从源码分析 SpringBoot 的 LoggingSystem → 它是如何绑定日志组件的
开心一刻
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![成功给我逗笑了](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816145736631-60696630.gif)
前情回顾
SpringBoot2.7 霸王硬上弓 Logback1.3 → 不甜但解渴 实现了 spring-boot 2.x.x
与 logback 1.3.x
的集成,分两步
- 关闭 Spring Boot 的 LoggingSystem
- 配置文件用 logback.xml
从示例看,集成是成功的;但有些问题是没有分析的,比如
- System.setProperty("org.springframework.boot.logging.LoggingSystem", "none") 是如何生效的
- Spring Boot 的 LoggingSystem 是如何与日志组件绑定的
- Spring Boot 默认依赖 3 个日志组件:logback、log4j、jul,为什么默认启用的是 logback,而非其它两个?
基于如上 3 个问题,我们一起去翻一翻 Spring Boot 的源码;在看源码之前,我先带大家回顾一些内容,方便下文的源码分析
-
讲了观察者模式的实现,以及在 JDK 中的应用(JDK 事件模型)、Spring 中的应用(事件机制);大家可以重点看下 Spring 的那个案例,使用非常简单,总结一句就是
SpringBoot 启动过程中发送的事件,所有 ApplicationListener 都会收到(即 onApplicationEvent 方法会被调用)
-
spring-boot-2.0.3启动源码篇一 - SpringApplication构造方法
大家不要通篇去读,重点看
getSpringFactoriesInstances
,与本文息息相关的归纳成一句查找类路径下全部的 META-INF/spring.factories 的文件路径,并加载所有 spring.factories 中的内容到 SpringFactoriesLoader 的 cache 中,然后从缓存中获取 ApplicationListener 类型的类并进行实例化
下文是基于 Spring Boot 默认情况下的源码分析,而非集成 logback 1.3.x 的源码分析,大家注意下
集成 logback 1.3.x 需要关闭 Spring Boot 的 LoggingSystem,那还分析个毛
源码分析
问题来了,从哪开始跟?我就不绕圈子了,从 LoggingApplicationListener
开始跟,首先它在 META-INF/spring.factories
中
![spring.factories_LoggingApplicationListener](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816145815362-771143525.png)
其次它实现了 ApplicationListener
![LoggingApplicationListener类图](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816145834131-1151520536.png)
那么 Spring Boot 在启动过程中会实例化 LoggingApplicationListener
,Spring Boot 启动过程中发送的事件都会来到 LoggingApplicationListener
的 onApplicationEvent
方法
@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) {
onContextClosedEvent((ContextClosedEvent) event);
}
else if (event instanceof ApplicationFailedEvent) {
onApplicationFailedEvent();
}
}
Spring Boot 启动过程分不同的阶段,在每个阶段都会发送对应阶段的事件,LoggingApplicationListener
针对这些事件会有不同的处理,我们暂且只需要关注以下事件
ApplicationStartingEvent,对应的处理方法:onApplicationStartingEvent
ApplicationEnvironmentPreparedEvent,对应的处理方法:onApplicationEnvironmentPreparedEvent
ApplicationPreparedEvent,对应的处理方法:onApplicationPreparedEvent
onApplicationStartingEvent
private void onApplicationStartingEvent(ApplicationStartingEvent event) {
this.loggingSystem = LoggingSystem.get(event.getSpringApplication().getClassLoader());
this.loggingSystem.beforeInitialize();
}
方法很简单,获取日志系统,然后调用其 beforeInitialize
方法,我们跟进 LoggingSystem.get
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;
}
打个断点调试下,你们就会发现 SYSTEM_PROPERTY
的值是 org.springframework.boot.logging.LoggingSystem
![system_property](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816145856500-1147908749.png)
从系统属性中获取 org.springframework.boot.logging.LoggingSystem
,是不是和
System.setProperty("org.springframework.boot.logging.LoggingSystem", "none") 是如何生效的
对应上了?如果获取的值是 none
,直接返回 NoOpLoggingSystem
实例
/**
* {@link LoggingSystem} that does nothing.
