lanboys / LogDemo

LogDemo

• logback节点配置详解
• logback的使用和logback.xml详解
• logback 配置详解
• java 日志框架总结
• log4j-over-slf4j与slf4j-log4j12共存stack overflow异常分析
• Java之常用日志框架
• JAVA日志框架概述
• slf4j与log4j、log4j2
• Spring Boot（十）Logback和Log4j2集成与日志发展史

LoggingApplicationListener.java

/**
 * 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}.
 **/

AbstractLoggingSystem.java

	@Override
	public void initialize(LoggingInitializationContext initializationContext, String configLocation, LogFile logFile) {
        // 如果配置了自定义 logging.config, 则使用自定义的配置文件，否则走默认流程
		if (StringUtils.hasLength(configLocation)) {
			initializeWithSpecificConfig(initializationContext, configLocation, logFile);
			return;
		}
		initializeWithConventions(initializationContext, logFile);
	}

	private void initializeWithSpecificConfig(LoggingInitializationContext initializationContext, String configLocation,
			LogFile logFile) {
		configLocation = SystemPropertyUtils.resolvePlaceholders(configLocation);
		loadConfiguration(initializationContext, configLocation, logFile);
	}

	private void initializeWithConventions(LoggingInitializationContext initializationContext, LogFile logFile) {
        // 获取日志本身支持的配置文件名
		String config = getSelfInitializationConfig();
        
		if (config != null && logFile == null) {
			// self initialization has occurred, reinitialize in case of property changes
            // 再次初始化
			reinitialize(initializationContext);
			return;
		}
        // 获取 *-spring.xml配置文件
		if (config == null) {
			config = getSpringInitializationConfig();
		}
		if (config != null) {
			loadConfiguration(initializationContext, config, logFile);
			return;
		}
		loadDefaults(initializationContext, logFile);

        // 优先级: 自定义 logging.config  > 框架本身支持的文件  > *-spring.xml  > springboot.jar 中提供的默认配置文件
        // 配置文件中的 属性 主要就是针对默认配置

        jar:file:/repository/org/springframework/boot/spring-boot/2.2.6.RELEASE/spring-boot-2.2.6.RELEASE.jar!
                 /org/springframework/boot/logging/log4j2/log4j2-file.xml
	}

Appender 里面拦截器分析

    UnsynchronizedAppenderBase.java

    public void doAppend(E eventObject) {
            .....
            // 返回 deny 则不打印
            if (getFilterChainDecision(eventObject) == FilterReply.DENY) {
                return;
            }

            // ok, we now invoke derived class' implementation of append
            this.append(eventObject);
            .....
    }

    FilterAttachableImpl.java

    /**
     * Loop through the filters in the list. As soon as a filter decides on
     * ACCEPT or DENY, then that value is returned. If all of the filters return
     * NEUTRAL, then NEUTRAL is returned.
     */
    public FilterReply getFilterChainDecision(E event) {

        final Filter<E>[] filterArrray = filterList.asTypedArray();
        final int len = filterArrray.length;

        for (int i = 0; i < len; i++) {
            final FilterReply r = filterArrray[i].decide(event);
            if (r == FilterReply.DENY || r == FilterReply.ACCEPT) {
                return r;
            }
        }

        // no decision
        return FilterReply.NEUTRAL;
    }

只要有拦截器返回 ACCEPT or DENY，就立马返回，不继续走拦截链了，类似于或的关系，所以特别注意不要在同一个拦截器中同时定义 ACCEPT or DENY，否则后面的拦截器就失效了，除非放最后面，或者有特殊需求