1.spring boot日志概述

spring boot使用Commons Logging作為內部的日志系統，并且給Java Util Logging，Log4J2以及Logback都提供了默認的配置。
如果使用了spring boot的Starters，那么默認會使用Logback用于記錄日志。

2.spring boot日志默認配置

我們啟動一個空的spring-boot項目看一下控制臺的日志

控制臺的默認配置

logging.pattern.console=%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}

其中%clr為配置不同的顏色輸出，支持的顏色有以下幾種：

• blue
• cyan
• faint
• green
• magenta
• red
• yellow

輸出順序分析：

1、日期和時間--精確到毫秒，并按照時間進行簡單的排序，格式為：

%clr(%d{${LOG_DATEFORMAT_PATTERN:-yyyy-MM-dd HH:mm:ss.SSS}}){faint}

2、日志級別--ERROR,WARN,INFO,DEBUG,TRACE

%clr(${LOG_LEVEL_PATTERN:-%5p})

3、進程ID號

%clr(${PID:- })

4、日志內容，用"---"分隔符分開

%clr(---){faint}

5、線程名字--括在方括號中

　　

%clr([%15.15t]){faint}

6、日志的名字--通常對應的是類名

　　

%clr(%-40.40logger{39}){cyan}

注意：Logback沒有FATAL級別（映射到ERROR）

不同日志級別對應的顏色如下

3.spring boot日志配置

可以通過application.properties或者application.yml查看所有配置

每個配置后面都有說明，就不一一贅述了。

4.spring boot日志實現原理

?點擊配置屬性，可以進入LoggingApplicationListener這個類，

/*** 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}.* <p>* 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}.* <p>* 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.* <p>* 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):* <ul>* <li>{@code LOG_FILE} is set to the value of path of the log file that should be written* (if any).</li>* <li>{@code PID} is set to the value of the current process ID if it can be determined.* </li>* </ul>** @author Dave Syer* @author Phillip Webb* @author Andy Wilkinson* @author Madhura Bhave* @since 2.0.0* @see LoggingSystem#get(ClassLoader)*/

它實現了GenericApplicationListener接口，它默認定義了日志組DEFAULT_GROUP_LOGGERS和日志級別LOG_LEVEL_LOGGERS

private static final Map<String, List<String>> DEFAULT_GROUP_LOGGERS;static {MultiValueMap<String, String> 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<LogLevel, List<String>> LOG_LEVEL_LOGGERS;static {MultiValueMap<LogLevel, String> 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);}

你也可以自定義logging.level和logging.group,它們都是map結構。LoggingApplicationListener重寫了onApplicationEvent方法，實現日志的打印

@Overridepublic 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：根據classloader里加載的依賴決定使用哪個日志系統？

主要實現有JavaLoggingSystem，Log4J2LoggingSystem，LogbackLoggingSystem

private void onApplicationStartingEvent(ApplicationStartingEvent event) {this.loggingSystem = LoggingSystem.get(event.getSpringApplication().getClassLoader());this.loggingSystem.beforeInitialize();}

第二步：通過classpath，enviroment等獲取參數初始化日志系統

/*** 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：注冊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：日志系統清洗

private void onContextClosedEvent() {if (this.loggingSystem != null) {this.loggingSystem.cleanUp();}}private void onApplicationFailedEvent() {if (this.loggingSystem != null) {this.loggingSystem.cleanUp();}}

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5.自定義配置文件

日志系統自定義配置文件

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

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6.總結

　　spring boot日志系統封裝了logback，log4j2和java log，默認情況下使用java log，一旦使用各種starts，則默認使用Log4J2，也可以通過classpath來改變，pom.xml指定

<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> <exclusions> <exclusion> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-logging</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-log4j</artifactId> </dependency>

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參考資料

【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

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轉載于:https://www.cnblogs.com/davidwang456/p/10997038.html

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