Springboot加載日志子產品順序

Springboot加載日志子產品

Spring jcl

Spring jcl 是Springboot連接配接SLF4J的基礎包，實作了對Log4j 2.x API是否存在，以及Spring架構類路徑中的SLF4J 1.7api。

ServiceLoader

通過配置尋找接口的實作類，實作類的jar包的META-INF下建立一個檔案夾services，并在services下建立一個檔案，以接口的全限定名為檔案名，内容為實作類的全限定名。

參考連結：

https://www.jianshu.com/p/7601ba434ff4 https://blog.csdn.net/shi2huang/article/details/80308531

Log4j擷取ConfigurationFactory

核心代碼

String ALL_TYPES = "*";
for (final ConfigurationFactory factory : getFactories()) {
    final String[] types = factory.getSupportedTypes();
    if (types != null) {
        for (final String type : types) {
            // 隻有 XmlConfigurationFactory 符合條件
            if (type.equals(ALL_TYPES)) {
                final Configuration config = factory.getConfiguration(loggerContext, name, configLocation);
                if (config != null) {
                    return config;
                }
            }
        }
    }
}
           

Springboot加載log4j2的流程

Springboot 加載log4j2主要分為兩個階段，第一階段成為start， 第二階段為initalize

start階段

• LogAdapter利用Class.forName加載不同日志的實作，使用内部類進行調用
• log4j 通過PluginProcess對 @Plugin注釋識别ConfigurationFactory，具體可參考

  Springboot配置log4j2爬坑

initalize階段

初始化階段，SpringApplication.run()方法的 SpringApplicationRunListeners

• beforeInitialize()， 判斷是否以slf4j橋接。

if (isBridgeJulIntoSlf4j()) {
    removeJdkLoggingBridgeHandler();
    SLF4JBridgeHandler.install();
}

// ClassUtils.isPresent() Sping 實作的類似Class.forName功能
ClassUtils.isPresent(BRIDGE_HANDLER, getClassLoader());

           

• LoggingApplicationListener 代碼配置onApplicationEvent

public void onApplicationEvent(ApplicationEvent event) {
    // beforeInitalize 階段
    if (event instanceof ApplicationStartingEvent) {
        onApplicationStartingEvent((ApplicationStartingEvent) event);
    }
    // 環境配置，即initalizeing階段
    else if (event instanceof ApplicationEnvironmentPreparedEvent) {
        onApplicationEnvironmentPreparedEvent(
                (ApplicationEnvironmentPreparedEvent) event);
    }
    // 程式運作起來後，調用日志階段
    else if (event instanceof ApplicationPreparedEvent) {
        onApplicationPreparedEvent((ApplicationPreparedEvent) event);
    }
    
    // 程式關閉
    else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event)
            .getApplicationContext().getParent() == null) {
        onContextClosedEvent();
    }
    
    // 失敗
    else if (event instanceof ApplicationFailedEvent) {
        onApplicationFailedEvent();
    }
}
           

• Log4j2判斷日志是否為同一執行個體，利用了identityHashCoder給AppClassLoader做身份哈希判重
• shutdownhook 學習(有時間在研究)

private void registerShutdownHookIfNecessary(Environment environment,
        LoggingSystem loggingSystem) {
    boolean registerShutdownHook = environment
            .getProperty(REGISTER_SHUTDOWN_HOOK_PROPERTY, Boolean.class, false);
    if (registerShutdownHook) {
        Runnable shutdownHandler = loggingSystem.getShutdownHandler();
        if (shutdownHandler != null
                && shutdownHookRegistered.compareAndSet(false, true)) {
            registerShutdownHook(new Thread(shutdownHandler));
        }
    }
}

void registerShutdownHook(Thread shutdownHook) {
    Runtime.getRuntime().addShutdownHook(shutdownHook);
}