Issue creating file for logs with SLF4J and Logback

I want to create an error log file in a specific folder. The folder has the following structure:

app 
|_ application.jar
|_ configuration.json
|_ logs
|_ log-error.log

I build the package and when I run the application with command line :
java -jar readExternalFilesFromJar-jar-with-dependencies.jar

I do obtain the following result:

[main] INFO fr.mydomain.app.ReadJson - Main Application called
[main] INFO fr.mydomain.app.JsonReader - getJson() method called
[main] ERROR fr.mydomain.app.ReadJson - Error message

I do not have issue making a log on console. My issue is that the log file is not created.

I added SLF4J and Logback dependencies in my pom.xml:

<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.30</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.30</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.2.3</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.2.3</version>
</dependency>

I also tried to configure Logback with a logback.xml file in my resource folder:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<timestamp key="times" datePattern="yyyyMMdd.HHmmss" />
<appender name="STDOUT" class="ch.qos.logback.core.FileAppender">
<file>${path}/${log.name}-${times}.log</file>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<appender name="FILE" class="ch.qos.logback.core.FileAppender">
<file>${path}/${log.name}-${times}.log</file>
<encoder>
<pattern>%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n</pattern>
</encoder>
</appender>
<logger name="fr.mydomain.app" level="debug" additivity="false">
<appender-ref ref="FILE" />
</logger>
<logger name="fr.mydomain.app" level="error" additivity="false">
<appender-ref ref="STDOUT" />
</logger>
<root level="error">
<appender-ref ref="FILE" />
</root>
</configuration>

In my main class I want to be able to configure the log file path and name. Why configuring those values in a java method ? the reason is rather simple. I want to be able to read those values from a configuration file.

I read some documentation on how to set file name and path :
https://mkyong.com/logging/logback-set-log-file-name-programmatically/

For this I added the following code :

public class ReadJson {
private static Logger logger = LoggerFactory.getLogger(ReadJson.class);
public static void main( String[] args ) throws Exception {
System.setProperty("path", "./logs");
System.setProperty("log.name", "error");
logger.info("Main Application called");
// déclaration de variables
System.setProperty("path", ".");
System.setProperty("log.name", "error");
...
}
}

I created a LogConfigurer class with a getLogger method:

public Logger getLogger(Configuration configuration, String docType) {
...
String logFileName = "whateverILog";
fileAppender = new FileAppender();
fileAppender.setContext(loggerContext);
fileAppender.setName("timestamp");
Logger root = (Logger) LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME);
root.setLevel(Level.ERROR);
fileAppender.setFile(logFolder + "\\"+ logFilename +".log");
encoder.setContext(loggerContext);
encoder.setPattern("%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n");
encoder.start();
fileAppender.setEncoder(encoder);
fileAppender.start();
logger = loggerContext.getLogger(getClass().getSimpleName());
logger.addAppender(fileAppender);
// OPTIONAL: print logback internal status messages
StatusPrinter.print(loggerContext);
// log something
logger.debug("Logger Implemented");
return logger;
}

In the main method I call :

LogConfigurer logConfigurer = new LogConfigurer();
Logger logger = logConfigurer.getLogger(configuration, docType);