我用log4j2运行了一个jetty webapp。它不记录任何内容，并且在启动时出现以下错误：
ERROR StatusLogger LogManager返回了org.apache.logging.slf4j.SLF4JLoggerContextFactory的示例，该示例未实现org.apache.logging.log4j.core.impl.Log4jContextFactory。无法初始化Log4j。

我的登录码：

org.apache.logging.log4j.Logger logger = org.apache.logging.log4j.LogManager.getLogger(MyClass.class);
logger.info("something");

log4j2.xml：

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
    <Properties>
        <property name="layout.pattern">%d %5p %c{1.} [%t] %m%n</property>
    </Properties>

    <Appenders>
        <Console name="consoleAppender">
            <PatternLayout pattern="${layout.pattern}" />
        </Console>

        <RollingFile name="rollingFileAppender">
            <FileName>logs/app.log</FileName>
            <FilePattern>logs/%d{yyyy-MM-dd}-app.log</FilePattern>
            <PatternLayout pattern="${layout.pattern}" />
            <Policies>
                <TimeBasedTriggeringPolicy />
                <SizeBasedTriggeringPolicy size="250 MB" />
            </Policies>
            <DefaultRolloverStrategy fileIndex="nomax" />
        </RollingFile>
    </Appenders>

    <Loggers>
        <Root level="info">
            <AppenderRef ref="consoleAppender" />
        </Root>
        <Logger name="com.app" level="all"
            additivity="false">
            <AppenderRef ref="consoleAppender" />
            <AppenderRef ref="rollingFileAppender" />
        </Logger>
    </Loggers>
</Configuration>

怎么了？