log4j.properties example http://www.mkyong.com/logging/log4j-log4j-properties-examples/

log4j-console.properties

# 1. Output to Console
# All logging will be redirected to your console.
# Specific properties: PropertyConfigurator.configure("/log4j.properties");

# Root logger option
log4j.rootLogger=INFO, stdout
 
# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

log4j-file.properties

# 2. Output to File
# All logging will be redirected to your specified log file.
# Specific properties: PropertyConfigurator.configure("/log4j.properties");

# Root logger option
log4j.rootLogger=INFO, file
 
# Direct log messages to a log file
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=C:\\loging.log
log4j.appender.file.MaxFileSize=1MB
log4j.appender.file.MaxBackupIndex=1
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

log4j.properties

# 3. Output to Console and File
# All logging will be redirected to both log file and console.
# Specific properties: PropertyConfigurator.configure("/log4j.properties");

# Root logger option
log4j.rootLogger=INFO, file, stdout
 
# Direct log messages to a log file
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=C:\\loging.log
log4j.appender.file.MaxFileSize=1MB
log4j.appender.file.MaxBackupIndex=1
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n
 
# Direct log messages to stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

log4j.full.properties

#=================================================
# VNPT-Technology
# [Log4j configuration - Messaging module]
#=================================================

#log4j.rootLogger=debug,stdout,full,error,errorFilter 
log4j.rootLogger=debug,stdout, full, error


#stdout appender
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{dd/MM/yyyy HH:mm:ss} %5p [%t] %c{1}: %m%n
log4j.appender.stdout.Threshold=INFO


# full appender
log4j.appender.full=org.apache.log4j.DailyRollingFileAppender
log4j.appender.full.File=../log/full.log
log4j.appender.full.DatePattern='.'yyyy-MM-dd
log4j.appender.full.layout=org.apache.log4j.PatternLayout
log4j.appender.full.layout.ConversionPattern=%d{dd/MM/yyyy HH:mm:ss} %5p [%t] %c{1}: %m%n
log4j.appender.full.Threshold=INFO

# error appender
log4j.appender.error=org.apache.log4j.DailyRollingFileAppender
log4j.appender.error.File=../log/error.log
log4j.appender.error.DatePattern='.'yyyy-MM-dd
log4j.appender.error.layout=org.apache.log4j.PatternLayout
log4j.appender.error.layout.ConversionPattern=%d{dd/MM/yyyy HH:mm:ss} %5p [%t] %c{1}: %m%n
log4j.appender.error.Threshold=ERROR

Log4jConfig.java

// Check log4j is configured
if (!Logger.getRootLogger().getAllAppenders().hasMoreElements()) {
    try {
        InputStream is = ClassLoader.class.getResourceAsStream("/com/vntech/common/log4j.conf");
        if (is != null) {
            Properties props = new Properties();
            props.load(is);
            PropertyConfigurator.configure(props);
        } else {
            System.out.println("InputStream(/com/vntech/common/log4j.conf) is null");
        }
    } catch (IOException ex) {
        System.out.println("Cannot config log4j: " + ex.getMessage());
        System.out.println(ex);
    }

}

Multiple log files with log4j.properties

# 1. Predefine: og4j.logger.com.vaannila.admin=WARN,AdminFileAppender this property says that if you log to com.vaannila.admin or com.vaannila.admin.xxx.yyy.zzz then use AdminFileAppender (which is FileAppender with file 'admin.log')
# 2. Usage: After that: You can log to admin.log Logger.getLogger("com.vaannila.admin").log("To admin log") and to report log Logger.getLogger("com.vaannila.report").log("To report log")
# Specific properties: PropertyConfigurator.configure("/log4j.properties");

log4j.rootLogger=DEBUG

# AdminFileAppender - used to log messages in the admin.log file.
log4j.appender.AdminFileAppender=org.apache.log4j.FileAppender

log4j.appender.AdminFileAppender.File=admin.log

log4j.appender.AdminFileAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.AdminFileAppender.layout.ConversionPattern= %-4r [%t] %-5p %c %x - %m%n

# ReportFileAppender - used to log messages in the report.log file.
log4j.appender.ReportFileAppender=org.apache.log4j.FileAppender

log4j.appender.ReportFileAppender.File=report.log

log4j.appender.ReportFileAppender.layout=org.apache.log4j.PatternLayout
log4j.appender.ReportFileAppender.layout.ConversionPattern= %-4r [%t] %-5p %c %x - %m%n

log4j.logger.com.vaannila.admin=WARN,AdminFileAppender 
log4j.logger.com.vaannila.report=DEBUG,ReportFileAppender