Why use SLF4J over Log4J for logging in Java

The main motivation of using SLF4J in your code to write log statements is, to make your program, independent of any particular logging library, which might require different configuration than you already have, and introduce more maintenance headache.

There is one more feature of SLF4J API, which convinced me to use SL4J over my long time favorite Log4j, that is know as place holder and represented as {} in code.

logger.debug("Processing trade with id: {} and symbol : {} ", id, symbol);

In SLF4J, we don't need String concatenation and don't incur cost of temporary not need String.

Here is the code of SLF4J logger method from it's Log4j Adapter class Log4jLoggerAdapter from slf4j-log4j12-1.6.1.jar.

public void debug(String format, Object arg1, Object arg2) {
    if (logger.isDebugEnabled()) {
      FormattingTuple ft = MessageFormatter.format(format, arg1, arg2);
      logger.log(FQCN, Level.DEBUG, ft.getMessage(), ft.getThrowable());
    }
}

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