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

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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([%15.15t]){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，

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/** * 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

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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

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 @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

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   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

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/**     * 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

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    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

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    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

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<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>