*/
static class NoOpLoggingSystem extends LoggingSystem {
@Override
public void beforeInitialize() {
}
@Override
public void setLogLevel(String loggerName, LogLevel level) {
}
@Override
public List<LoggerConfiguration> getLoggerConfigurations() {
return Collections.emptyList();
}
@Override
public LoggerConfiguration getLoggerConfiguration(String loggerName) {
return null;
}
}
全是空实现,相当于关闭了 Spring Boot 的 LoggingSystem;org.springframework.boot.logging.LoggingSystem
还可以设置成其他值,但需要有对应的实现。默认情况下 loggingSystemClassName
的值是 null
,会跳过 if 来到 SYSTEM_FACTORY.getLoggingSystem(classLoader);
@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;
}
这里推荐用断点调试去跟源码,按 F7
之后会来到 LoggingSystemFactory#fromSpringFactories
/**
* 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));
}
SpringFactoriesLoader.loadFactories
是不是很眼熟?(不眼熟的去看:spring-boot-2.0.3启动源码篇一 - SpringApplication构造方法)此时它会做三件事
-
从 SpringFactoriesLoader#cache 中获取 LoggingSystemFactory 类型的工厂类的类名列表
之前已经加载到 SpringFactoriesLoader#cache 中,所以此时从缓存中获取;注意看三个实现类的顺序,
LogbackLoggingSystem.Factory
在最前面 -
实例化这些工厂类
-
对这些工厂类实例按 @Order 升序排序
这三个工厂类的 @Order 值是一样的,都是
@Order(Ordered.LOWEST_PRECEDENCE)
,所以顺序不变,LogbackLoggingSystem.Factory
仍在最前面
回到 DelegatingLoggingSystemFactory#getLoggingSystem
,对这些工厂类实例逐个遍历,得到 LoggingSystem
立即返回,不再遍历后面的工厂实例;第一个遍历的的是 LogbackLoggingSystem.Factory
,调用其 getLoggingSystem
方法
private static final boolean PRESENT = ClassUtils.isPresent("ch.qos.logback.classic.LoggerContext",
Factory.class.getClassLoader());
@Override
public LoggingSystem getLoggingSystem(ClassLoader classLoader) {
if (PRESENT) {
return new LogbackLoggingSystem(classLoader);
}
return null;
}
ch.qos.logback.classic.LoggerContext
存在(即存在logback依赖),直接创建 LogbackLoggingSystem
实例并返回;至此 Spring Boot 的 LoggingSystem 确定将基于 logback
,而非 log4j
,也非 jul
,问题
Spring Boot 的 LoggingSystem 是如何与日志组件绑定的
Spring Boot 默认依赖 3 个日志组件:logback、log4j、jul,为什么默认启用的是 logback,而非其它两个?
是不是清楚了?LoggingSystem 确定为 LogbackLoggingSystem 后回到 LoggingApplicationListener#onApplicationStartingEvent
方法的第二行,即调用 LogbackLoggingSystem#beforeInitialize
方法
@Override
public void beforeInitialize() {
LoggerContext loggerContext = getLoggerContext();
if (isAlreadyInitialized(loggerContext)) {
return;
}
super.beforeInitialize();
loggerContext.getTurboFilterList().add(FILTER);
}
主要初始化 LoggerContext
,跟进 getLoggerContext()
private LoggerContext getLoggerContext() {
ILoggerFactory factory = StaticLoggerBinder.getSingleton().getLoggerFactory();
Assert.isInstanceOf(LoggerContext.class, factory,
() -> String.format(
"LoggerFactory is not a Logback LoggerContext but Logback is on "
+ "the classpath. Either remove Logback or the competing "
+ "implementation (%s loaded from %s). If you are using "
+ "WebLogic you will need to add 'org.slf4j' to "
+ "prefer-application-packages in WEB-INF/weblogic.xml",
factory.getClass(), getLocation(factory)));
return (LoggerContext) factory;
}
StaticLoggerBinder
有没有很熟悉?看下它的全类名:org.slf4j.impl.StaticLoggerBinder
,在 logback-classic-1.2.12.jar
下 ,而 logback 1.3.x
没有这个类
所以 spring-boot 2.x.x 默认不支持 logback 1.3.x
总结下,onApplicationStartingEvent
方法确定了日志系统是 LogbackLoggingSystem
onApplicationEnvironmentPreparedEvent
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
SpringApplication springApplication = event.getSpringApplication();
if (this.loggingSystem == null) {
this.loggingSystem = LoggingSystem.get(springApplication.getClassLoader());
}
initialize(event.getEnvironment(), springApplication.getClassLoader());
}
很显然 loggingSystem
不为 null
,我们直接跟 initialize
方法
protected void initialize(ConfigurableEnvironment environment, ClassLoader classLoader) {
getLoggingSystemProperties(environment).apply();
this.logFile = LogFile.get(environment);
if (this.logFile != null) {
this.logFile.applyToSystemProperties();
}
// 日志分组,暂不关注
this.loggerGroups = new LoggerGroups(DEFAULT_GROUP_LOGGERS);
// 设置早期日志级别,主要debug和trace之间的抉择
initializeEarlyLoggingLevel(environment);
// 初始化日志系统
initializeSystem(environment, this.loggingSystem, this.logFile);
// 设置最终日志级别
initializeFinalLoggingLevels(environment, this.loggingSystem);
