Java Language Tutorial => How to use Log4j in Java code

Example

First need to create a final static logger object:

final static Logger logger = Logger.getLogger(classname.class);

Then, call logging methods:

//logs an error message
logger.info("Information about some param: " + parameter); // Note that this line could throw a NullPointerException!

//in order to improve performance, it is advised to use the `isXXXEnabled()` Methods
if( logger.isInfoEnabled() ){
    logger.info("Information about some param: " + parameter);
}

// In log4j2 parameter substitution is preferable due to readability and performance
// The parameter substitution only takes place if info level is active which obsoletes the use of isXXXEnabled().
logger.info("Information about some param: {}" , parameter);

//logs an exception
logger.error("Information about some error: ", exception);

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Java Language log4j / log4j2 How to use Log4j in Java code

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