingSystem, logFile); initializeFinalLoggingLevels(environment, this.loggingSystem); registerShutdownHookIfNecessary(environment, this.loggingSystem); }第三步：注册springBootLoggingSystem
private void onApplicationPreparedEvent(ApplicationPreparedEvent event) { ConfigurableListableBeanFactory beanFactory = event.getApplicationContext() .getBeanFactory(); if (!beanFactory.containsBean(LOGGING_SYSTEM_BEAN_NAME)) { beanFactory.registerSingleton(LOGGING_SYSTEM_BEAN_NAME, this.loggingSystem); } }第四步和第五步：日志系统清洗
private void onContextClosedEvent() { if (this.loggingSystem != null) { this.loggingSystem.cleanUp(); } } private void onApplicationFailedEvent() { if (this.loggingSystem != null) { this.loggingSystem.cleanUp(); } }5.自定义配置文件
日志系统 自定义配置文件
Logback
logback-spring.xml, logback-spring.groovy, logback.xml, or logback.groovy
Log4j2
log4j2-spring.xml or log4j2.xml
JDK (Java Util Logging)
logging.properties
6.总结
spring boot日志系统封装了logback，log4j2和java log，默认情况下使用java log，一旦使用各种starts，则默认使用Log4J2，也可以通过classpath来改变，pom.xml指定
org.springframework.boot spring-boot-starter org.springframework.boot spring-boot-starter-logging org.springframework.boot spring-boot-starter-log4j 参考资料【1】https://docs.spring.io/spring-boot/docs/2.1.2.RELEASE/reference/htmlsingle/#boot-features-logging-format
【2】https://www.jb51.net/article/133795.htm