registerShutdownHookIfNecessary(environment, this.loggingSystem);
}
我们暂时只关注 initializeSystem
方法
![initializeSystempng](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150021444-1374231757.png)
继续往下跟,来到 LogbackLoggingSystem#initialize
![LogbackLoggingSystem](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150041137-789171987.png)
继续往下跟,来到 AbstractLoggingSystem#initialize
![AbstractLoggingSystem](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150058873-1606493342.png)
继续往下跟,来到 AbstractLoggingSystem#initializeWithConventions
private void initializeWithConventions(LoggingInitializationContext initializationContext, LogFile logFile) {
String config = getSelfInitializationConfig();
if (config != null && logFile == null) {
// self initialization has occurred, reinitialize in case of property changes
reinitialize(initializationContext);
return;
}
if (config == null) {
config = getSpringInitializationConfig();
}
if (config != null) {
loadConfiguration(initializationContext, config, logFile);
return;
}
loadDefaults(initializationContext, logFile);
}
其中 getSelfInitializationConfig()
就是从 classpath
下逐个寻找
logback-test.groovy, logback-test.xml, logback.groovy, logback.xml
这四个文件,一旦找到则直接返回;因为找到了 logback.xml
,所以来到第一个 if
![initializeWithConventions-reinitialize](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150122882-429196684.png)
继续跟进,来到 LogbackLoggingSystem#reinitialize
![LogbackLoggingSystem](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150152060-1971396875.png)
将logback.xml
中的配置进行加载;至此,Spring Boot 的 LoggingSystem 与 Logback 的绑定就完成了,你们清楚了吗?
我们重新回到 AbstractLoggingSystem#initializeWithConventions
,如果 classpath
下
logback-test.groovy, logback-test.xml, logback.groovy, logback.xml
这四个文件都没有,会来到 config = getSpringInitializationConfig();
,逐步跟下去会来到 AbstractLoggingSystem#getSpringConfigLocations
protected String[] getSpringConfigLocations() {
String[] locations = getStandardConfigLocations();
for (int i = 0; i < locations.length; i++) {
String extension = StringUtils.getFilenameExtension(locations[i]);
locations[i] = locations[i].substring(0, locations[i].length() - extension.length() - 1) + "-spring."
+ extension;
}
return locations;
}
这个方法大家都能看懂吧,locations
的值
logback-test.groovy, logback-test.xml, logback.groovy, logback.xml
逐个遍历,然后进行拼接,最终得到
logback-test-spring.groovy, logback-test-spring.xml, logback-spring.groovy, logback-spring.xml
![getSpringConfigLocations](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150240602-96019077.png)
同样从 classpath
下逐个寻找,一旦找到直接返回;这也是为什么我们的日志配置文件是 logback-spring.xml
也能生效的原因。我们可以给 Spring Boot 的日志配置文件排个优先级
logback-test.groovy > logback-test.xml > logback.groovy > logback.xml > logback-test-spring.groovy > logback-test-spring.xml > logback-spring.groovy > logback-spring.xml
总结下,onApplicationEnvironmentPreparedEvent
完成了日志系统的初始化(日志配置文件的加载)
onApplicationPreparedEvent
private void onApplicationPreparedEvent(ApplicationPreparedEvent event) {
ConfigurableApplicationContext applicationContext = event.getApplicationContext();
ConfigurableListableBeanFactory beanFactory = applicationContext.getBeanFactory();
if (!beanFactory.containsBean(LOGGING_SYSTEM_BEAN_NAME)) {
beanFactory.registerSingleton(LOGGING_SYSTEM_BEAN_NAME, this.loggingSystem);
}
if (this.logFile != null && !beanFactory.containsBean(LOG_FILE_BEAN_NAME)) {
beanFactory.registerSingleton(LOG_FILE_BEAN_NAME, this.logFile);
}
if (this.loggerGroups != null && !beanFactory.containsBean(LOGGER_GROUPS_BEAN_NAME)) {
beanFactory.registerSingleton(LOGGER_GROUPS_BEAN_NAME, this.loggerGroups);
}
if (!beanFactory.containsBean(LOGGING_LIFECYCLE_BEAN_NAME) && applicationContext.getParent() == null) {
beanFactory.registerSingleton(LOGGING_LIFECYCLE_BEAN_NAME, new Lifecycle());
}
}
代码不复杂,就是注册了几个 Bean
到 Spring 容器,其中的 loggingSystem
是我们暂时比较关注的,默认情况下其类型是:LogbackLoggingSystem
日志打印
Spring Boot 的 LoggingSystem 完成与 Logback 的绑定后,它是如何使用然后打印日志的呢?是不是也像
![业务日志打印样例](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150303650-937804483.png)
这样来使用的?那绝对不可能的!
