背景：
今天新生成一个springboot项目，然而启动日志，还有mybatis的详细日志无法打印出来，自写程序中打印的日志可以输出；网上找了很多资料，都没法解决问题；于是决定跟一下源码，弄清springboot日志相关的逻辑。
环境配置：macbook； intellij idea community edition 2020.03 ； gradle 6.8.3 jdk1.8 ；
gradle引用包如下：
dependencies { compile "com.alibaba:fastjson:1.2.75" compile "mysql:mysql-connector-java" //spring compile("org.springframework.boot:spring-boot-starter") compile("org.mybatis.spring.boot:mybatis-spring-boot-starter:2.1.4") compile("org.springframework.boot:spring-boot-starter-web") compile("org.springframework.boot:spring-boot-starter-actuator") //lombok compileOnly 'org.projectlombok:lombok' annotationProcessor 'org.projectlombok:lombok' //test testCompile('org.springframework.boot:spring-boot-starter-test') testImplementation 'io.projectreactor:reactor-test'}
springboot 默认日志使用的是logback(引入spring-boot-starter包后，就自动引入了logback-core,logback-classic两个包，当然还有slf4j的包)，当springboot启动时，org.springframework.boot.context.logging.LoggingApplicationListener，该类211行注册的监控事件会被ApplicationStartingEvent触发；如下代码所示，会调用onApplicationStartingEvent初始化loggingSystem，而使用哪个日志组件，就要看loggingSystem初始化的值了
@Override public void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationStartingEvent) { onApplicationStartingEvent((ApplicationStartingEvent) event); } else if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event); } else if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent((ApplicationPreparedEvent) event); } else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event).getApplicationContext().getParent() == null) { onContextClosedEvent(); } else if (event instanceof ApplicationFailedEvent) { onApplicationFailedEvent(); } } private void onApplicationStartingEvent(ApplicationStartingEvent event) { this.loggingSystem = LoggingSystem.get(event.getSpringApplication().getClassLoader()); this.loggingSystem.beforeInitialize(); }
如下图是org.springframework.boot.logging.LoggingSystem类里面get函数的内容：首先会从system.getProperty中获取className，新生成的项目，取到的这个值都为空，SYSTEM_PROPERTY是一个固定值，就是该类的名字；那么loggingSystem的值就是从SYSTEM_FACTORY.getLoggingSystem(classLoader);获取到的；接下来我们得看LoggingSystemFactory.fromSpringFactories.getLoggingSystem取的值是什么了；
public static final String SYSTEM_PROPERTY = LoggingSystem.class.getName();private static final LoggingSystemFactory SYSTEM_FACTORY = LoggingSystemFactory.fromSpringFactories();public static LoggingSystem get(ClassLoader classLoader) { String loggingSystemClassName = System.getProperty(SYSTEM_PROPERTY); if (StringUtils.hasLength(loggingSystemClassName)) { if (NONE.equals(loggingSystemClassName)) { return new NoOpLoggingSystem(); } return get(classLoader, loggingSystemClassName); } LoggingSystem loggingSystem = SYSTEM_FACTORY.getLoggingSystem(classLoader); Assert.state(loggingSystem != null, "No suitable logging system located"); return loggingSystem; } private static LoggingSystem get(ClassLoader classLoader, String loggingSystemClassName) { try { Class<?> systemClass = ClassUtils.forName(loggingSystemClassName, classLoader); Constructor<?> constructor = systemClass.getDeclaredConstructor(ClassLoader.class); constructor.setAccessible(true); return (LoggingSystem) constructor.newInstance(classLoader); } catch (Exception ex) { throw new IllegalStateException(ex); } }
LoggingSystemFactory是一个接口，它的实现类在spring-boot-start有4个，其中3个是在内部内类实现，DelegatingLoggingSystemFactory（JavaLoggingSystem，Log4J2LoggingSystem，LogbackLoggingSystem，内部类实现）。上面SYSTEM_FACTORY的实现就是DelegatingLoggingSystemFactory这个类，如下代码中delegates的值为JavaLoggingSystem，Log4J2LoggingSystem，LogbackLoggingSystem；三个类具体的加载逻辑在SpringFactoriesLoader.loadFactories函数中，最终返回的loggingSystem就是前面函数返回列表中的第一个；SpringFactoriesLoader.loadFactories 才是决定springboot默认会使用哪个日志组件关键：该类是spring的核心组件类，在spring-core包中，org.springframework.core.io.support.SpringFactoriesLoader；loggingSystem的值=LogbackLoggingSystem
public interface LoggingSystemFactory { /** * Return a logging system implementation or {@code null} if no logging system is * available. * @param classLoader the class loader to use * @return a logging system */ LoggingSystem getLoggingSystem(ClassLoader classLoader); /** * Return a {@link LoggingSystemFactory} backed by {@code spring.factories}. * @return a {@link LoggingSystemFactory} instance */ static LoggingSystemFactory fromSpringFactories() { return new DelegatingLoggingSystemFactory( (classLoader) -> SpringFactoriesLoader.loadFactories(LoggingSystemFactory.class, classLoader)); } }class DelegatingLoggingSystemFactory implements LoggingSystemFactory { private final Function<ClassLoader, List<LoggingSystemFactory>> delegates; /** * Create a new {@link DelegatingLoggingSystemFactory} instance. * @param delegates a function that provides the delegates */ DelegatingLoggingSystemFactory(Function<ClassLoader, List<LoggingSystemFactory>> delegates) { this.delegates = delegates; } @Override public LoggingSystem getLoggingSystem(ClassLoader classLoader) { List<LoggingSystemFactory> delegates = (this.delegates != null) ? this.delegates.apply(classLoader) : null; if (delegates != null) { for (LoggingSystemFactory delegate : delegates) { LoggingSystem loggingSystem = delegate.getLoggingSystem(classLoader); if (loggingSystem != null) { return loggingSystem; } } } return null; } }
总结：虽然springboot会加载JavaLoggingSystem，Log4J2LoggingSystem，LogbackLoggingSystem三个日志实现类，但在选择时，还是会使用LogbackLoggingSystem作为它的日志框架
到此这篇关于springboot默认日志框架选择源码解析的文章就介绍到这了,更多相关springboot日志框架内容请搜索以前的文章或继续浏览下面的相关文章希望大家以后多多支持！
游手好闲会使人心智生锈
