I’m trying to learn more about the Spring Framework (without using SpringBoot) and currently i already have a basic RestController setup with embedded Tomcat server (version 10).

Everything works fine but i would like to customize the Catalina’s Log object so i could do stuff like JSON serializing of console logs.

I’m coming from a Nest.JS background and there it is very easy. Just register a new Logger with Nest and that’s it. I was hoping i could do something similar.

Apparently, Catalina uses a kind of wrapper around java.util.logging with it’s LogFactory. When creating the singleton for this class, it verifies if there is any service that implements the Log interface and uses that. If not, then it uses a default implementation (which is what im trying to override)

private LogFactory() {
        FileSystems.getDefault();

        // Look via a ServiceLoader for a Log implementation that has a
        // constructor taking the String name.
        ServiceLoader<Log> logLoader = ServiceLoader.load(Log.class);
        Constructor<? extends Log> m=null;
        for (Log log: logLoader) {
            Class<? extends Log> c=log.getClass();
            try {
                m=c.getConstructor(String.class);
                break;
            }
            catch (NoSuchMethodException | SecurityException e) {
                throw new Error(e);
            }
        }
        discoveredLogConstructor=m;
    }

I have implemented this Log interface (it is only a test class), but i cannot find out how i would make this ServiceLoader use it.

class CatalinaLogger implements Log {
  private Logger logger;
  private String name;

  public CatalinaLogger(String name) {
    this.name = name;

    this.logger = Logger.getLogger(name);
  }

  @Override
  public boolean isDebugEnabled() {
    return true;
  }

  @Override
  public boolean isErrorEnabled() {
    return true;
  }

  @Override
  public boolean isFatalEnabled() {
    return true;
  }

  @Override
  public boolean isInfoEnabled() {
    return true;
  }

  @Override
  public boolean isTraceEnabled() {
    return true;
  }

  @Override
  public boolean isWarnEnabled() {
    return true;
  }

  @Override
  public void trace(Object message) {
    logger.log(Level.FINER, String.valueOf(message));
  }

  @Override
  public void trace(Object message, Throwable t) {
    logger.log(Level.FINER, String.valueOf(message));
  }

  @Override
  public void debug(Object message) {
    logger.log(Level.FINE, String.valueOf(message));
  }

  @Override
  public void debug(Object message, Throwable t) {
    logger.log(Level.FINE, String.valueOf(message));
  }

  @Override
  public void info(Object message) {
    logger.log(Level.INFO, String.valueOf(message));
  }

  @Override
  public void info(Object message, Throwable t) {
    logger.log(Level.INFO, String.valueOf(message));
  }

  @Override
  public void warn(Object message) {
    logger.log(Level.WARNING, String.valueOf(message));
  }

  @Override
  public void warn(Object message, Throwable t) {
    logger.log(Level.WARNING, String.valueOf(message));
  }

  @Override
  public void error(Object message) {
    logger.log(Level.SEVERE, String.valueOf(message));
  }

  @Override
  public void error(Object message, Throwable t) {
    logger.log(Level.SEVERE, String.valueOf(message));
  }

  @Override
  public void fatal(Object message) {
    logger.log(Level.SEVERE, String.valueOf(message));
  }

  @Override
  public void fatal(Object message, Throwable t) {
    logger.log(Level.SEVERE, String.valueOf(message));
  }
  
}

Is my understanding of this problem correct? Either way, how could i solve this problem?