![绝对不可能](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150318332-1614212628.gif)
这么使用的话,跟 Spring Boot 的 LoggingSystem 有鸡毛的关系?我们来看下 Spring Boot 中日志的使用,SpringApplication
179 行就用到了
![SpringApplicaton179行](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150334270-1075629947.png)
我们会发现 Log
、LogFactory
在 spring-jcl-5.3.31.jar
包下
![spring-jcl_LogFactory](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150412816-1658308872.png)
spring-jcl 类似 slf4j,也是一个日志门面,本文不展开
跟进 LogFactory.getLog
,一路跟下去会来到 LogAdapter#createLog
public static Log createLog(String name) {
switch (logApi) {
case LOG4J:
return Log4jAdapter.createLog(name);
case SLF4J_LAL:
return Slf4jAdapter.createLocationAwareLog(name);
case SLF4J:
return Slf4jAdapter.createLog(name);
default:
// Defensively use lazy-initializing adapter class here as well since the
// java.logging module is not present by default on JDK 9. We are requiring
// its presence if neither Log4j nor SLF4J is available; however, in the
// case of Log4j or SLF4J, we are trying to prevent early initialization
// of the JavaUtilLog adapter - e.g. by a JVM in debug mode - when eagerly
// trying to parse the bytecode for all the cases of this switch clause.
return JavaUtilAdapter.createLog(name);
}
}
logApi
的值获取如下
private static final String LOG4J_SPI = "org.apache.logging.log4j.spi.ExtendedLogger";
private static final String LOG4J_SLF4J_PROVIDER = "org.apache.logging.slf4j.SLF4JProvider";
private static final String SLF4J_SPI = "org.slf4j.spi.LocationAwareLogger";
private static final String SLF4J_API = "org.slf4j.Logger";
private static final LogApi logApi;
static {
if (isPresent(LOG4J_SPI)) {
if (isPresent(LOG4J_SLF4J_PROVIDER) && isPresent(SLF4J_SPI)) {
// log4j-to-slf4j bridge -> we'll rather go with the SLF4J SPI;
// however, we still prefer Log4j over the plain SLF4J API since
// the latter does not have location awareness support.
logApi = LogApi.SLF4J_LAL;
}
else {
// Use Log4j 2.x directly, including location awareness support
logApi = LogApi.LOG4J;
}
}
else if (isPresent(SLF4J_SPI)) {
// Full SLF4J SPI including location awareness support
logApi = LogApi.SLF4J_LAL;
}
else if (isPresent(SLF4J_API)) {
// Minimal SLF4J API without location awareness support
logApi = LogApi.SLF4J;
}
else {
// java.util.logging as default
logApi = LogApi.JUL;
}
}
根据优先级逐个去类路径下寻找类,找到了直接返回;Spring Boot 默认情况下用的是 SLF4J + Logback,所以 logApi
的值是 SLF4J_SPI
,那么 LogAdapter#createLog
的返回值的类型是 LogAdapter$Slf4jLocationAwareLog
![LogAdapter$Slf4jLocationAwareLog](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150433106-913576500.png)
相当于完成了 spring-jcl
到 slf4j
的适配;这么说来,Spring Boot 日志还是走的 SLF4J + Logback ?跟 Spring Boot 的 LoggingSystem 有什么关系呢?敬请期待下篇
![未完待续](https://img2024.cnblogs.com/blog/747662/202408/747662-20240816150449253-862119648.jpg)
总结
-
onApplicationStartingEvent
确定日志系统类型并创建对应的
LoggingSystem
,默认情况下是LogbackLoggingSystem
-
onApplicationEnvironmentPreparedEvent
完成日志配置文件的加载以及
LoggingSystem
的初始化 -
Spring Boot 的日志打印貌似与 LoggingSystem 没有关系?下篇分析