How to use log4j without log4j.properties file

Usually when using log4j for logging log4j.properties file is used to configure log4j properties. But sometimes you may need to change these properties by your code. This tutorial simply show you how to set log4j properties through java code.
Download log4j-1.2.17.jar from Apache website and add it to your project.
Create a new java class and name it as LoggerTest. Create another java class and name it as LoggerUtil. Add following method to your LoggerUtil class so you don't need to have a log4j.properties file.

public static void initLogger() {
    try {
      String filePath = "D:/mylog.log";
      PatternLayout layout = new PatternLayout("%-5p %d %m%n");
      RollingFileAppender appender = new RollingFileAppender(layout, filePath);
      appender.setName("myFirstLog");
      appender.setMaxFileSize("1MB");
      appender.activateOptions();
      Logger.getRootLogger().addAppender(appender);
    } catch (IOException e) {
      e.printStackTrace();
    }
}

Explaining the method:
✪  First we define the log file path.
✪  Then we create a PatternLayout object by passing the pattern of the log entry.
✪  Note that here are using a RollingFileAppender. RollingFileAppender automatically rename the log files
    when they reach a certain size and create a new log file. By default it create a new log file when
    the current log file come to the size of 10MB. You can change this size by using one of
    appender.setMaximumFileSize() or appender.setMaxFileSize() methods.
✪  activateOptions() is an internal method and which throws an exception or give you warnings if it
    couldn't execute this methods correctly, for an example if file name is not set.
✪  Finally we append the appender to Root Logger.

Note that within the application running time you need to call this method only once.

We have almost finished our work. Now add a main method to your LoggerTest class as below and run it.

  public static void main(String[] args) {
    //calling initLogger() method to initialize properties. 
    //You need to call this method only once.
    LoggerUtil.initLogger(); 
    
    //Getting the already registered logger 'myFirstLog'
    Logger accessLog = Logger.getLogger("myFirstLog");
 
    accessLog.info("This is my first info message.");
    accessLog.warn("This is my first warn message.");
    accessLog.error("This is my first error message.");
    accessLog.fatal("This is my first fatal message.");
  }

Now open the log file(D:/mylog.log) and you will see the output.