使用log4j2,控制台可以正常输出日志,但是log4j2日志文件为空?

红太狼 2022-05-31 06:20 698阅读 0赞

Log4j-2-does-not-write-to-file.md

问题: 使用log4j2, 控制台可以正常输出日志，但是log4j2日志文件为空？

配置文件log4j2.xml配置如下:

<?xml version="1.0" encoding="UTF-8"?>
    <Configuration>  
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </Console>
            <File name="MyTestLog" fileName="MyTestLog.txt" immediateFlush="false" append="true">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </File>
        </Appenders>
        <Loggers>
            <Logger name="org.apache.log4j.xml" level="debug">
                <AppenderRef ref="MyTestLog"/>
            </Logger>
            <Root level="error">
                <AppenderRef ref="Console" level="error"/>
            </Root>
        </Loggers>
    </Configuration>

Java文件名为`Log4jDemo.java`, 代码如下:

// Log4jDemo.java
    import org.apache.logging.log4j.*;
    
    public class Log4jDemo {
        static Logger logger = LogManager.getLogger(Log4jDemo.class.getName());
        public static void main(String[] args) {
            System.out.println("=> Hello Log4jDemo...");
            logger.trace("trace level");
            logger.debug("debug level");
            logger.info("info level");
            logger.warn("warn level");
            logger.error("error level");
            logger.fatal("fatal level");
        }
    }

网上搜了好多资料都没能看明白，只看看到这段文字:

> It is not writing to your file because the Logger you are using to log is named log4j2Demo.LogDemo but the logger you have configured is named “a.demo.of.log4j2”.  
> Since the names don’t match it will use the root logger, which you have configured to log to the console.

## 解决办法1: ##

重新修改配置文件,将Loggers中Logger的name改成”Log4jDemo”, 与java类文件同名:

<?xml version="1.0" encoding="UTF-8"?>
    <Configuration>  
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </Console>
            <File name="MyTestLog" fileName="MyTestLog.txt" immediateFlush="false" append="true">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </File>
        </Appenders>
        <Loggers>
            <Logger name="Log4jDemo" level="debug">
                <AppenderRef ref="MyTestLog"/>
            </Logger>
            <Root level="all">
                <AppenderRef ref="Console" level="error"/>
            </Root>
        </Loggers>
    </Configuration>

## 解决办法2: ##

Loggers里Root下配置两个AppenderRef，一个指向Console，一个指向MyTestLog:

<?xml version="1.0" encoding="UTF-8"?>
    <Configuration>  
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </Console>
            <File name="MyTestLog" fileName="MyTestLog.txt" immediateFlush="false" append="true">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </File>
        </Appenders>
        <Loggers>
            <Root level="all">
                <AppenderRef ref="Console" level="error"/>
                <AppenderRef ref="MyTestLog" level="info" />
            </Root>
        </Loggers>
    </Configuration>

控制台输出:

=> Hello Log4jDemo...
    18-01-24 15:57:09.547 [main] ERROR Log4jDemo - error level
    18-01-24 15:57:09.547 [main] FATAL Log4jDemo - fatal level

查看日志文件，已经有内容了:

$ tail MyTestLog.txt
    18-01-24 15:57:09.544 [main] INFO  Log4jDemo - info level
    18-01-24 15:57:09.547 [main] WARN  Log4jDemo - warn level
    18-01-24 15:57:09.547 [main] ERROR Log4jDemo - error level
    18-01-24 15:57:09.547 [main] FATAL Log4jDemo - fatal level

注意到，控制台和日志文件中的内容并不一样，这是因为我们配置的日志级别不同，Console配置的是`error`, MyTestLog配置的是`info`。

## 解决办法3: AsyncAppender with Console and File ##

<?xml version="1.0" encoding="UTF-8"?>
    <Configuration>  
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </Console>
            <File name="MyTestLog" fileName="MyTestLog.txt" immediateFlush="false" append="true">
                <PatternLayout pattern="%d{yy-MM-dd HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n" />
            </File>
            <Async name="ASYNC">
                <AppenderRef ref="MyTestLog"/>
                <AppenderRef ref="Console"/>
                </Async>
        </Appenders>
        <Loggers>
            <Root level="all">
                <AppenderRef ref="ASYNC"/>
            </Root>
        </Loggers>
    </Configuration>

## 参考链接 ##

[https://logging.apache.org/log4j/2.x/manual/migration.html][https_logging.apache.org_log4j_2.x_manual_migration.html]  
[https://codedump.io/share/UwYEUh9AtRfg/1/log4j2-output-not-written-to-log-file][https_codedump.io_share_UwYEUh9AtRfg_1_log4j2-output-not-written-to-log-file]  
[https://stackoverflow.com/questions/25118993/log4j-2-doesnt-write-to-file][https_stackoverflow.com_questions_25118993_log4j-2-doesnt-write-to-file]

\[END\]

[https_logging.apache.org_log4j_2.x_manual_migration.html]: https://logging.apache.org/log4j/2.x/manual/migration.html
[https_codedump.io_share_UwYEUh9AtRfg_1_log4j2-output-not-written-to-log-file]: https://codedump.io/share/UwYEUh9AtRfg/1/log4j2-output-not-written-to-log-file
[https_stackoverflow.com_questions_25118993_log4j-2-doesnt-write-to-file]: https://stackoverflow.com/questions/25118993/log4j-2-doesnt-write-to-file