Log to different files based on logger name

Question

I have the following problem. I´m developing an application that uses a file appender for all loggers (log4j version 1.2). Everything works ok, but now i need to log to different files based on some runtime parameters.

As a restriction, i need also to restrict the amount of log4j.xml configuration info, because i don´t know beforehand how many values will this parameters take, and for that reason i can´t configure different appenders (FileAppenders) that point to different files in the log4j configuration file. I also need to restrict the amount of new code added, for example, it may be ok to pass the runtime parameter as part of the logger name (LoggerFactory.getLogger(runtimeParameter + getClass), etc) but i wouldn´t like to create a new FileAppender by code and then adding that new Appender to the recently created logger (as a side question, will this alternative work?).

I think that perhaps creating a new appender that open different files based on his provided name (based on the runtime parameter) will work, but i don´t know how to do that, and i don´t know how it will behave when executed concurrently (as it will be a single appender for all loggers).

Thank you and excuse my english!

Answer 1

It sounds like the easiest workaround in your case would be to programmatically configure and create logger objects in real time.

Yes it works. Lucky for you I just tackled this problem and have example code. This is for log4j2, though. I believe it's much easier and straightforward in 1.2

/**
 * Dynamically creates an instance of a Logger.
 * 
 * @param appenderName
 *            most often will be the name of the class this logger will
 *            belong to.
 * @param logFileName
 *            the file name to save the logs to
 * @return
 */
public static org.apache.logging.log4j.Logger createInstanceLogger(String appenderName,
        String logFileName) {
    //call getLogger() which will create and load a logger with a default configuration
    org.apache.logging.log4j.Logger logger = org.apache.logging.log4j.LogManager
            .getLogger(String.format("DynamicLogger%s",
                    String.valueOf(DynamicLogManager.loggerCount++)));
    org.apache.logging.log4j.core.Logger coreLogger = (org.apache.logging.log4j.core.Logger) logger; // cast logger to core logger to access protected methods
    org.apache.logging.log4j.core.LoggerContext context = coreLogger.getContext();
    org.apache.logging.log4j.core.config.BaseConfiguration configuration = (org.apache.logging.log4j.core.config.BaseConfiguration) context
            .getConfiguration();

    TriggeringPolicy compositePolicy = CompositeTriggeringPolicy.createPolicy(
            SizeBasedTriggeringPolicy.createPolicy("5mb"),
            TimeBasedTriggeringPolicy.createPolicy("1", "true"));

    String fileName = String.format("%1$s/%2$s", appenderName, logFileName);
    String filePattern = String.format("%1$s/%2$s.%%d{yyyy-MM-dd}",
            appenderName, logFileName);

    Layout<String> layout = PatternLayout.createLayout(DynamicLogManager._conversionPattern,
            configuration, RegexReplacement.createRegexReplacement("a^", "."), //empty regex replacement
            "utf-8", "false");

    Filter f = ThresholdFilter.createFilter("trace", "accept", "accept");

    Appender a = RollingFileAppender.createAppender(fileName, //fileName
            filePattern, //filePattern
            "true", //append
            appenderName, //appender name
            "true", //bufferred io
            "true", //immediate flush
            compositePolicy, //policy
            null, //strategy default
            layout, //layout
            f, //filter none
            "true", //ignore exceptions
            "false", //advertise
            "null", //advertise uri
            configuration //configuration
            );

    a.start();

    coreLogger.addAppender(a);

    //this is where we would figure out how to configure the logger to listen on a configuration file
    coreLogger.setLevel(Level.ALL); //set the log level of the logger that we are returning to Level.ALL

    return coreLogger; //cast logger back to Logger interface