Slf4j 日志文件保存在哪里？

我有以下进口产品:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

以及以下实例:

private static Logger logger = LoggerFactory.getLogger(Test.class);

以下是我的主要方法:

logger.info("SOME MESSAGE: ");

然而，我无法在任何地方找到输出，我所看到的只是在我的控制台中有:

21:21:24.235 [main] INFO  some_folder.Test - SOME MESSAGE:

如何定位日志文件？

请注意，我的构建路径中有以下内容:

slf4j-api-1.7.5.jar

slf4j-log4j12-1.6.4.jar

我读过类似问题的答案，但没有人真正说过如何解决这个问题。

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小开

It does not write to a file by default. You would need to configure something like the RollingFileAppender and have the root logger write to it (possibly in addition to the default ConsoleAppender).

小开

slf4j is only an API. You should have a concrete implementation (for example log4j). This concrete implementation has a config file which tells you where to store the logs.

enter image description here

When slf4j catches a log messages with a logger, it is given to an appender which decides what to do with the message. By default, the ConsoleAppender displays the message in the console.

The default configuration file is :

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">


<Appenders>
<!-- By default => console -->
<Console name="Console" target="SYSTEM_OUT">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</Console>
</Appenders>


<Loggers>
<Root level="error">
<AppenderRef ref="Console"/>
</Root>
</Loggers>
</Configuration>

If you put a configuration file available in the classpath, then your concrete implementation (in your case, log4j) will find and use it. See Log4J documentation.

Example of file appender :

<Appenders>
<File name="File" fileName="${filename}">
<PatternLayout>
<pattern>%d %p %C{1.} [%t] %m%n</pattern>
</PatternLayout>
</File>


...
</Appenders>

Complete example with a file appender : 

<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">


<Appenders>
<File name="File" fileName="${filename}">
<PatternLayout>
<pattern>%d %p %C{1.} [%t] %m%n</pattern>
</PatternLayout>
</File>
</Appenders>


<Loggers>
<Root level="error">
<AppenderRef ref="File"/>
</Root>
</Loggers>


</Configuration>
小开

As already mentioned its just a facade and it helps to switch between different logger implementation easily. For example if you want to use log4j implementation.

A sample code would looks like below.

If you use maven get the dependencies 

    <dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.6</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.5</version>
</dependency>

Have the below in log4j.properties in location src/main/resources/log4j.properties

            log4j.rootLogger=DEBUG, STDOUT, file


log4j.appender.STDOUT=org.apache.log4j.ConsoleAppender
log4j.appender.STDOUT.layout=org.apache.log4j.PatternLayout
log4j.appender.STDOUT.layout.ConversionPattern=%5p [%t] (%F:%L) - %m%n


log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=mylogs.log
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{dd-MM-yyyy HH:mm:ss} %-5p %c{1}:%L - %m%n

Hello world code below would prints in console and to a log file as per above configuration.

            import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class HelloWorld {
public static void main(String[] args) {
Logger logger = LoggerFactory.getLogger(HelloWorld.class);
logger.info("Hello World");
}
}

enter image description here

小开

The log file is not visible because the slf4j configuration file location needs to passed to the java run command using the following arguments .(e.g.)

-Dlogging.config={file_location}\log4j2.xml

or this:

-Dlog4j.configurationFile={file_location}\log4j2.xml

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