SpringBoot日志管理

历史

1. 日志实现框架: JUL Logback Log4j Log4j2
2. 日志门面框架(抽象层): JCL slf4j, 避免代码改动影响用户使用

• JDK1.3前, 日志靠System.out/err.print, 存在巨大缺陷, 粒度不够细
• log4j出现, 于15年8月停止更新
• JDK1.4引入java.util.logging, JUL
• commons-logging出现, 解决日志实现框架的兼容问题
• log4j作者推出门面框架slf4j
• log4j作者推出logback

• log4j2对log4j重大升级, 修复bug, 极大提升性能

• 最佳组合: slf4j+logback, slf4j+log4j2

日志门面如何定位到日志实现

1. LoggerFactory.getLogger
2. findPossibleStaticLoggerBinderPathSet
3. 获取StaticLoggerBinder所在Jar路径
4. 如果存在多个日志实现就打印提示
5. 使用StaticLoggerBinder获取工程再实现 ```java public static Logger getLogger(String name) { ILoggerFactory iLoggerFactory = getILoggerFactory(); return iLoggerFactory.getLogger(name); }

public static ILoggerFactory getILoggerFactory() { //未初始化 if (INITIALIZATION_STATE == UNINITIALIZED) { synchronized (LoggerFactory.class) { if (INITIALIZATION_STATE == UNINITIALIZED) { //on初始化 INITIALIZATION_STATE = ONGOING_INITIALIZATION; //实现寻址 performInitialization(); } } } switch (INITIALIZATION_STATE) { case SUCCESSFUL_INITIALIZATION: return StaticLoggerBinder.getSingleton().getLoggerFactory(); case NOP_FALLBACK_INITIALIZATION: return NOP_FALLBACK_FACTORY; case FAILED_INITIALIZATION: throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG); case ONGOING_INITIALIZATION: // support re-entrant behavior. // See also http://jira.qos.ch/browse/SLF4J-97 return SUBST_FACTORY; } throw new IllegalStateException(“Unreachable code”); }

private final static void performInitialization() {
    bind();
    if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
        versionSanityCheck();
    }
}

private final static void bind() {
    try {
        Set<URL> staticLoggerBinderPathSet = null;
        // skip check under android, see also
        // http://jira.qos.ch/browse/SLF4J-328
        if (!isAndroid()) {
			//找到可能的LoggerBinder
            staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
			//判断当前集合Size, 如果大于1就打印输出提示
            reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
        }
        // the next line does the binding
		//获得Factory并获取对象
        StaticLoggerBinder.getSingleton();
		//启动状态未成功
        INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
		//打印出最终使用的日志框架
        reportActualBinding(staticLoggerBinderPathSet);
        fixSubstituteLoggers();
        replayEvents();
        // release all resources in SUBST_FACTORY
        SUBST_FACTORY.clear();
    } catch (NoClassDefFoundError ncde) {
        String msg = ncde.getMessage();
        if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
            INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
            Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
            Util.report("Defaulting to no-operation (NOP) logger implementation");
            Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
        } else {
            failedBinding(ncde);
            throw ncde;
        }
    } catch (java.lang.NoSuchMethodError nsme) {
        String msg = nsme.getMessage();
        if (msg != null && msg.contains("org.slf4j.impl.StaticLoggerBinder.getSingleton()")) {
            INITIALIZATION_STATE = FAILED_INITIALIZATION;
            Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
            Util.report("Your binding is version 1.5.5 or earlier.");
            Util.report("Upgrade your binding to version 1.6.x.");
        }
        throw nsme;
    } catch (Exception e) {
        failedBinding(e);
        throw new IllegalStateException("Unexpected initialization failure", e);
    }
}


static Set<URL> findPossibleStaticLoggerBinderPathSet() {
    // use Set instead of list in order to deal with bug #138
    // LinkedHashSet appropriate here because it preserves insertion order
    // during iteration
    Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
    try {
        ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
        Enumeration<URL> paths;
        if (loggerFactoryClassLoader == null) {
            paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
        } else {
            paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
        }
		//多路径的话就添加多次
        while (paths.hasMoreElements()) {
            URL path = paths.nextElement();
            staticLoggerBinderPathSet.add(path);
        }
    } catch (IOException ioe) {
        Util.report("Error getting resources from path", ioe);
    }
    return staticLoggerBinderPathSet;
} ```

日志使用

logger.debug(“xyz {} is {}”, i,j) 其他用法可以参考网上的配置.