不思进取太久了，想捣鼓点新东西，刚好在log4j这一块有解决不了的问题，想换log4j2试试；以前也没有写过yaml，就想着顺便试试新的配置。

笔者使用maven构建Demo, 按官网Configuration with YAML的说明加入依赖

<dependency><groupId>com.fasterxml.jackson.dataformat</groupId><artifactId>jackson-dataformat-yaml</artifactId><version>2.8.6</version>
</dependency>

兴致勃勃写了个最简单的main方法，打印info级别的日志，跑起来却一直报：

ERROR StatusLogger No log4j2 configuration file found. Using default configuration: logging only errors to the console.

找不到log4j2的配置文件，笔者检查了几遍，配置文件明明已经编译成功，怎么会找不到呢？
网上找了很多相关的文章，都没发现有出现过类似的问题。。。

不能卡在这是吧，太想试试log4j2了, Debug源代码吧，这一Debug，我勒个去啊，jackson-dataformat-yaml这个依赖包还有些依赖没被引入，com.fasterxml.jackson.databind.ObjectMapper 在源文件里就就是红的...

导致YamlConfigurationFactory中的构造方法无法正常加载com.fasterxml.jackson.databind.ObjectMapper的Class...

private static final String[] dependencies = new String[] {"com.fasterxml.jackson.databind.ObjectMapper","com.fasterxml.jackson.databind.JsonNode","com.fasterxml.jackson.core.JsonParser","com.fasterxml.jackson.dataformat.yaml.YAMLFactory"
};private final boolean isActive;public YamlConfigurationFactory() {for (final String dependency : dependencies) {if (!Loader.isClassAvailable(dependency)) {LOGGER.debug("Missing dependencies for Yaml support");isActive = false;return;}}isActive = true;
}

isActive的结果为false, YamlConfigurationFactory的getConfiguration()获取配置永远为null

@Override
public Configuration getConfiguration(final LoggerContext loggerContext, final ConfigurationSource source) {if (!isActive) {return null;}return new YamlConfiguration(loggerContext, source);
}

解决方法：

加入jackson-databind依赖包

<dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.8.6</version>
</dependency>