how to write to a text file using to log4j?

Question

I'm wondering how to convert the following code to output those lines into a text file, and not to standard output:

import org.apache.log4j.Logger; import org.apache.log4j.PropertyConfigurator;

public class HelloWorld {

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

    public static void main(String[] args) {
        PropertyConfigurator.configure("log4j.properties");
        logger.debug("Sample debug message");
        logger.info("Sample info message");
        logger.warn("Sample warn message");
        logger.error("Sample error message");
        logger.fatal("Sample fatal message");
    }
}

The properties file is :

log4j.rootLogger=DEBUG, CA
log4j.appender.CA=org.apache.log4j.ConsoleAppender
log4j.appender.CA.layout=org.apache.log4j.PatternLayout
log4j.appender.FA.layout.ConversionPattern=%m%n

Thanks.

Solution 1

Change the ConsoleAppender to a FileAppender.

I find the org.apache.log4j.RollingFileAppender to be useful. If you use this, you must add a property for the fileName and may want to set the maxFileSize as well. Here is an example (put these in the log4j.properties file):

log4j.appender.NotConsole=org.apache.log4j.RollingFileAppender
log4j.appender.NotConsole.fileName=/some/path/to/a/fileName.log
log4j.appender.NotConsole.maxFileSize=20MB

There are other appenders. DailyRollingFileAppender rolls based on time. FileAppender does not roll. If you use the RollingFileAppender, you will need to guess as to a good value for maxFileSize and then address the size at a future date if it is causing issues.

Solution 2

Shortly use FileAppender instead of ConsoleAppender.

Here is a simple example of configuration. It additionally configures the layout. You can omit it for the first approach.

log4j.appender.F=org.apache.log4j.FileAppender
log4j.appender.F.File=mylog.log
log4j.appender.F.layout=org.apache.log4j.PatternLayout
log4j.appender.F.layout.ConversionPattern=%d{MM-dd@HH:mm:ss} %-5p (%13F:%L) %3x - %m%n

Solution 3

The following would be helpful:

Class containing main method

    package abc;

    import org.apache.log4j.Logger;
    import org.apache.log4j.PropertyConfigurator;

    public class ClassOne {
        static Logger logger = Logger.getLogger(ClassOne.class);

        public static void main(String[] args) {
             PropertyConfigurator.configure("log4j.info"); //log4j.info file should be in the class path(same location as ClassOne.class)

             logger.info("Program started.... "); //Whenever you want to write something to the log text file use logger.info("Log Message")

        }
    }

log4j.info file

   log4j.rootLogger=INFO, FILE

   # Define the file appender
   log4j.appender.FILE=org.apache.log4j.FileAppender // Replacing ConsoleAppender with FileAppender gives text file logging

   # Set the name of the file
   log4j.appender.FILE.File=src/abc/log.out //Here you can specify either absolute or relative path

   # Set the immediate flush to true (default)
   log4j.appender.FILE.ImmediateFlush=true

   # Set the threshold to debug mode
   log4j.appender.FILE.Threshold=debug

   # Set the append to false, overwrite
   log4j.appender.FILE.Append=false

   # Define the layout for file appender
   log4j.appender.FILE.layout=org.apache.log4j.PatternLayout
   log4j.appender.FILE.layout.conversionPattern=%d %m%n

Solution 4

following configuration should aslo work

direct log messages to stdout ###

log4j.appender.stdout=org.apache.log4j.FileAppender
log4j.appender.stdout.fileName=error.log
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

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