We connect logging to our JavaRush project (slf4f and log4j)

You can read how to connect Maven to your JavaRush project in this article of mine . The following assumes that you know how to do this. If we want to use slf4j, then we need a dependency:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.30</version>
</dependency>

After this we do:

public static void main(String[] args) throws IOException {
    Logger logger = LoggerFactory.getLogger(Solution.class);
    logger.info("hello world!");
}

And we get the error:

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.

Which is generally logical. slf4j is a wrapper, but what did we wrap it around? Nothing? Well, we got an error. You can wrap it around one of the following: log4j, util.logging, NOP, System.err, JCL, logback. More details in the original instructions . Let's look at the example of log4j and System.err: 1) Let's start with something simple, with System.err . To do this, add this one (slf4j-simple) to the previous dependency (slf4j-api).

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>1.7.30</version>
</dependency>

We take the same versions, as of May 10, 2021 it is 1.7.30. If you take dependencies from https://mvnrepository.com/ , do not forget to remove

<scope>test</scope>

Otherwise, your logs will only work in tests. 2) Now let's try to configure log4j , for this we need to add 2 dependencies: log4j itself and a layer between slf4j and log4j (slf4j-log4j12). It looks like this:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.30</version>
</dependency>
<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

It’s clear that we need to remove (slf4j-simple) so that slf4j doesn’t get confused about which logger it should work with. And leave (slf4j-api), since this is slf4j. Regarding the 2 added dependencies. log4j we are adding the old one (from May 2012, I don’t know why, you can experiment with others). Its version is 1.2.17. In order for slf4j to work with it, you need an appropriate layer - slf4j-log4j12, where the last characters (12) mean the log4j version. In this case, the version of slf4j-api and slf4j-log4j12 should be 1.7.30 - the latest stable one at the moment. After you have connected the dependencies and updated the Maven project. For log4j to work, you need 2 more things: 1) Set up a configuration file. We read, select, copy. 2) Read the log4j configuration before work:

PropertyConfigurator.configure("d:\\Java\\JavaRushTasks\\4.JavaCollections\\log4j.properties");

Well, or where you have the file. If you want to see all the logs, do not forget to set the logging level to ALL. We add to the resume - log4j & slf4j. You are gorgeous! If it helped - like, subscribe, bell!)))